U.S. patent application number 16/274924 was filed with the patent office on 2020-08-13 for method for dynamic control of light emission from phosphors with heat excitations.
The applicant listed for this patent is UCHICAGO ARGONNE, LLC. Invention is credited to Benjamin Diroll, Peijun Guo, Richard D, Schaller.
Application Number | 20200256519 16/274924 |
Document ID | / |
Family ID | 71945093 |
Filed Date | 2020-08-13 |
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United States Patent
Application |
20200256519 |
Kind Code |
A1 |
Diroll; Benjamin ; et
al. |
August 13, 2020 |
METHOD FOR DYNAMIC CONTROL OF LIGHT EMISSION FROM PHOSPHORS WITH
HEAT EXCITATIONS
Abstract
An optically emissive material and, in particular, materials for
use in single photon generation technologies, have multiple excited
energy states that have different decay rates and can emit photons
with different properties. A primary excitation radiation source is
configured to apply primary radiation to an optically emissive
material to excite the optically emissive material into a primary
excited state. A secondary excitation radiation source is
configured to apply secondary radiation to a thermal contribution
material to generate thermal energy in the thermal contribution
material. The thermal contribution material is physically
configured to transfer thermal energy to the optically emissive
material and excite the optically emissive material from the
primary excited state to a secondary excited state for dynamic
control of the emission rate, or emitted photon properties, of the
optically emissive material.
Inventors: |
Diroll; Benjamin; (Chicago,
IL) ; Guo; Peijun; (Woodridge, IL) ; Schaller;
Richard D,; (Clarendon Hills, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UCHICAGO ARGONNE, LLC |
Chicago |
IL |
US |
|
|
Family ID: |
71945093 |
Appl. No.: |
16/274924 |
Filed: |
February 13, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/502 20130101;
F21K 2/04 20130101; C09K 11/0811 20130101; F21V 9/32 20180201; B82Y
30/00 20130101; C09K 11/883 20130101; C09K 11/0827 20130101; B82Y
20/00 20130101 |
International
Class: |
F21K 2/04 20060101
F21K002/04; F21V 9/30 20060101 F21V009/30; C09K 11/07 20060101
C09K011/07 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made with government support under
Contract No. DE-AC02-06CH11357 awarded by the United States
Department of Energy to UChicago Argonne, LLC, operator of Argonne
National Laboratory. The government has certain rights in the
invention.
Claims
1. A method for controlling optical emissions of a material, the
method comprising: selecting a radiation emitting material, the
radiation emitting material having a primary excitation state and a
secondary excitation state, wherein the primary and secondary
excitation states have different decay rates; applying a primary
radiation to the radiation emitting material to excite the
radiation emitting material to the primary excitation state; and
applying a secondary radiation to a thermal contribution material
physically coupled to the radiation emitting material causing the
generation of thermal energy in the thermal contribution material,
and the thermal contribution material being physically configured
for thermal energy to flow from the thermal contribution material
to the radiation emitting material to promote the excited radiation
emitting material to the secondary excitation state.
2. The method of claim 1, wherein the primary excitation state of
the selected radiation emitting material is a dark excitation
state, and wherein the secondary excitation state of the selected
radiation emitting material is a bright excitation state.
3. The method of claim 1, wherein the primary excitation state of
the selected radiation emitting material is a bright excitation
state, and wherein the secondary excitation state of the selected
radiation emitting material is a dark excitation state.
4. The method of claim 1, wherein the primary excitation state of
the selected radiation emitting material is a slower transition
excitation state, and wherein the secondary excitation state of the
selected radiation emitting material is a faster transition
excitation state.
5. The method of claim 1, wherein the primary excitation state of
the selected radiation emitting material is a faster transition
excitation state, and wherein the secondary excitation state is a
slower transition excitation state.
6. The method of claim 1, wherein the primary excitation state of
the selected radiation emitting material emits a photon with a
horizontal polarization, and wherein the secondary excitation state
of the selected radiation emitting material emits a photon with a
vertical polarization.
7. The method of claim 1, wherein the thermal contribution material
comprises a ligand.
8. The method of claim 1, wherein the thermal contribution material
comprises an organic material.
9. The method of claim 1, wherein the thermal contribution material
comprises the same material as the radiation emitting material.
10. The method of claim 1, wherein the thermal contribution
material comprises a plurality of hydrocarbon surface ligands.
11. An optical device comprising: a radiation emitting material
having a primary excitation state and a secondary excitation state,
wherein the primary and secondary excitation states have different
decay rates; a thermal contribution material physically coupled to
the radiation emitting material and configured to provide thermal
energy to the radiation emitting material; a primary radiation
source configured to supply primary radiation to the radiation
emitting material to excite the radiation emitting material to the
primary excitation state; and a secondary radiation source
configured to provide secondary radiation to the thermal
contribution material to generate thermal energy in the thermal
contribution material.
12. The optical device of claim 11, wherein the primary radiation
source is configured to emit ultraviolet radiation.
13. The optical device of claim 11, wherein the primary radiation
source is configured to emit visible radiation.
14. The optical device of claim 11, wherein the secondary radiation
source is configured to emit infrared radiation.
15. The optical device of claim 11, wherein the radiation emitting
material comprises a phosphor.
16. The optical device of claim 11, wherein the radiation emitting
material comprises a III-V semiconductor material.
17. The optical device of claim 11, wherein the radiation emitting
material comprises a II-VI semiconductor material.
18. The optical device of claim 11, wherein the radiation emitting
material comprises a material with a spin-forbidden transition
state.
19. The optical device of claim 11, wherein the radiation emitting
material comprises a quantum dot.
20. The optical device of claim 11, wherein the radiation emitting
material comprises a bulk material.
Description
FIELD OF THE DISCLOSURE
[0002] The present disclosure relates to optically emissive
materials and, in particular, materials for use in single photon
generation technologies.
BACKGROUND
[0003] Light emission and the generation of photons is essential to
the operation of many current and prospective technologies, in
particular those which rely upon single-photon emission processes.
Single-photon sources are central for many fields including quantum
computing, quantum communications, quantum imaging and detection,
and quantum cryptography to name a few. There are currently many
forms of single-photon sources such as attenuated laser sources,
quantum dots, and entangled photon sources. One type of
single-photon source relies on radiative relaxation of an excited
phosphor to emit a single photon at a time.
[0004] Photon sources dependent on photon emission from a phosphor
are fundamentally limited by the rate at which the phosphor emits
photons. The duty cycle of a phosphor-based single-photon source
depends on the time it takes for a phosphor excitation to be
generated and for the relaxation of the phosphor excitation to the
ground state via photon emission. Generation of an excited
single-photon emitting phosphor depends on the mechanism of
excitation, but is typically rapid compared to the time-scale of
relaxation and, consequently, photon emission. For example, when
optical excitation of a phosphor is employed, excitation generation
is approximately instantaneous with a speed controlled by the pulse
time of the laser (e.g., tens of femtoseconds). Photon emission
from an excited phosphor depends on the electronic structure of the
phosphor, which is chiefly determined by the composition and
structure of the material. Most phosphors have many energetically
close excited electronic states that potentially emit photons with
distinct properties, such photon polarization.
[0005] Many single-photon sources that rely on de-excitation of a
phosphor have slow emission rates due to long relaxation times. For
example, a cadmium selenide quantum dot emission time can be as
much as 1 microsecond long under single-photon operating
conditions. Systems that rely on single-photon sources suffer from
slow photon emission rates which may result in low image
resolutions and low communication and/or data rate bandwidths among
other mal-effects.
SUMMARY OF THE DISCLOSURE
[0006] A method for controlling optical emissions of a material
including selecting a radiation emitting material, the radiation
emitting material having a primary excitation state and a secondary
excitation state, the primary and secondary excitation states
having different decay rates. The method further including applying
a primary radiation to the radiation emitting material to excite
the radiation emitting material to the primary excitation state,
and applying a secondary radiation to a thermal contribution
material physically coupled to the radiation emitting material
causing the thermal contribution material to generate thermal
energy, and the thermal contribution material being physically
configured for thermal energy to flow from the thermal contribution
material to the radiation emitting material to promote the excited
radiation emitting material to the secondary excitation state.
[0007] An optical device includes a radiation emitting material
having a primary excitation state and a secondary excitation state,
with the primary and secondary excitation states having different
decay rates. The optical device further includes a thermal
contribution material physically coupled to the radiation emitting
material and configured to provide thermal energy to the radiation
emitting material, a primary radiation source configured to supply
primary radiation to the radiation emitting material to excite the
radiation emitting material to the primary excitation state, and a
secondary radiation source configured to provide secondary
radiation to the thermal contribution material to generate thermal
energy in the thermal contribution material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1A is a diagram illustrating a phosphor at ground state
in a three-state quantum system.
[0009] FIG. 1B is a diagram illustrating radiation exciting a
phosphor from the ground state to a first excited state in a
three-state quantum system.
[0010] FIG. 1C is a diagram illustrating emission of radiation and
relaxation of a phosphor from a first excited state to the ground
state in a three-state quantum system.
[0011] FIG. 1D is a diagram illustrating heat energy (i.e. thermal
energy) exciting a phosphor from a first excited state into a
second excited state and the subsequent emission of radiation and
relaxation of a phosphor from the second excited state to the
ground state in a three-state quantum system.
[0012] FIG. 2A illustrates an embodiment of an optical emitter
having a phosphor, thermal contribution material, primary and
secondary radiations, and primary and secondary radiation
sources.
[0013] FIG. 2B illustrates an embodiment of an optical emitter
having cadmium selenide as a radiation emitting material, a
plurality of hydrocarbon surface ligands as a thermal contribution
material, primary and secondary radiations, and primary and
secondary radiation sources.
[0014] FIG. 2C illustrates an embodiment of an optical emitter
having lead halide perovskite as both a radiation emitting material
and a thermal contribution material, primary and secondary
radiations, and primary and secondary radiation sources.
[0015] FIGS. 3A-3D are a series of plots presenting emission data
from various sizes of cadmium selenide nanoparticles due to an
applied primary radiation.
[0016] FIGS. 3E-3H are a series of plots presenting emission data
from various sizes of cadmium selenide nanoparticles due to an
applied primary radiation and an applied secondary radiation.
[0017] FIGS. 4A and 4B are plots showing the photon emission over
time of a cadmium selenide nanoparticle due to an applied primary
radiation with associated decay time constants.
[0018] FIGS. 4C and 4D are plots showing the photon emission over
time of a cadmium selenide nanoparticle due to an applied primary
radiation and an applied secondary radiation with associated decay
time constants.
[0019] FIG. 5 is a plot showing photon emission over time from a
cadmium selenide nanoparticle with an applied primary radiation,
and various secondary radiations applied at various times
subsequent to the applied primary radiation.
[0020] FIG. 6 is a plot showing photon emission over time from a
lead halide perovskite crystal with an applied primary radiation,
and various secondary radiations applied at various times
subsequent to the applied primary radiation.
DETAILED DESCRIPTION
[0021] One class of single-photon sources relies on the
de-excitation of an excited phosphor for the emission of a single
photon. Typically, single-photon sources with emissive phosphors
are operated at low temperatures to achieve higher emission quantum
yields and narrow energy bandwidths of emissions. As used herein,
the phrase "low temperature," is used as would be understood by a
person of ordinary skill in the art and, specifically, refers to an
operational temperature for most single-photon emitting devices and
technologies, typically in the range of 1.5 to 5 K. At low
temperatures, the low ambient thermal energy of the environment
causes excitations to occupy the lowest possible excitation state
of the phosphor, which is typically a slow transition state, or a
dark state. A dark state or slow transition state can have a
relaxation time constant on the order of nanoseconds to
microseconds long. Typical single-photon emitters generally have
relaxation time constants on the scale of tens of nanoseconds. Dark
states involve a quantum mechanically forbidden transition so the
time-scale of radiative relaxation from a dark state to the ground
state is much longer than the transition time-scale for states that
do not have a forbidden transition. Transitions without a forbidden
transition that readily relax from the excited state to the ground
state and are known as fast transition states or bright states,
which can have relaxation time constants on the picosecond time
scale. For example, a cadmium selenide quantum dot can have slow
transition relaxation time constants, up to microseconds long,
while relaxation time constants for emissions from the cadmium
selenide bright states range from 10-100 picoseconds, up to five
orders of magnitude faster than the slow relaxation time
constants.
[0022] While the phrases dark state and slow transition state are
generally understood in the art as synonyms, and the phrases bright
state and fast transition state are likewise understood in the art
as synonyms, in order to avoid confusion we will generally use the
phrases dark state and bright state in this description when
referring to the categories of state transitions based on general
transition time scales. That is, dark states have relaxation time
constants on the order of nanoseconds to microseconds, while bright
states have relaxation time constants on the order of 10-100
picoseconds. In contrast, the phrases "slower transition state" and
"faster transition state" (as opposed to "slow transition state"
and "fast transition state") will be used in this description to
describe relative relaxation time constants, even if both of the
slow and fast transition states are bright or both of the slow and
fast transition states are dark. A slower transition state is any
state that has a longer relaxation time or slower transition than
another excited state referred to in the system. One example given
above pertains to a cadmium selenide quantum dot with a faster
transition state that has relaxation rates up to 100,000 times
faster than the relaxation rates of the slower transition state.
Other single photon emitters and materials may have faster
transition states that are only 2 to 5 times faster than a slower
transition state in the system. It should therefore be understood
that the faster transition states described herein can be any
excited state of a quantum system that exhibits a faster relaxation
time constant than the relaxation time constant of another excited
state referred to in that quantum system. The methods and devices
disclosed herein provide a means for controlling the rate of photon
emission and photon polarization through manipulation of an excited
phosphor into bright and dark states through thermal
excitations.
[0023] For embodiments herein, the terms "primary excitation
state", and "secondary excitation state" may also be used to
describe the energy states of a system. The term "primary
excitation state" should be understood to be a non-ground state of
a system, the transition to which is stimulated by a primary
radiation provided by a primary radiation source, as described
below. Similarly, the term "term "secondary excitation state"
should be understood to be a non-ground state of a system, the
transition to which is induced by thermal excitation caused,
directly or indirectly, by secondary radiation provided by a
secondary radiation source, as also described below.
[0024] In electromagnetics, it is common to distinguish between a
frequency, wavelength, energy, and color of electromagnetic
radiation. Each of these four characteristics is related to the
other three. For example, the wavelength, in nanometers (nm), and
frequency, in hertz (Hz), for a specified electromagnetic radiation
are inversely proportional to each other. Similarly, the energy, in
electron-volts (eV) or joules (J), of electromagnetic radiation is
proportional to the frequency of that radiation. Therefore, for a
given radiation at a given frequency, there is a corresponding
wavelength and energy.
[0025] The fourth of the aforementioned characteristics, color,
typically represents a group or band of frequencies or wavelengths.
For example, the color blue is commonly defined as electromagnetic
radiation with a wavelength from 450 nm to 495 nm. This wavelength
band also corresponds to frequencies from 606 THz to 668 THz, and
energies of 2.5 to 2.75 eV. The color blue, then, is any radiation
with one of those wavelengths, or radiation with multiple
wavelengths in that band. Therefore, the term color may refer to
one specific wavelength, or a band of wavelengths. Some areas of
trade in electromagnetics prefer the use of one of the four terms
over the others (e.g., color and wavelength are preferred when
discussing optical filters, whereas frequency and energy are
preferred when optical excitation processes). Therefore, the four
terms may be understood to be freely interchangeable in the
following discussion of electromagnetic radiation, phosphors, and
single-photon sources.
[0026] Additionally, as a person of ordinary skill in the art would
understand, the terms excited state, excitation state, quantum
state, and energy state can be interchangeable when describing the
state of a system. Also, the states of a system may also be
described as having or existing with a specific energy, E,
associated with the state. Therefore, it should be understood that
a state may be referred to as an energy state E, or a state with
energy E interchangeably. As such, it should be understood that a
label E may refer to the energy of a state and/or to the state
itself. In photonics, and specifically when considering single
photon emission, the terms emission time, relaxation time,
relaxation rate, transmission rate, transition time, decay rate,
and decay time are also understood to be interchangeable in most
cases. In addition, a person of ordinary skill in the art would
recognize that the terms excite, promote, or energize are often
interchangeable when discussing the transition of a system from one
energy level to another, higher, energy level, and similarly the
terms de-excite, rest, and recombine may be used interchangeably
when discussing the transition of a system from one energy level to
another, lower, energy level.
[0027] FIGS. 1A-1D are diagrams illustrating systems with three
potential energy states. FIGS. 1A-1D are typical representations of
energy bands for quantum dots, electrons, or any other particle or
ensemble able to occupy various energy bands. FIGS. 1A-1D show a
radiation emitting phosphor, Ph, and three energy states: a ground
energy state, E.sub.G, a primary excited energy state, and a
secondary excited energy state. In FIGS. 1A-1D, the primary excited
energy state is the lowest excited state or first excited energy
state with energy E.sub.1, and the secondary excited energy state
is a second excited energy state with an energy E.sub.2, greater
than E.sub.1. As illustrated in FIG. 1A, at temperatures on the
order of Kelvins, the phosphor typically exists in or occupies the
ground energy state. The phosphor remains in the ground energy
state until some form of excitation or perturbation changes the
state of the phosphor. FIG. 1B illustrates an excitation energy
provided by a photon with energy E.sub.p1. The photon provides
energy to the phosphor exciting it to the first excited state. Once
in the first excited state, the phosphor may de-excite or relax
back down into the ground state and emit a photon with energy
E.sub.p1 as illustrated in FIG. 10. Alternatively, as illustrated
in FIG. 1D, instead of relaxing back into the ground state from the
first excited energy state, a second further perturbation with
energy E.sub.12 may be provided to the phosphor to excite the
phosphor from the first excited energy state into the second
excited energy state. In the illustration of FIG. 1D, and the
embodiments herein, thermal energy or heat is provided to the
phosphor causing the transition from the first excited energy state
to the second excited energy state. Once in the second excited
energy state, the phosphor may relax back into the ground energy
state emitting a photon with energy E.sub.p2.
[0028] Quantum states of atoms and particles have quantized
energies determined by intrinsic properties such as the spin of a
particle, and extrinsic factors such as an applied electric field,
among other factors. Excited quantum states also have
characteristic decay or relaxation times. Typically, the relaxation
time of an atom, particle, molecule, or material in a given excited
quantum state exhibits an exponential rate of decay. The length of
the decay time of a given quantum state depends on the density of
states and the temperature of the material among other factors.
Some quantum states have forbidden transitions which are
transitions forbidden by quantum mechanics, typically due to the
required conservation of angular momentum. Such forbidden states
are known as slow transition states or dark states because the
relaxation time can be long compared to other faster non-forbidden
transition states. For example, the intrinsic relaxation time or
emission time-scale of cadmium selenide quantum dots can reach 1
microsecond, while faster non-forbidden cadmium selenide quantum
states have relaxation times or emission time-scales around 10 to
100 picoseconds at operational temperatures. The faster
non-forbidden transition states are also known as fast transition
states or bright states.
[0029] In some embodiments, the secondary excited state is a bright
state, which can be used to induce emissions of photons from a
material at faster rates than emissions from the dark state of the
single-photon emitter. Referring again to FIGS. 1A-1D, in an
embodiment of a method the primary excited state is the first
excited state of a phosphor or radiation emitting atom, particle,
molecule, or material, E.sub.1, which may be a dark transition
state, and the secondary excited state is the second excited state
of the atom, particle, molecule, or material, E.sub.2, which may be
a bright transition state. FIG. 1B. illustrates a photon or
radiation with an energy E.sub.p1 exciting the atom, particle,
molecule or material from the ground state with energy E.sub.g into
the first excited state which is a dark state. As illustrated in
FIG. 1D, once the atom, particle, molecule, or material is in the
first excited/dark state, thermal energy with energy E.sub.12 may
be provided to the atom, particle, molecule, or material to excite
the atom, particle, molecule, or material into the second
excited/bright state, instead of the atom, particle, molecule, or
material relaxing back to the ground state from the first excited
state as shown in FIG. 10. In embodiments that employ thermal
energy to excite an atom, particle, molecule, or material from a
first dark state to a second bright state, the emission time of the
atom, particle, molecule, or material may be controlled and, more
specifically, shortened compared to the intrinsic relaxation time
of the dark first excited state. The duty cycle or output rate of
single photon emission sources may be increased considerably
through a second excitation from a first dark state to a second
bright state. At sufficiently low operational temperatures, on the
order of 1 to 5 K, the thermal occupation of the excited state
manifold is typically exclusively in the lowest or first excited
energy state, which is often a dark state for direct bandgap
materials which are considered candidate phosphors for
single-photon emission.
[0030] In contrast to the embodiment of the previous paragraph, in
other embodiments, the secondary excited state may be a dark state
that may enable the ability to slow down or suppress photon
emissions from a single-photon emitter. In reference again to FIGS.
1A-1D, in an alternative embodiment of a method, the primary
excited state is the first excited state of a phosphor or radiation
emitting atom, particle, molecule, or material, E.sub.1, which may
be a bright state, and the secondary excited state is the second
excited state of an atom, particle, molecule, or material, E.sub.2,
may be a dark state. FIG. 1B illustrates the photon or radiation
with an energy E.sub.p1 exciting the atom, particle, molecule or
material from the ground state with energy E.sub.g into the first
excited state, which is a bright state. As illustrated in FIG. 1D,
once the atom, particle, molecule, or material is in the first
excited/bright state, thermal energy with energy E.sub.12 may be
provided to the atom, particle, molecule, or material to excite the
atom, particle, molecule, or material into the second dark excited
state, instead of the atom, particle, molecule, or material
relaxing back to the ground state from the first excited state as
shown in FIG. 1C. In embodiments that employ thermal energy to
excite an atom, particle, molecule, or material from a first bright
state to a second dark state, the emission time of the atom,
particle, molecule, or material may be controlled and, more
specifically, lengthened compared to the intrinsic relaxation time
of the bright first excited state.
[0031] In other embodiments the primary and secondary excitation
states may each be a dark state. The primary excitation state may
be a dark state with a faster transition time than the dark state
that is the secondary excitation state. Conversely, the primary
excitation state may be a dark state with a slower transition time
than the dark state that is the secondary excitation state.
Similarly, in other embodiments the primary excitation state and
secondary excitation state may each be a bright state. In
embodiments with the primary and secondary excitation states being
bright states, the primary excitation state may be a bright state
with a transition time that is either faster or slower than the
transition time of the bright state that is the secondary
excitation state.
[0032] Further in reference again to FIGS. 1A-1D, in yet another
alternative embodiment of a method, the primary excited state may
be the first excited state of a phosphor or radiation emitting
atom, particle, molecule, or material, E.sub.1, which may be an
excited state that emits a photon with a horizontal polarization
during relaxation, and the secondary excited state may be the
second excited state of an atom, particle, molecule, or material,
E.sub.2, which may be an excited state that emits a photon with a
vertical polarization during relaxation. FIG. 1B illustrates the
photon or radiation with an energy E.sub.p1 exciting the atom,
particle, molecule or material from the ground state with energy
E.sub.g into the first excited state, which emits a horizontally
polarized photon. FIG. 1C shows the de-excitation or relaxation of
the atom, particle, molecule, or material from the first excited
state to the ground state emitting a horizontally polarized photon
with energy E.sub.p1. Alternative, instead of allowing the atom,
particle, molecule, or material to relax from the first excited
state to the ground state, FIG. 1D illustrates a scenario where
thermal energy with energy E.sub.12 is provided to the atom,
particle, molecule, or material exciting the atom, particle,
molecule, or material from the first excited state into the second
excited state. The atom, particle, molecule, or material may
de-excite or relax from the second excited state to the ground
state emitting a vertically polarized photon with energy E.sub.p2.
Therefore, the polarization of an emitted photon or emitted
radiation may be controlled in embodiments with first and second
excited states that emit photons with different polarizations.
[0033] In the embodiments described, the phosphor or radiation
emitting atom, particle, molecule, or material is described as
having only three quantum states: a ground state, a primary excited
state, and a secondary excited state. In many embodiments described
herein the primary excited state is a first excited energy state
with energy E.sub.1, and the secondary excited state is a second
excited energy state with energy E.sub.2 that is greater than
E.sub.1. In other embodiments the atom, particle, molecule, or
material may have three, four, five, or more quantum states
including but not limited to orbital angular momentum states, spin
states, fine structure states, Zeeman split states, Stark shifted
states, Stark split states, degenerate states, or any other quantum
state or energy state. In embodiments with only two excited energy
states, it is to be understood that the term first excited state
refers the lower of the two excited energy states. In embodiments
with more than two excited states it should be understood that the
numerical labeling (i.e., first, second, third, etc.) denotes the
relative energy levels of the excited states from the first excited
state having a lowest excited energy level, to the second excited
state having the next lowest excited energy level, to the third
excited state having the third lowest excited energy level, and so
on sequentially for each subsequent energy level. In any
embodiment, the primary excited energy state may be any of the
excited energy states of the system, and the secondary excited
energy state may be any other of the excited energy states of the
system. In addition, in embodiments that enable the control of
emitted photon polarization, the photon polarizations may be
horizontal, vertical, diagonal, linear, right- or left-circular,
elliptical, or any other polarization.
[0034] The temperature of the phosphor or radiation emitting atom,
particle, molecule, or material could be controlled through
electronic means providing thermal energy or heat to the atom,
particle, molecule, or material. Typically, electronic temperature
control may cause multiple excitations enabling undesirable
multi-photon emissions. Multiple excitations may also lead to
non-radiative recombination, such as Auger recombination, and
typically dissipates heat resulting in a potentially undesirable
increase in the temperature of a material or system. Therefore, it
is desirable to provide thermal energy to the atom, particle,
molecule, or material without electronic excitation.
[0035] FIG. 2A illustrates an embodiment of an optical emitter 200
with a radiation emitting material 202 and a thermal contribution
material 212 that provides thermal energy to the radiation emitting
material 202 without electronic excitation. The optical emitter 200
of FIG. 2A may implement the methods illustrated by FIGS. 1A-1D and
described herein. Therefore, the following description of the
optical emitter 200 will refer to both FIG. 2A and FIGS. 1A-1D
simultaneously. In an embodiment, the radiation emitting material
202 of the optical emitter 200 in FIG. 2A may be a semiconductor
nanoparticle and the thermal contribution material 212 may be a
ligand bound to the semiconductor nanoparticle. A primary radiation
source 204 may provide primary radiation 206 to the nanoparticle to
excite the nanoparticle from a ground state, E.sub.g, to the
primary excited state that is a first excitation energy state,
E.sub.1, as illustrated in FIG. 1B. A secondary radiation source
208 may provide secondary radiation 210 to the thermal contribution
material 212 (e.g., the ligand) to cause the generation of thermal
energy in the material 212. To reach thermal equilibrium, the
induced thermal energy or heat in the material 212 may flow to the
radiation emitting material 202, promoting the radiation emitting
material 202 from the first excitation energy state, E.sub.1, into
the secondary excited state that is a second excitation energy
state, E.sub.2, as illustrated in FIG. 1D. The radiation emitting
material 202 may de-excite or relax from the second energy state,
E.sub.2, back to the ground state, E.sub.g, by emitting a photon
with energy E.sub.p2. The optical emitter 200 of FIG. 2A enables
dynamic control of photon emissions, and prevents electronically
induced multi-photon emission by utilizing an intermediary ligand
as the thermal contribution material 212 to the semiconductor
nanoparticle that is the radiation emitting material 202.
[0036] While the radiation emitting material 202 in the embodiment
of the optical emitter 200 of FIG. 2A is described as a
semiconductor nanoparticle, the radiation emitting material 202 may
alternatively be a quantum dot, a non-semiconductor nanoparticle, a
nanocrystal, a bulk material, a monolayer or 2D material, a
nanorod, a nanowire, any other nanostructure, or any other material
able to emit radiation. Additionally, the radiation emitting
material 202 of FIG. 2A may be cadmium selenide, a halide
perovskite, a rare earth material, a III-V semiconductor material,
a II-VI semiconductor material, an inorganic material, a molecular
singlet, a molecular triplet, or any other atom, molecule, or
assembly with a spin-forbidden or other forbidden transition
state.
[0037] The thermal contribution material 212 of FIG. 2A may be a
ligand. A ligand is not to be understood as an ion or molecule to
be attached or bound to a metal atom, but rather as a molecule that
binds to another metal or non-metal atom, particle, molecule, or
material. While the thermal contribution material 212 of FIG. 2A is
represented by generic bold lines, the thermal contribution
material 212 may be a coating on a molecule or nanoparticle, a
molecular antenna structure, or any other ligand or material able
to bond with, and provide thermal energy to, the radiation emitting
material 202.
[0038] The primary and secondary radiation sources 204 and 208 may
each be a laser, a light emitting diode, a single-photon source, a
black-body radiation source, a visible radiation source, an
infrared radiation source, or any other source or combination of
sources able to provide the desired radiation to the radiation
emitting material 202 and the thermal contribution material 212.
Accordingly, the primary and secondary radiations 206 and 210 may
each be ultraviolet radiation, visible radiation, infrared
radiation, microwave radiation, or any other radiation or
combination of radiations with wavelengths or frequencies able to
excite the radiation emitting material 202, and generate or induce
thermal energy in the thermal contribution material 212 as desired.
The primary and secondary radiations 206 and 210 may also each be
continuous radiation, pulsed radiation with a constant duty cycle,
pulsed radiation with a duty cycle that increases or decreases over
time, pulsed radiation with a pulse repetition frequency that
increases or decreases over time, pulse radiation with a radiation
frequency that increases or decreases over time, pulsed radiation
with an arbitrary pulse pattern, pulsed radiation with a
predetermined pulse pattern, pulsed radiation with a probabilistic
pulse pattern or sequence, or any other pulsed radiation
pattern.
[0039] FIG. 2B illustrates a particular embodiment of an optical
emitter 220 with a cadmium selenide nanocrystal 222 made of
multiple cadmium selenide molecules, as the radiation emitting
material 202. In the optical emitter 220, a plurality of
hydrocarbon surface ligands 232 acts as the thermal contribution
material 212. In this embodiment, a primary radiation source 224
may provide primary radiation 226 in the visible or ultraviolet
range to excite the cadmium selenide in the nanocrystal 222 into
the lowest, first excited energy state of cadmium selenide. The
bandgap of cadmium selenide is 1.74 eV, so radiation with an energy
of 1.74 eV or greater is required to excite the cadmium selenide in
the cadmium selenide nanocrystal 222 from the ground state into the
first excited state. In embodiments, it is desirable for the
primary radiation 226 to have an energy greater than the bandgap
energy of the radiation emitting material 202 to induce extra
thermal energy in the radiation emitting material allowing for
initial excitations into the higher energy, second excited state.
In cadmium selenide, the second excited state is a faster
transition state than the first excited, lower energy state.
Therefore, applying primary radiation 226 that is able to promote
at least some of the cadmium selenide in the nanocrystal 222 into
the second, faster transition energy state results in an initial
radiation emission followed later by the radiation emission from
any cadmium selenide excited into the first, slower transition
energy state. A second radiation source 228 may provide secondary
radiation 230 to the plurality of hydrocarbon surface ligands 232
coating the cadmium selenide nanocrystal 222. The secondary
radiation 230 may be in the mid-infrared range which has energies
insufficient for exciting cadmium selenide from the ground state
into the first excited state. It is also desirable for the
secondary radiation 230 to have frequencies that are resonant with
the vibrations of the plurality of hydrocarbon surface ligands 232.
The C--H bonds in the plurality of hydrocarbon surface ligands 232
have vibrational resonances in the 3400 to 3600 nm range.
Therefore, utilizing infrared radiation as the secondary radiation
230 does not create any new excitations, but may perturb already
existing excitations. The secondary radiation 230 may induce
thermal energy in the plurality of hydrocarbon surface ligands 232,
which is transferred or flows from the plurality of hydrocarbon
surface ligands 232 to the cadmium selenide nanocrystal 222. The
thermal energy may excite any excited cadmium selenide in the
cadmium selenide nanocrystal 222 from the first excitation state
into the second, faster transition excitation state resulting in
further radiation emission, and enabling dynamic control of
emission from the cadmium selenide nanocrystal 222. As one will
understand in view of this specification, the secondary radiation
210 may be applied to the thermal contribution material 212, of
FIG. 2A, at a time before applying the primary radiation 206 to the
radiation emitting material 202 due to the fact that it takes time
for the thermal energy to propagate from the thermal contribution
material 212 to the radiation emitting material 202. The timing of
applying the primary and secondary radiations 206 and 210 may be
determine by the thermal properties of the thermal contribution
material 212 and the radiation emitting material 202.
[0040] While a plurality of hydrocarbon surface ligands 232 in the
optical emitter 220 of FIG. 2B have a 15 carbon backbone, the
thermal contribution material may be any number of other types of
ligands. For example, the thermal contribution material 212 of FIG.
2A may be a C.sub.1-50alkylene. The backbone of the
C.sub.1-50alkylene may contain one or more heteroatoms selected
from O, NH, and/or S. The thermal contribution material 212 of FIG.
2A may also be any other ligand, structure, or material able to
generate thermal energy and transfer the generated heat or thermal
energy to the radiation emitting material 202.
[0041] FIG. 2C illustrates an embodiment of an optical emitter 240
that employs lead halide perovskite 242 as the radiation emitting
material 202. The lead halide perovskite 242 has an energy band
structure with the lowest, first excited energy state being a first
faster transition excited state, and a second excitation state,
with energy greater than the first faster excitation state, being a
slower transition excitation state. Therefore, the lead halide
perovskite 242 has the opposite relative excitation state decay
speeds of the embodiment implementing cadmium selenide as the
radiation emitting material 202. Due to the vibration resonances of
lead halide perovskite 242, the lead halide perovskite 242 may act
as both the radiation emitting material 202 and the thermal
contribution material 212 of the optical emitter 240, removing the
need for a second material, coating, or antenna to act as the
thermal contribution material 212. It is therefore possible to slow
the emission of photons from the lead halide perovskite 242 using a
primary and secondary radiation source 244 and 248. A primary
radiation source 244 may provide primary radiation 246 to the lead
halide perovskite 242 to excite at least some of the lead halide
perovskite 242 from the ground energy state to the first, fast
transition excited energy state. The second radiation source 248
may provide secondary radiation 250 to the lead halide perovskite
242 to generate thermal energy in the lead halide perovskite 242
and further excite any excited lead halide perovskite 242 from the
first excited energy state to the second, slower transition excited
energy state.
[0042] FIGS. 3A-3H are a series of plots presenting emission time
vs. emitted photon wavelength for cadmium selenide nanoparticles
(e.g., as shown in FIG. 2B) or nanocrystals of various sizes. The
top row, FIGS. 3A-3D present emission data after visible band, 400
nm, primary radiation is applied to the cadmium selenide
nanocrystals at time t=0. The cadmium selenide excited into the
second or faster transition excited energy state emits an initial
band of photons observed in FIGS. 1A-1D near the time that the
primary radiation is applied, at t=0, followed by an exponential
decay of subsequent slower emissions. The bottom row, FIGS. 3E-3H
present emission data from cadmium selenide with the application of
both a primary radiation with a wavelength of 400 nm, and a
secondary radiation with a wavelength of 3460 nm applied 500
picoseconds after the primary radiation. The application of the
secondary radiation promotes some of the cadmium selenide from the
first slower transition excitation energy level into the second
faster transition excitation energy level thereby inducing faster
radiation emission as evidenced by the second bright emission band
at t=500 ps in FIGS. 3E-3H. The various sizes of the cadmium
selenide nanocrystals in FIGS. 3A-3H determine how much cadmium
selenide is present and therefore how much primary radiation is
absorbed and how many photons are emitted by the cadmium selenide
nanocrystal. While the secondary radiation is applied at a time
t=500 ps after the primary radiation is applied, the secondary
radiation could be applied at 10, 24, 50, 100, 200, 300, 400, 600,
800, 1000 picoseconds after the primary radiation is applied, or
any time that any cadmium selenide is in the first slower
transition excited state.
[0043] FIGS. 4A and 4B are plots showing the integrated
time-resolved photon emission over time for various sizes of
cadmium selenide nanoparticles at a temperature of 5 Kelvin with a
primary radiation excitation of 400 nm. FIG. 4A shows the faster
transition time constants for the four sizes of cadmium selenide
nanoparticles with transition times on the order of tens of
nanoseconds. The faster transition time constants reported in FIG.
4A are determined by a biexponential fit to the presented data and
represent a statistical measure of how long a typical cadmium
selenide molecule exists in the second, faster transition
excitation state before relaxing into the ground state and emitting
a photon. FIG. 4B presents the same data as FIG. 4A over an
expanded time period. The slower transition time constants for four
different sized cadmium selenide nanoparticles are presented in
FIG. 4B with transition times on the order of nanoseconds. The
slower transition time constant values presented in FIG. 4B are
determined by a biexponential fit to the presented data and
represent a statistical measure of how long a typical cadmium
selenide molecule exists in the first, slower transition excitation
state before relaxing to the ground state and emitting a photon.
The data presented in FIGS. 4A and 4B show that the faster and
slower transition excitation state time constants of cadmium
selenide differ by over two orders of magnitude.
[0044] FIGS. 4C and 4D display plots showing the integrated
time-resolved photon emission over time for various sizes of
cadmium selenide nanoparticles at a temperature of 5 Kelvin with a
primary radiation excitation of 400 nm, followed by a secondary
radiation excitation with a wavelength of 3460 nm applied 500 ps
after the primary radiation excitation. The curves shown in FIG. 4C
have faster transition times determined by a biexponential fit that
are very close to the faster transition times reported in FIG. 4A,
with transition times on the order of tens of picoseconds. In FIG.
4C there is a feature at t=500 ps that is not present in the data
shown in FIG. 4A. An increase in photon emission is observed at
t=500 ps which is at the time that the secondary radiation is
applied to the cadmium selenide nanoparticles. FIG. 4D is a close
up or zoom in on the increased emission feature at t=500 ps which
exhibits a transition time or lifetime constant on the order of
tens of picoseconds, which is the same magnitude as the lifetime
constant of the second faster transition excitation state. The
faster transition feature exhibited in FIGS. 4C and 4D, that is not
present in FIGS. 4A and 4B, can be concluded to be the result of
thermal energy transferring into the cadmium selenide and promoting
cadmium selenide molecules from a first slower transition excited
state into a second faster transition excited state due to the fact
that the secondary radiation at 3460 nm does not provide sufficient
energy to excite cadmium selenide from the ground state into any
excited states.
[0045] FIG. 5 is a plot of emission data demonstrating the temporal
control, and potential temporal resolution of photon emission
control enabled by the embodiments herein. Emitted photon counts
are reported in arbitrary units (a.u.) and the time dimension is
reported in picoseconds. The lowest curve 502 on the plot of FIG. 5
shows photon emissions from a 3.8 nm cadmium selenide nanoparticle
with a primary radiation applied at time t=0 ps and no subsequent
applied radiation. The three other curves 504, 506, and 508,
present in FIG. 5 show the photon emissions from a 3.8 nm cadmium
selenide nanoparticle with a primary radiation applied at time t=0,
and subsequent secondary radiations applied at times t=300, 500,
and 700 ps. The three curves 504, 506, and 508 with both an applied
primary and secondary radiation exhibit two emission features
corresponding in time with the applied primary and secondary
radiations, while the curve 502 with no applied secondary radiation
only exhibits the initial first emission feature at time t=0. The
timing precision of the second emission features in the curves 504,
506, and 508 of FIG. 5 can be on the order of femtoseconds which is
determined by the timing and shaping of the secondary radiation
pulse. While the temporal control or resolution demonstrated by the
curves in FIG. 5 is on the scale of 100 ps the temporal control is
limited, in theory, by the decay time constant of the faster
excited state, which for cadmium selenide is on the order of tens
of picoseconds. Another property which may contribute to the timing
precision and resolution of the secondary emission from a material
is the time required for thermal energy to transfer from a thermal
contribution material to a phosphor, which varies for different
materials.
[0046] FIG. 6 presents a plot with a curve 602 showing photon
emission in arbitrary units over time from a single crystal of lead
halide perovskite (e.g., as shown in FIG. 2C) with a primary
radiation with a wavelength of 400 nm applied at time t=0 ps, with
no subsequent applied secondary radiation. The other five curves
604, 606, 608, 610, and 612 in the plot of FIG. 6 show photon
emission over time for a single crystal of lead halide perovskite
with a primary radiation excitation with a wavelength of 400 nm
applied at time t=0 ps, followed by a secondary radiation
excitation with a wavelength of 3200 nm applied to the halide
perovskite at various times subsequent to the applied primary
radiation. A vertical dotted line at time t=0 ps through all of the
curves shows the initial emission peak from the lead halide
perovskite due to the applied primary radiation exciting the lead
halide perovskite into the first faster transition state. A second
vertical dotted line is present on each of the top five curves 604,
606, 608, 610, and 612 showing the various times at which the
secondary radiation was applied. At the second vertical lines,
there exists a second emission feature on each of the curves 604,
606, 608, 610, and 612 with a brief rapid decrease in emission
resulting in an emission trough. The emission trough present in the
curves 604, 606, 608, 610, and 612 of FIG. 6 coincides temporally
with the application of the secondary radiation, suggesting that
the secondary radiation has excited some of the lead halide
perovskite from the first faster transition excited state into the
second slower transition excited state causing a brief period of
time where less emission occurs.
[0047] The embodiments of dynamically controllable optical emitters
presented herein may be implemented in photon sources to control
optical emissions with picosecond time-scale resolution. The
embodiments described herein also allow for the control of the
temperature of an optical emitting device without electronic
excitation, which helps reduce the amount of multi-photon emissions
and can reduce non-radiative recombinations such as Auger
recombinations. The secondary radiation or thermal excitation
radiation can be tuned in power, time, and/or energy to enhance
deterministic photon emissions of the optical emitter. In addition,
the methods and embodiments of optical emitters described herein
may be used to program probabilistic pulse sequences that are more
complex than the exponential decay that naturally occurs in many
single photon sources. Current single photon source technologies
can operate at 300 MHz, or one photon emission every 3 ns, which is
10 to 50 times slower than the demonstrated capabilities of the
methods and embodiments of optical emitters described herein.
[0048] The following list of aspects reflects a variety of the
embodiments explicitly contemplated by the present application.
Those of ordinary skill in the art will readily appreciate that the
aspects below are neither limiting of the embodiments disclosed
herein, nor exhaustive of all of the embodiments conceivable from
the disclosure above, but are instead meant to be exemplary in
nature.
[0049] 1. A method for controlling optical emissions of a material,
the method comprising: selecting a radiation emitting material, the
radiation emitting material having a primary excitation state and a
secondary excitation state, wherein the primary and secondary
excitation states have different decay rates; applying a primary
radiation to the radiation emitting material to excite the
radiation emitting material to the primary excitation state; and
applying a secondary radiation to a thermal contribution material
physically coupled to the radiation emitting material causing the
generation of thermal energy in the thermal contribution material,
and the thermal contribution material being physically configured
for thermal energy to flow from the thermal contribution material
to the radiation emitting material to promote the excited radiation
emitting material to the secondary excitation state.
[0050] 2. The method of aspect 1, wherein the primary excitation
state of the selected radiation emitting material is a dark
excitation state, and wherein the secondary excitation state of the
selected radiation emitting material is a bright excitation
state.
[0051] 3. The method of aspect 1, wherein the primary excitation
state of the selected radiation emitting material is a bright
excitation state, and wherein the secondary excitation state of the
selected radiation emitting material is a dark excitation
state.
[0052] 4. The method of aspect 1, wherein the primary excitation
state of the selected radiation emitting material is a slower
transition excitation state, and wherein the secondary excitation
state of the selected radiation emitting material is a faster
transition excitation state.
[0053] 5. The method of aspect 1, wherein the primary excitation
state of the selected radiation emitting material is a faster
transition excitation state, and wherein the secondary excitation
state is a slower transition excitation state.
[0054] 6. The method of aspect 1, wherein the primary excitation
state of the selected radiation emitting material emits a photon
with a horizontal polarization, and wherein the secondary
excitation state of the selected radiation emitting material emits
a photon with a vertical polarization.
[0055] 7. The method of any one of aspects 1 to 6, wherein applying
the primary radiation to the radiation emitting material comprises
applying ultraviolet radiation to the radiation emitting
material.
[0056] 8. The method any one of aspects 1 to 6, wherein applying
the primary radiation to the radiation emitting material comprises
applying visible radiation to the radiation emitting material.
[0057] 9. The method of any one of aspects 1 to 8, wherein applying
the secondary radiation to the thermal contribution material
comprises applying a single pulse of radiation to the thermal
contribution material.
[0058] 10. The method of any one of aspects 1 to 8, wherein
applying the secondary radiation to the thermal contribution
material comprises applying a series of pulses of radiation, with a
constant duty cycle, to the thermal contribution material.
[0059] 11. The method of any one of aspects 1 to 8, wherein
applying the secondary radiation to the thermal contribution
material comprises applying a series of pulses of radiation, with a
pulse repetition frequency that increases or decreases over time,
to the thermal contribution material.
[0060] 12. The method of any one of aspects 1 to 8, wherein
applying the secondary radiation to the thermal contribution
material comprises applying a series of pulses of radiation, with
an arbitrary pulse pattern, to the thermal contribution
material.
[0061] 13. The method of any one of aspects 1 to 12, wherein
applying the secondary radiation to the thermal contribution
material comprises applying infrared radiation to the radiation
emitting material.
[0062] 14. The method of any one of aspects 1 to 13, wherein the
radiation emitting material comprises a phosphor.
[0063] 15. The method of any one of aspects 1 to 14, wherein the
radiation emitting material comprises a molecular singlet.
[0064] 16. The method of any one of aspects 1 to 14, wherein the
radiation emitting material comprises a molecular triplet.
[0065] 17. The method of any one of aspects 1 to 16, wherein the
radiation emitting material comprises a III-V semiconductor
material.
[0066] 18. The method of any one of aspects 1 to 16, wherein the
radiation emitting material comprises a II-VI semiconductor
material.
[0067] 19. The method of any one of aspects 1 to 18, wherein the
radiation emitting material comprises a material with a
spin-forbidden transition state.
[0068] 20. The method of any one of aspects 1 to 19, wherein the
radiation emitting material comprises a quantum dot.
[0069] 21. The method of any one of aspects 1 to 19, wherein the
radiation emitting material comprises a nanocrystal.
[0070] 22. The method of any one of aspects 1 to 19, wherein the
radiation emitting material comprises a bulk material.
[0071] 23. The method of any one of aspects 1 to 22, wherein the
thermal contribution material comprises a ligand.
[0072] 24. The method of any one of aspects 1 to 23, wherein the
thermal contribution material comprises an organic material.
[0073] 25. The method of any one of aspects 1 to 24, wherein the
thermal contribution material comprises the same material as the
radiation emitting material.
[0074] 26. The method of any one of aspects 1 to 25, wherein the
thermal contribution material comprises a plurality of hydrocarbon
surface ligands.
[0075] 27. The method of any one of aspects 1 to 26, wherein the
thermal contribution material comprises a C1-50alkylene, wherein
the carbon backbone optionally has one or more heteroatoms selected
from O, NH, and S.
[0076] 28. An optical device comprising: a radiation emitting
material having a primary excitation state and a secondary
excitation state, wherein the primary and secondary excitation
states have different decay rates; a thermal contribution material
physically coupled to the radiation emitting material and
configured to provide thermal energy to the radiation emitting
material; a primary radiation source configured to supply primary
radiation to the radiation emitting material to excite the
radiation emitting material to the primary excitation state; and a
secondary radiation source configured to provide secondary
radiation to the thermal contribution material to generate thermal
energy in the thermal contribution material.
[0077] 29. The optical device of aspect 28, wherein the primary
excitation state of the radiation emitting material is a dark
excitation state, and wherein the secondary excitation state of the
radiation emitting material is a bright excitation state.
[0078] 30. The optical device of aspect 28, wherein the primary
excitation state of the radiation emitting material is a bright
excitation state, and wherein the secondary excitation state of the
radiation emitting material is a dark excitation state.
[0079] 31. The optical device of aspect 28, wherein the primary
excitation state of the radiation emitting material is a slower
transition excitation state, and the secondary excitation state of
the radiation emitting material is a faster transition excitation
state compared.
[0080] 32. The optical device of aspect 28, wherein the primary
excitation state of the radiation emitting material is a faster
transition excitation state, and the secondary excitation state of
the radiation emitting material is a slower transition excitation
state.
[0081] 33. The optical device of aspect 28, wherein the primary
excitation state of the radiation emitting material emits a photon
with a horizontal polarization, and wherein the secondary
excitation state of the radiation emitting material emits a photon
with a vertical polarization.
[0082] 34. The optical device of any one of aspects 28 to 33,
wherein the primary radiation source is configured to emit
ultraviolet radiation.
[0083] 35. The optical device of any one of aspects 28 to 33,
wherein the primary radiation source is configured to emit visible
radiation.
[0084] 36. The optical device of any one of aspects 28 to 35,
wherein the secondary radiation source is configured to emit a
single pulse.
[0085] 37. The optical device of any one of aspects 28 to 35,
wherein the secondary radiation source is configured to emit a
series of pulses with a constant duty cycle.
[0086] 38. The optical device of any one of aspects 28 to 35,
wherein the secondary radiation source is configured to emit a
series of pulses with a pulse repetition frequency that increases
or decreases over time.
[0087] 39. The optical device of any one of aspects 28 to 35,
wherein the secondary radiation source is configured to emit a
series of pulses with an arbitrary pulse pattern.
[0088] 40. The optical device of any one of aspects 28 to 39,
wherein the secondary radiation source is configured to emit
infrared radiation.
[0089] 41. The optical device of any one of aspects 28 to 40,
wherein the radiation emitting material comprises a phosphor.
[0090] 42. The optical device of any one of aspects 28 to 41,
wherein the radiation emitting material comprises a molecular
singlet.
[0091] 43. The optical device of any one of aspects 28 to 41,
wherein the radiation emitting material comprises a molecular
triplet.
[0092] 44. The optical device of any one of aspects 28 to 43,
wherein the radiation emitting material comprises a III-V
semiconductor material.
[0093] 45. The optical device of any one of aspects 28 to 43,
wherein the radiation emitting material comprises a II-VI
semiconductor material.
[0094] 46. The optical device of any one of aspects 28 to 45,
wherein the radiation emitting material comprises a material with a
spin-forbidden transition state.
[0095] 47. The optical device of any one of aspects 28 to 46,
wherein the radiation emitting material comprises a quantum
dot.
[0096] 48. The optical device of any one of aspects 28 to 46,
wherein the radiation emitting material comprises a
nanocrystal.
[0097] 49. The optical device of any one of aspects 28 to 46,
wherein the radiation emitting material comprises a bulk
material.
[0098] 50. The optical device of any one of aspects 28 to 49,
wherein the thermal contribution material comprises a ligand.
[0099] 51. The optical device of any one of aspects 28 to 50,
wherein the thermal contribution material comprises an organic
material.
[0100] 52. The optical device of any one of aspects 28 to 50,
wherein the thermal contribution material comprises the same
material as the radiation emitting material.
[0101] 53. The optical device of any one of aspects 28 to 52,
wherein the thermal contribution material comprises a plurality of
hydrocarbon surface ligands.
[0102] 54. The optical device of any one of aspects 28 to 53,
wherein the thermal contribution material comprises a
C1-50alkylene, wherein the carbon backbone optionally has one or
more heteroatoms selected from O, NH, and S.
* * * * *