U.S. patent application number 11/106541 was filed with the patent office on 2005-08-18 for photochemical hole burning media.
This patent application is currently assigned to Osaka University. Invention is credited to Machida, Kenichi.
Application Number | 20050181307 11/106541 |
Document ID | / |
Family ID | 18917043 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050181307 |
Kind Code |
A1 |
Machida, Kenichi |
August 18, 2005 |
Photochemical hole burning media
Abstract
A photochemical hole burning medium is composed of a material in
which a rare earth complex and a reducing agent is dispersed in a
solid matrix. The rare earth complex may be at least one complex
selected from the group consisting of a europium (III) crown ether
complex, a europium (III) polyether complex, and a europium (III)
cryptand complex.
Inventors: |
Machida, Kenichi; (Minoo
City, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Osaka University
Suita City
JP
|
Family ID: |
18917043 |
Appl. No.: |
11/106541 |
Filed: |
April 15, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11106541 |
Apr 15, 2005 |
|
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10084480 |
Feb 28, 2002 |
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Current U.S.
Class: |
430/270.16 ;
G9B/7.013; G9B/7.142 |
Current CPC
Class: |
G11B 2007/24312
20130101; G11B 7/00453 20130101; G11B 7/2433 20130101; G11B 7/243
20130101; Y10S 430/146 20130101 |
Class at
Publication: |
430/270.16 |
International
Class: |
G11B 007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2001 |
JP |
2001-057113 |
Claims
What is claimed is:
1. A photochemical hole burning medium, comprising a material in
which a rare earth complex and a reducing agent dispersed in a
solid matrix, wherein the photochemical hole burning medium is used
at low temperatures; and said rare earth complex is at least one
complex selected from the group consisting of a europium (III)
crown ether complex, a europium (III) polyether complex, and a
europium (III) cryptand complex.
2. The photochemical hole burning medium set forth in claim 1,
wherein said rare earth complex and said reducing agent constitute
an electron-donating composite compound.
3. The photochemical hole burning medium set forth in claim 2,
wherein said electron-donating composite compound is a silane
compound or a disilazane compound.
4. The photochemical hole burning medium set forth in claim 3,
wherein said silane compound or the disilazane compound is a
hexaalkyl disilazane represented by hexamethyl disilane or a
hexaalkyldisilazane.
5. The photochemical hole burning medium set forth in claim 2,
wherein said electron-donating composite compound is an organic tin
compound.
6. The photochemical hole burning medium set forth in claim 1,
wherein said solid matrix is at least one glass-forming compound
selected from the group consisting of silica, germanium oxide,
boron oxide, phosphorus pentaoxide and tellurium oxide.
7. The photochemical hole burning medium set forth in claim 2,
wherein said solid matrix is at least one glass-forming compound
selected from the group consisting of silica, germanium oxide,
boron oxide, phosphorus pentaoxide and tellurium oxide.
8. The photochemical hole burning medium set forth in claim 3,
wherein said solid matrix is at least one glass-forming compound
selected from the group consisting of silica, germanium oxide,
boron oxide, phosphorus pentaoxide and tellurium oxide.
9. The photochemical hole burning medium set forth in claim 4,
wherein said solid matrix is at least one glass-forming compound
selected from the group consisting of silica, germanium oxide,
boron oxide, phosphorus pentaoxide and tellurium oxide.
10. The photochemical hole burning medium set forth in claim 5,
wherein said solid matrix is at least one glass-forming compound
selected from the group consisting of silica, germanium oxide,
boron oxide, phosphorus pentaoxide and tellurium oxide.
11. The photochemical hole burning medium set forth in claim 6,
wherein at least one compound selected from the group consisting of
Al.sub.2O.sub.3, Ga.sub.2O.sub.3, In.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is contained in said
solid matrix.
12. The photochemical hole burning medium set forth in claim 7,
wherein at least one compound selected from the group consisting of
Al.sub.2O.sub.3, Ga.sub.2O.sub.3, In.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is contained in said
solid matrix.
13. The photochemical hole burning medium set forth in claim 8,
wherein at least one compound selected from the group consisting of
Al.sub.2O.sub.3, Ga.sub.2O.sub.3, In.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is contained in said
solid matrix.
14. The photochemical hole burning medium set forth in claim 9,
wherein at least one compound selected from the group consisting of
Al.sub.2O.sub.3, Ga.sub.2O.sub.3, In.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is contained in said
solid matrix.
15. The photochemical hole burning medium set forth in claim 10,
wherein at least one compound selected from the group consisting of
Al.sub.2O.sub.3, Ga.sub.2O.sub.3, In.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is contained in said
solid matrix.
16. The photochemical hole burning medium set forth in claim 1,
wherein the reducing agent has an oxidation/reduction potential of
not more than 1 V.
17. The photochemical hole burning medium set forth in claim 2,
wherein the reducing agent has an oxidation/reduction potential of
not more than 1 V.
18. The photochemical hole burning medium set forth in claim 3,
wherein the reducing agent has an oxidation/reduction potential of
not more than 1 V.
19. The photochemical hole burning medium set forth in claim 4,
wherein the reducing agent has an oxidation/reduction potential of
not more than 1 V.
20. The photochemical hole burning medium set forth in claim 5,
wherein the reducing agent has an oxidation/reduction potential of
not more than 1 V.
Description
CROSS-REFERENCE
[0001] This is a Division of application Ser. No. 10/084,480 filed
on Feb. 28, 2002. The entire disclosure of the prior application is
hereby incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to optical memories for
wavelength multiple-type high density recording, and more
particularly the invention relates to optochemical hole burning
media.
[0003] Optical recording media in which recorded information can be
rewritten to another are broadly classified into the heat mode type
and the photon mode type according to the operating principles. In
the former, different states: (recorded state/erased state) which
are optically discernible from each other are reversely changed by
utilizing heating and cooling of the medium with irradiation of
laser beam. Magneto-optical media, phase transition media, organic
media, etc. belong to this type. In the photon mode type, an
intrinsic energy of a light determined by its wavelength is
directly used to cause reversible optical changes. Photochromic
media and optochemical hole burning (PHB) media belong to this
type.
[0004] The Persistent Spectral Hole Burning (PSHB) is the
phenomenon that when laser beam is irradiated upon a solid in which
molecules or ions having optical absorption ability, a hole
persistently appears in the spectrum at a wavelength equal to that
of the irradiated beam. The hole burning is an effective measure as
a high resolution spectroscopy for the solids, and is expected to
be applied as a wavelength-multiple type high density optical
memory in case that the width (uniform width) of the hole of the
hole is smaller than that (non-uniform width) of the absorption
spectrum. That is, when the hole burning is effected while the
wavelength of the irradiating laser, a plurality of holes
independent of one another can be formed in a single spot. If bids
of 1 and 0 are made correspondent to the presence and absence of
such a hole, the wavelength multiple recording is feasible, so that
optical memories at a super high density can be realized. As a
material for such an optical memory, materials into which rare
earth ions are introduced are known.
[0005] However, the media that are at a practical level or a near
practical level are of the heat mode type. In any of the optically
recording media of the heat mode type, recording is effected by
using a single-wavelength light, which poses a limit upon the
recording capacity.
[0006] On the other hand, the photon mode type is a level of
searching fundamental materials. Among the photon mode type optical
media, the optochemical hole burning media have the merit that the
recording capacity can be greatly increased by overwriting
information data at one location at different wavelengths. However,
the optochemical hole burning media are still at a level of
searching fundamental materials, including the above-mentioned rare
earth ion-introduced materials, and materials considered preferable
for the optochemical hole burning media are still at a study level.
Therefore, materials which can be used for the optochemical hole
burning media have been desired to be developed.
SUMMARY
[0007] Therefore, it is an object of the present invention to
provide optochemical hole burning media which can greatly increase
the recording capacity.
[0008] In order to accomplish the above object, the present
inventor repeatedly made strenuous studies on materials in which
various complexes were dispersed in a SiO.sub.2 matrix, and
consequently he discovered materials which can hold holes even at
room temperature.
[0009] The photochemical hole burning medium according to the
present invention comprises a material in which a rare earth
complex and a reducing agent are dispersed in a solid matrix.
[0010] The following are preferred embodiments of the photochemical
hole burning medium according to the present invention.
[0011] (1) The rare earth complex is at least one complex selected
from the group consisting of europium (III) crown ether complexes,
europium (III) polyether complexes, and europium (III) cryptand
complexes.
[0012] (2) The reducing agent is an electron-donating composite
compound. In this preferred embodiment of the optochemical hole
burning medium according to the present invention, the rare earth
complex contributing to the formation of the hole and the reducing
organic molecules contributing to the stabilization of the hole are
held in the form of an electron-donating composite compound in a
uniformly dispersed state.
[0013] (3) The electron-donating composite compound is a silane
compound or a disilazane compound.
[0014] (4) The silane compound is a hexaalkyl disilazane
represented by hexamethyl disilane, and the disilazane compound is
a hexaalkyl disilazane represented by hexamethyldisilazane.
[0015] (5) The electron-donating composite compound is an organic
tin compound.
[0016] (6) The organic tin compound is a compound represented by
RSnSnR in which R is an alkyl group or an aryl group.
[0017] (7) The solid matrix is at least one glass-forming compound
selected from the group consisting of silica, germanium oxide,
boron oxide, phosphorus pentaoxide and tellurium oxide.
[0018] (8) At least one compound selected from the group consisting
of Al.sub.2O.sub.3, Ga.sub.2O.sub.3, In.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 is contained in said
solid matrix.
[0019] These and other objects, features and advantages of the
invention will be appreciated upon reading of the following
description of the invention when taken in conjunction with the
attached drawings, with the understanding that any modifications,
variations and changes could be easily made by the skilled person
in the art to which the invention pertains.
[0020] As a further preferable embodiment of the photochemical hole
burning medium according to the present invention, the reducing
agent has an oxidation/reduction potential of not more than 1
V.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] For a better understanding of the invention, reference is
made to the attached drawings, wherein:
[0022] FIGS. 1(a) to 1(c) are graphs showing excitation spectra of
SiO.sub.2--ZrO.sub.2:[Eu(15C5)].sup.3+ before and after irradiation
with laser beams.
[0023] FIGS. 2(a) to 2(c) are graphs showing heat cycle
characteristics of SiO.sub.2--ZrO.sub.2: [Eu(15C5)].sup.3+ in which
FIGS. 2(a), 2(b) and 2(c) correspond to SiO.sub.2:ZrO.sub.2=7:3,
SiO.sub.2:ZrO.sub.2=5:5, and SiO.sub.2:ZrO.sub.2=3:7,
respectively.
[0024] FIGS. 3(a) and 3(b) are graphs showing fluorescent spectra
of SiO.sub.2:[Eu(15C5)].sup.3+ before and after laser beam
irradiation, respectively.
[0025] FIGS. 4(a) and 4(b) are graphs showing spectra of the
optochemical hole burning media according to an embodiment of the
present invention before and after laser beam irradiation,
respectively, in which FIGS. 4(a) and 4(b) correspond to
SiO.sub.2:Eu(15C5).sup.3+ Me.sub.3SiSiMe.sub.3 and
SiO.sub.2:Eu.sup.3+Me.sub.3SiSiMe.sub.3.
[0026] FIG. 5 is a graph showing spectra of the optochemical hole
burning medium of SiO.sub.2: Eu(15C5).sup.3+Me.sub.3SnSnMe.sub.3
according to another embodiment of the present invention before and
after laser beam irradiation.
[0027] FIGS. 6(a) to 6(c) are graphs showing heat cycle
characteristics of optochemical hole burning media a further
embodiment according to the present invention in which FIG. 6(a)
shows the heat cycle characteristic of
SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SiSiMe.sub.3, and FIGS. 6(b) and
6(c) show the heat cycle characteristics of
SiO.sub.2:Eu(15C5).sup.3+ Me.sub.3SnSnMe.sub.3 and SiO.sub.2:
Eu(15C5).sup.3+, respectively.
[0028] FIGS. 7(a) and 7(b) are graphs showing heat cycle
characteristics of optochemical hole burning media with
SiO.sub.2:Eu(15C5).sup.3+Me.sub.3- SiSiMe.sub.3 of other embodiment
according to the present invention in which FIG. 7(a) shows the
heat cycle characteristics of in the use of 3 mol %
Me.sub.3SiSiMe.sub.3 for SiO.sub.2
Eu(15C5).sup.3+Me.sub.3SiSiMe.su- b.3, and FIGS. 7(b) the heat
cycle characteristic in the use of 6% Me.sub.3SiSiMe.sub.3 for
SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SnSnMe.sub.3.
[0029] FIGS. 8(a) to 8(d) are graphs showing excitation spectra of
SiO.sub.2:M.sub.xO.sub.y
(Si:M=7:3):[Eu(15C5)].sup.3+(Eu.sup.3+:15C5=1:3) at 77K before and
after laser irradiation.
[0030] FIGS. 9(a) and 9(b) are graphs showing heat cycle
characteristics of hole burning media of the
SiO.sub.2:M.sub.xO.sub.y:[Eu(15C5)].sup.3+ media irradiated at
77K.
[0031] FIGS. 10(a) and 10(b) are graphs showing heat cycle
characteristics of hole burning media of
SiO.sub.2:M.sub.xO.sub.y:[Eu(15C5)].sup.3+ at 77K.
[0032] FIG. 11 shows excitation spectra of
SiO.sub.2:Eu(15C5).sup.3+C.sub.- 9H.sub.8 (indene) before and after
irradiation with laser at 77 K and a differential spectrum
therebetween.
DETAILED DESCRIPTION
[0033] The photochemical hole burning medium according to the
present invention comprises a material in which a rare earth
complex and a reducing agent dispersed in a solid matrix. That is,
the present invention is directed to the optochemical hole burning
medium using the material exhibiting the optochemical hole burning
phenomenon.
[0034] In the present invention, the term "solid matrix" means host
molecules of the optochemical hole burning medium, and is not
particularly limited. For example, as the solid matrix, at least
one glass-forming compound selected from the group consisting of
silica, germanium oxide, boron oxide, phosphorus pentaoxide and
tellurium oxide may be recited. Further, at least one compound
selected from the group consisting of Al.sub.2O.sub.3,
Ga.sub.2O.sub.3, In.sub.2O.sub.3, ZrO.sub.2, Nb.sub.2O.sub.5 and
Ta.sub.2O.sub.5 may be contained in the solid matrix. From the
standpoint of easy productibity with use of a sol-gel method,
silica may be recited as the solid matrix.
[0035] As the rare earth complex, at least one complex selected
from the group consisting of a europium (III) crown ether complex,
a europium (III) polyether complex, and a europium (III) cryptand
complex may be recited.
[0036] In view of the fact that easy reduction from trivalent to a
divalent state, which is considered to be a factor of inducing the
optochemical hole burning effected, the europium (III) crown ether
complex is preferred as the rare earth complex. As large ring
compounds represented by the crown ether, large ring compounds
having heteroatoms such as oxygen, nitrogen, sulfur, etc., e.g.,
12-crown-4, 15-crown-5, 18-crown-6, 24-crown-8, dibenzo-18-crown-6,
cryptand[2,2], cryptand [2,2,2], etc., may be recited. In the
present invention, such large ring compounds may be recited.
[0037] From the standpoint of easy complex formation of divalent
europium ions, 15-crown-5 (hereinafter referred to as "15C5") is
preferred as the crown ether.
[0038] The rare earth metals are not particularly limited, and Eu,
Sm, Pr, etc. may be recited. From the easy complex formation of
divalent europium ions, Eu may be recited as the rare earth
element.
[0039] The reducing agent used in the present invention is not
particularly limited so long as it can readily reduce the rare
earth ions while not causing a reverse reaction and its absorption
does not overlap with that of a zerophone line of the rare earth
ions. Preferably, organic molecular compounds which exhibit
compatibility with the rare earth complex may be recited. From the
standpoint of easy transportation of electrons with the rare earth
ions, the reducing agent may be an electron-donating composite
compound. As the electron-donating composite compound, a silane
compound, a disilazane compound or the organic tin compound may be
recited.
[0040] As the silane compound, at least one a hexaalkyl disilazane
represented by hexamethyl disilane may be recited. As the
disilazoneor, a hexaalkyldisilazane represented by hexamethyl
disilazane may be recited. From the standpoint of being readily
dissolved in a common solvent to be used in the sol-gel reaction,
hexamethyl disilane and disilazane compound may be recited as the
silane compound and the disilazane compound, respectively.
[0041] As the electron-donating composite compound, an organic tin
compound may be used. As the organic tin compound, a compound
represented by RSnSnR in which R is an alkyl group or an aryl group
may be recited. From the standpoint of being readily dissolved in a
common solvent to be used in the sol-gel reaction, R is preferably
a methyl group.
[0042] The use amount of the reducing agent varies depending upon
rare earth ions, complex ligands, solid matrixes, etc. as employed,
and is not particularly limited. From the standpoint of maintaining
the high hole stability, up to 20 mol % of the reducing agent may
be used relative to the entire amount of the metal component
constituting the solid matrix. The use amount is preferably 3 to 6
mol % from the standpoint of the transparency and light
transmission of the medium.
[0043] According to a further preferable embodiment of the
photochemical hole burning medium of the present invention, the
reducing agent has an oxidation/reduction potential of not more
than 1.5 V (vs. SCE). The reason is that the oxidation potential of
E.sup.3+/Eu.sup.2+ is about -0.43 V (vs. NHE), the Eu is converted
to an excited state by irradiation with laser beam, and Eu.sup.3+
can be reduced to Eu.sup.+2, if the oxidation/reduction potential
is not more than 1.5 V (vs. SCE).
[0044] Therefore, any reducing organic molecule having the
oxidation/reduction potential of not more than 1.5 V (vs. SCE) as
the reducing agent can theoretically reduce Eu.sup.3+ to Eu.sup.2+
and can exhibit the hole burning effect.
[0045] Even other organic molecules having an oxidation/reduction
potential of more than 1.5 V (vs. SCE) can cause hole in relation
to other rear earth complex. In such a case, the organic molecules
having the oxidation/reduction potential of more than 1.5 V (vs.
SCE) can be used.
[0046] Next, the method for producing the optochemical hole burning
medium according to the present invention will be explained. The
optochemical hole burning medium according to the present invention
can be produced by using the ordinary sol-gel method, for example.
The sol-gel method is generally a method in which a gel is obtained
by dewatering a hydroxide-containing sol, and an inorganic oxide or
the like having a given shape or in the form of a thin or thick
film on a substrate is prepared by heating and drying the gel.
EXAMPLES
[0047] The present invention will be explained in more detail with
reference to specific Examples, but the invention is never intended
to be interpreted as being limited to these Examples.
Example 1
[0048] An optochemical hole burning medium using a solid matrix in
which SiO.sub.2 was added to ZrO.sub.2 was prepared by the sol-gel
method. The preparing procedure was as follows. A few or several
drops of hydrochloric acid were added as a catalyst into a solution
of Si(OC.sub.2H.sub.5).sub.4:H.sub.2O:C.sub.2H.sub.5OH=1:1:5 (molar
ratio), which was refluxed for one hour. Then, a metal alkoxide:
Zr(OC.sub.2H.sub.5).sub.4 was added to the resulting solution such
that Si:Zr=7:3, 5:5 or 3:7, followed by one hour refluxing.
EuCl.sub.3:H.sub.2O:C.sub.2H.sub.5OH=0.03:4:4:0.03 was added to the
resultant, which was subjected to drying at 50.degree. C. for 2
weeks or 90.degree. C. for 2 days. Thereby,
(SiO.sub.2--ZrO.sub.2):[Eu(15C5)].sup.- 3+ was obtained.
[0049] After the resulting sample was cooled by using a cryostat, a
hole was formed through being irradiated with laser beam of
rhodamine 6G colarant at 100 mW/mm.sup.2 for 10 minutes. The
stability of the hole was evaluated based on temperature cycles
that the sample having a hole formed at 77K was heated to a given
temperature, held at this temperature for about 1 minutes and
cooled again to 77K.
[0050] More specifically, the hole was formed by irradiating laser
beam at 77K upon each of samples in which 3 mol % of EuCl.sub.3 and
9 mol % of 15-crown-5(15C5) were incorporated into a ceramic
material formed by mixing SiO.sub.2 with ZrO.sub.2 at a given
ratio.
[0051] FIGS. 1(a), 1(b) and 1(c) show excitation spectra of
.sup.7Fo-.sup.5Do before and after the laser irradiation upon these
samples.
[0052] As a result, it was seen that as the content of ZrO.sub.2 in
the solid matrix increased, the non-uniform width was enlarged.
Thus, it is considered that the local structure near Eu.sup.3+ ions
in the matrix became non-uniform due to the incorporation of
ZrO.sub.2. However, the depth of the hole formed decreased with
increase in the incorporated amount of ZrO.sub.2. Further, an
anti-hole was seen in the case of SiO.sub.2:ZrO.sub.2=5:5. This is
interpreted such that the formation of a complex between Eu.sup.3+
ions and 15C5 was interrupted by the formation of a firm
network.
[0053] FIGS. 2(a), 2(b) and 2(c) show heat cycle characteristics of
(SiO.sub.2--ZrO.sub.2):Eu(15C5).sup.3+ each having a hole formed at
77K. FIG. 2(a) corresponds to SiO.sub.2:ZrO.sub.2=7:3, FIG. 2(b) to
SiO.sub.2:ZrO.sub.2=5:5, and FIG. 2(c) to
SiO.sub.2:ZrO.sub.2=3:7.
[0054] When the ingredients constituting the matrix were
SiO.sub.2:ZrO.sub.2=7:3, the hole could be maintained up to 300K.
When the ingredients constituting the matrix were SiO.sub.2:
ZrO.sub.2=5:5, the hole could be maintained up to 150K. When the
ingredients constituting the matrix were SiO.sub.2: ZrO.sub.2=5:5,
the hole could be maintained up to 100K. This revealed that if the
ZrO.sub.2 is added at a high concentration, the hole-forming
efficiency decreases and the hole cannot be maintained at high
temperatures, although the non-uniform width increases.
Example 2
[0055] Next, in order to clarify a cause for the high
hole-maintaining temperatures of the above-mentioned composite
glasses, R6G laser beams at an intensity of 300 mW/mm.sup.2 and a
wavelength of 579.6 mm were irradiated upon
SiO.sub.2:Eu(15C5).sup.3+(EuCl.sub.3=3 mol %, 15C5=9 mol %) at room
temperature for 2 hours, and fluorescent spectra were examined
before and after the irradiation. Results of the fluorescent
spectra are shown in FIGS. 3(a) and 3(b). As a result, it was
clarified in the laser-irradiated samples that the intensity of
light emission at 570.about.720 nm based on Eu.sup.+3 ions
decreased, whereas fluorescent peak based on Eu.sup.+2 ions newly
appeared at around 420 nm.
[0056] From the above, it was suggested that the optical reduction
from Eu.sup.3+ ions to Eu.sup.2+ ions was caused as the PSHB
mechanism by the laser irradiation.
Example 3
[0057] From the results stated in Example 2, it was clarified that
the reduction from Eu.sup.3+ to Eu.sup.2+ can exhibit excellent
hole-maintaining characteristic.
[0058] Thus, various reducing agents were dispersed in trial into
solid matrixes together with rare earth complexes.
[0059] First, tests were performed with a silane compound being
used as a reducing agent. More specifically,
SiO.sub.2:Eu(15C5).sup.3+, Me.sub.3SiSiMe.sub.3 was prepared. The
preparing procedure was as follows. A few or several drops of
hydrochloric acid were added as a catalyst into a solution of
Si(OC.sub.2H.sub.5).sub.4:H.sub.2O:C.sub.2H.s- ub.5OH=1:1:5 (molar
ratio), which was refluxed for one hour. Then,
EuCl.sub.3:H.sub.2O:C.sub.2H.sub.5OH:15C5:Me.sub.3=0.03:4:4:0.03:0.06
(molar ratio) were added to the resulting solution, which was
subjected to drying at 50.degree. C. for one week or at 90.degree.
C. for 2 days. Thereby, SiO.sub.2:Eu(15C5).sup.3+,
Me.sub.3SiSiMe.sub.3 was obtained. Loaded compositions for typical
glass materials are shown in Table 1.
1TABLE 1 Loaded composition for the typical glass materials TEOS
(1:1:5) Me.sub.3SiSiMe.sub.3 reflux liquid EuCl.sub.3 H.sub.2O
C.sub.2H.sub.5OH 15-crown-5 (molar ratio) 1 0.03 4 4 0.03 0.06 1
0.03 4 4 0 0.06 TEOS (1:1:5) reflux liquid EuCl.sub.3 H.sub.2O
C.sub.2H.sub.5OH 15-crown-5 Me.sub.3SiSiMe.sub.3 1 0.03 4 4 0.03
0.03 1 0.03 4 4 0 0.03
[0060] Samples to which neither Me.sub.3SiSiMe.sub.3 nor the crown
ether was added were prepared in the same manner.
[0061] In the same manner as mentioned above,
SiO.sub.2:Eu(15C5).sup.3+, Me.sub.3SnSnMe.sub.3 was obtained.
[0062] With respect to the hole burning characteristic, a holes was
formed by using rhodamine 6G colarant laser. Heat cycle tests were
effected such that after the hole was formed at 77K, then the
temperature was successively raised to 100K, 150K, 200K, 250K and
300 K, the temperature of 300K was maintained for about 1 minute
and returned to 77K again, and an excitation spectrum was
measured.
[0063] FIGS. 4(a) and 4(b) show excitation spectra and differential
spectra of SiO.sub.2:Eu(15C5).sup.3+, Me.sub.3SiSiMe.sub.3 and
SiO.sub.2: Eu(15C5).sup.3+, Me.sub.3SnSnMe.sub.3 before and after
the laser irradiation at 77K, respectively.
[0064] An excitation spectrum corresponding to .sup.7Fo-5Do
transition of Eu.sup.3+ ions in a wavelength range of 579 to 581 nm
was observed in the samples not irradiated. When the rhodamine 6G
colarant laser was irradiated upon these samples at a rate of 100
mW/mm.sup.2 for 600 seconds, a half-value width of 0.125 nm was
observed as shown in FIGS. 4(a) and 4(b).
[0065] In the sample with no crown ether added, no hole was formed,
although the intensity of the light emission over the entire
spectrum merely decreased through being irradiated with the laser.
This revealed that as compared with the Eu.sup.3+ ions alone, the
Eu.sup.3+ ions forming a complex with the crown ether more readily
receive electrons from in the matrix Me.sub.3SiSiMe.sub.3 when in
the erected state, so that they can more effectively form the
hole.
[0066] Spectra were observed with respect to
SiO.sub.2:Eu(15C5).sup.3+ and Me.sub.3SnSnMe.sub.3. FIG. 5 shows an
excitation epectrum and a differential spectrum of
SiO.sub.2:Eu(15C5).sup.3+, Me.sub.3SnSMe.sub.3 at 77K before and
after the laser irradiation.
[0067] As a result, the formation of hole was confirmed with
respect to Me.sub.3SnSnMe.sub.3 to which the crown ether was
incorporated (half-value width 0.141 nm). With respect to the
sample containing no crown ether, no hole was formed. Therefore, it
was clarified that as compared with the Eu.sup.3+ ions alone, the
Eu.sup.3+ ions forming a complex with the crown ether more readily
receive electrons from Me.sub.3SnSnMe.sub.3 in the matrix when in
the erected state, so that they can more effectively form the
holes.
Example 4
[0068] Next, the heat cycle characteristic was examined with
respect to an optochemical hole burning medium according to one
embodiment of the present invention.
[0069] First, SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SiSiMe.sub.3,
SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SnSnMe.sub.3 and
SiO.sub.2:Eu(15C5).sup.- 3+ were prepared. SiO.sub.2
Eu(15C5).sup.3+Me.sub.3SnSnMe.sub.3 was prepared in the same manner
as in Example 3 except that Me.sub.3SnSnMe.sub.3 was used instead
of Me.sub.3SiSiMe.sub.3. Further, SiO.sub.2: Eu(15C5).sup.3+ was
prepared in the same manner as in Example 3 except that no
electron-donating composite compound was used.
[0070] With respect to these samples, the heat cycle characteristic
was examined. That is, the heat cycle characteristic of a hole
formed at 77K in each of the SiO.sub.2,
Eu(15C5).sup.3+Me.sub.3SiSiMe.sub.3 and
SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SnSnMe.sub.3 in a temperature
range of 77 to 300K were examined. Results are shown in FIGS. 6(a)
to 6(c). FIG. 6(a) shows a heat cycle characteristic of
SiO.sub.2:Eu(15C5).sup.3+ Me.sub.3SiSiMe.sub.3, and FIGS. 6(b) and
6(c) shows heat cycle characteristics of
SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SnSnMe.sub.3 and SiO.sub.2
Eu(15C5).sup.3, respectively.
[0071] In the SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SiSiMe.sub.3, the
hole was maintained up to 300K. In the
SiO.sub.2:Eu(15C5).sup.3+Me.sub.3SnSnMe.sub- .3, the hole was
maintained up to 250K.
[0072] With increase in temperature, the uniform width increases,
whereas the depth of the holes decreases. When the sample contains
Me.sub.3SiSiMe.sub.3, the holes having about 70% of that of the
holes at 77K with the half-value width of 0.479 nm was maintained
at 300K. When the sample contains Me.sub.3SnSnMe.sub.3, the hole
having about 61% of that of the hole at 77K with the half-value
width of 0.474 nm was maintained at 250K. Therefore, it is seen
that the medium to which the reducing agent is added has improved
temperature stability of the hole as compared with the crown ether
complex alone. This is considered such that when Me.sub.3MMMe.sub.3
(M=Si or Sn) functioning as the reducing agent is incorporated, the
M-M bond is cleaved through the reduction to make a reverse
reaction difficult to occur.
Example 5
[0073] Next, the heat cycle characteristic was examined while the
concentration of the reducing agent was varied. Samples were
prepared according to the method described in Example 3.
Me.sub.3SiSiMe.sub.3 was used as the reducing agent.
[0074] Results on the heat cycle characteristic are shown in FIGS.
7(a) and 7(b). FIGS. 7(a) and 7(b) show the heat cycle
characteristics of SiO.sub.2 Eu(15C5).sup.3+Me.sub.3SiSiMe.sub.3 in
which FIGS. 7(a) and 7(b) correspond to uses of 3 mol % and 6 mol %
of Me.sub.3SiSiMe.sub.3, respectively.
[0075] As obvious from FIGS. 7(a) and 7(b), it is seen that the
case using 6 mol % of Me.sub.3SiSiMe.sub.3 exhibited higher
stability of the hole as compared with the case using 3 mol % of
Me.sub.3SiSiMe.sub.3. This is considered such that increase in
Me.sub.3SiSiMe.sub.3 increased the amount of Eu(15C5).sup.3+, so
that the holes became difficult to return correspondingly.
Example 6
[0076] Next, spectra were examined when the solid matrix was
modified. Solid matrixes in which Al.sub.2O.sub.3, TiO.sub.2 or
Ta.sub.2O.sub.5 was incorporated into SiO.sub.2 were used. Samples
were prepared similarly according to the method described in
Example 1.
[0077] Laser were irradiated upon each of these samples, and their
excitation spectra were observed. FIGS. 8(a) to 8(d) show
excitation spectra of SiO.sub.2-M.sub.xO.sub.y
(Si:M=7:3):[Eu(15C5).sup.3+].sup.3+ (Eu.sup.3+:15C5=1:3) at 77K
before and after laser irradiation.
[0078] In each of the cases, the depth of the hole was not
conspicuously different from that in the case with SiO.sub.2
alone.
[0079] With respect to the width of the hole, when Al.sub.2O.sub.3
was introduced into SiO.sub.2, Al.sup.3+ bonds to non-crosslinking
oxygen to form a network as [AlO.sub.4]. Thereby, the local
structure near the Eu.sup.3+ ions is strengthened to narrow the
width of the hole. It is considered that similar effect is produced
in the case of the incorporation of ZrO.sub.2 and
Ta.sub.2O.sub.5.
[0080] To the contrary, when TiO.sub.2 was incorporated into
SiO.sub.2, the hole width tended to increase as compared with
SiO.sub.2. This is considered that [TiO.sub.4] bonds to the
crosslinking oxygen rather than non-crosslinking oxygen.
[0081] Next, the heat cycle characteristic of the above samples was
examined. FIGS. 9 and 10 show the heat cycle characteristics of
holes formed at 77K in SiO.sub.2-MxOy:[Eu(15C5)].sup.3+.
[0082] In each case, the hole was confirmed after the heat cycles
down to room temperature. Particularly, the incorporation of
ZrO.sub.2 and Ta.sub.2O.sub.5 retained deeper holes at room
temperature as compared with Al.sub.2O.sub.3.
[0083] Any of the solid matrixes used exhibited high stability of
the holes at high temperatures. This is considered such that the
local structure near the Eu.sup.3+ ions was strengthened and the
lattice vibration was suppressed by the addition of the heavy
element.
[0084] The hole burning medium according to the present invention
has the advantageous effect that signals can be written therein
depending upon the wavelength of the laser beam irradiated.
Example 7
[0085] A photochemical hole burning medium was prepared in the same
manner as in Example 1, and tested in the same manner as in Example
3 except that indene was used as a reducing agent.
[0086] FIG. 11 shows excited spectra of SiO.sub.2:Eu(15C5).sup.3+,
indene before and after irradiation with laser at 77 K and a
differential spectrum therebetween.
[0087] As a result, formation of a hole was confirmed. From this
result, it is seen that any reducing agent can well function as the
reducing agent and form a stable hole, so long as its
oxidation/reduction potential is equal to or lower than that of
indene. The oxidation/reduction potentials of organic molecules are
summarized in below Table 2.
2 TABLE 2 reducing agents E.sup.0(D.sup.+/D)
N,N,N,N-tetramethyl-p-phenylene diamine 0.16 N,N,N,N-tetramethyl
benzidine 0.32 1,4-diazabicyclo[2,2,2]octane 0.57 hexamethyl ditin
0.68 N,N-dimethylaniline 0.76 hexamethyl disilane 0.92
Triethylamine 0.96 2-methoxynaphthalene 1.42 1,1-diphenylethylene
1.52 Indene 1.52
[0088] It is seen that the reducing agents shown in Table 2 all
have the oxidation/reduction potentials lower than that of indene,
and are well used.
[0089] The hole burning medium according to the present invention
has the advantageous effect that it enables the wavelength-multiple
type optical memory operable at room temperature.
* * * * *