JPH07232993A - Photochemical hole burning crystal and its production - Google Patents

Abstract

PURPOSE:To produce the hole burning crystal with which a stable hole burning is effected even at room temp. and a narrow line width of the hole can be attained by growing the crystal through melting and solidifying a mixture of fluoride or oxide of Sm with fluorides of K and La in a non-oxidizing atmosphere. CONSTITUTION:In the production of this hole burning crystal, fluoride or oxide of Sm and fluorides of K and La are mixed together in atomic ratios in the product crystal of Sm:K:La=x:(1-x+y):(1-y), wherein: 0.001<=x<=0.2; 0<=y<=x. The resultant mixture is melted and solidified at 1000 to 1500 deg.C in a non- oxidizing atmosphere to grow the crystal and to produce the objective irregularly structured fluorite type crystal which contains Sm<2+> as the guest optically active ion and in which the composition of the host is represented by the formula Smx: K1-x+yLa1-yF4 wherein (x) and (y) are as defined above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an irregular structure fluorite type crystal containing Sm ²⁺ , and more particularly to a photochemical hole burning material which can be used as a high density recording material.

[0002]

2. Description of the Related Art Photochemical hole-burning (PHB) materials have been attracting attention as recording elements that enable recording densities much higher than those of current optical disks. PH
In the B material, when the photoactive species as a crystal component is dispersed in an appropriate matrix in the material crystal, the photoactive species are placed at various sites, so that the light absorption spectrum of the crystal has a non-uniform spread. When a laser beam having a line width narrower than this spread is irradiated, only photoactive species that resonate with the light are excited.

Therefore, when the photoactive species of the PHB material are deactivated by a laser beam (writing operation), a sharp spectrum with a hole is present when measuring the absorption spectrum (reading). By making the presence or absence of this hole correspond to the digital information, it becomes possible to record at an extremely high density.

Initially, as a method of manufacturing such a PHB material, a method of doping an inorganic polymer or crystal with an organic molecule capable of expressing hole burning was developed. Recently, it has been proposed to dope rare earth ions as a substance capable of exhibiting hole burning, for example, BaFCl _0.5 Br.
_In the case of _0.5 : Sm ²⁺ crystal, it is reported that holes are formed at liquid nitrogen temperature (C.Wei, S.Haung et al, J.Lu.
minescence, Vol 143,161 (1989)). However, in this crystal, an extremely low operating temperature is required to develop the hole burning, and when the operating temperature is increased, the line width of the holes becomes large and the recording density of the recording element decreases.

Further, it has been reported that hole burning of SrFCl _0.5 Br _0.5 : Sm ²⁺ was observed at room temperature (R. Janniso and H. Bill, Europhys. Lett., Vol16,569 (19)).
91). However, this crystal can be obtained only in a small size of about 400 μm, which is not always practically sufficient in terms of easiness of production and size of material. Furthermore, when a second hole is formed adjacent to the first hole, a substantial part of the first hole is buried (so-called hole filling phenomenon).
Is observed, which is considered to be a problem in practical use.

Further, as a non-oxide glass, HfF ₄ ,
It has been reported that when a rare earth ion is contained in a fluoride glass such as BaF ₃ , hole burning is observed at room temperature (K. Hirao, S. Todoroki et al, J. Non-Cr.
yst. Solids. 152, 267 (1993). However, the hole is wide and it is considered that there is a problem in practical use.

On the other hand, it has been reported that borate glass containing divalent Sm ions as an oxide glass can be a stable hole-burning material at room temperature (K. Hirao, S. Todo).
roki et al, Opt. Lett. 18, 1586 (1993)). This material has a narrower hole line width than non-oxide, but it is still not sufficient in a practical sense.

At present, no bulk single crystal material has been found which exhibits hole burning at a temperature higher than liquid nitrogen temperature even at room temperature, has a sufficiently narrow hole line width, and has no hole filling phenomenon. .

[0009]

In view of the above situation, an object of the present invention is to provide a hole-burning crystal that stably exhibits hole-burning even at high temperature, for example, room temperature, and has a narrow hole line width. is there.

[0010]

As a result of various studies for solving the above-mentioned problems, the present inventors found that a certain fluorite type crystal containing Sm ²⁺ as a photoactive ion was found in the crystal. It has been found that Sm ²⁺ is a novel crystal that is stable, exhibits hole burning at a relatively high temperature of about room temperature, has a narrow hole line width, and has a high hole multiplicity. Further, they have found that this crystal can be obtained by melting and solidifying in a non-oxidizing atmosphere using a fluoride solid solution crystal having a highly disordered structure as a host, and completed the present invention.

That is, according to the present invention, Sm ²⁺ ions are contained as guest photoactive ions, and the host has the composition formula Smx: K.
_{1-x + y} La _1-y F ₄ (x: 0.001 ≦ x ≦ 0.2,
The present invention relates to a disordered structure fluorite type photochemical hole burning crystal represented by y: 0 ≦ y ≦ x) and a method for producing the same. Next, the present invention will be described in more detail.

In the crystal of the present invention, the amount of Sm ²⁺ as hole active ions is 0.0 as shown by x in the above composition.
Although 01 ≦ x ≦ 0.2, if this amount is less than 0.001, the absorption and emission intensity of crystals is weak, which is not preferable in terms of Hall characteristics, and if it is more than 0.2, concentration quenching occurs. It is not preferred because it will occur. Also, as shown in the above composition formula, the amount of y is unfavorable from the viewpoint of hole characteristics outside of this range, similar to x.

As a characteristic of the hole burning material for crystals of the present invention, Sm ²⁺ obtained by reduction has a property of being easily oxidized in the production method described later, but in the fluorite crystal of the present invention, Sm ²⁺ is present. Ions can be allowed to exist in a stable state, and crystals containing Sm ²⁺ are
High activation energy of photoionization and Sm after hole formation
^Since the ions that have changed to ³⁺ also exist in a stable state, excellent properties can be expected as an optical recording material that operates at room temperature among various hole burning materials.

Further, this disordered structure fluorite type crystal is an ionic bond form (Sm ion) of Sm ion and F ⁻ ion.
Since there are an extremely large number of portions where -F) is slightly different, the refractive index changes for each wavelength of light, so that a wavelength-multiplexed hologram can be obtained. Therefore, it can also be applied as a hologram multiple-recording material to which a photorefractive effect is applied. Can be expected. Next, the manufacturing method of the present invention will be described.

As a raw material for obtaining the crystal of the present invention, a fluoride or an oxide of each component constituting the crystal is used. That is, fluoride or oxide of Sm ion, K ion, La
Ion fluoride is used, and these are atomic ratio Sm: K:
La = x: 1−x + y: 1−y (0.001 ≦ x ≦ 0.
2, 0 ≦ y ≦ x), and the mixture is mixed in advance, and the mixture is mixed with a reducing gas such as hydrogen or a mixed gas of hydrogen and carbon dioxide or carbon monoxide, or carbon monoxide and carbon dioxide. Mixed gas, or a gas in which any of these gases is mixed with helium, argon, or nitrogen as a carrier gas, or melted and solidified in a non-oxidizing atmosphere using any of helium, argon, or nitrogen gas, and crystallized. To train.

The melting temperature in the crystal production method of the present invention is 100.
Slow cooling method of 0.1 to 0.5 ° C / min at 0 to 1500 ° C, or heat exchange method, pulling method with a growth rate of about 0.5 to 5 mm / hr, floating zone method, Bridgman method, etc. Are melted and solidified to obtain crystals.

[0017]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.

[Example 1] SmF ₂ , KF and LaF ₃ were prepared, mixed and molded so that the atomic ratio was Sm: K: La = 0.04: 1: 0.96, and the molded body was molybdenum crucible. And melted and solidified at 1350 ° C. in an argon gas atmosphere containing 2.5 vol% hydrogen to obtain a single crystal. The result of X-ray diffraction of the obtained crystal is shown in FIG. From the result of X-ray diffraction, the obtained crystal was a solid solution Sm: K having an irregular structure.
In the single crystal phase of LaF ⁴ , the lattice constant was a = 5.941A. The absorption spectrum of the obtained crystal is shown in FIG. The spectrum shows strong absorption due to the fd transition of Sm ²⁺ ,
It was confirmed to contain Sm ²⁺ .

The PHB of the obtained crystal was measured according to the following procedure. That is, the sample was irradiated with a DCM dye laser (about 100 mW) for 1 to 600 seconds at 293K.
Wavelength ⁵ D ₀ - was set to resonate to ⁷ F ₀ transition.
Intermittently performs irradiation then, ⁵ D ₀ - by monitoring emission at corresponding 720nm to ⁷ F ₂ transition, the excitation spectrum is observed, the excitation spectrum is excited with DCM dye laser with different wavelengths Was obtained.

FIG. 3 shows an excitation spectrum at room temperature after irradiation with a 682.5 nm DCM dye laser for 600 seconds. Permanently present hole burning in the spectrum was observed. The line width of the holes is about 5 cm ^-1 at room temperature, and by changing the wavelength, about 15 holes without hole filling are formed. The electron trap as a photochemical reaction product after hole burning is Sm ³⁺ , and the photochemical reaction is shown as Sm ²⁺ + (trap center) −> Sm ³⁺ + (trap center) ⁻ .

FIG. 4 shows the relationship between the hole burning time and the hole depth at room temperature. What was observed in Figure 3 is
So-called optical gate type (selective excitation wavelength λ ₁ and gate wavelength λ
₂ and λ ₁ = λ ₂ ) is not called. Therefore, if the gate wavelength is shortened, the hole burning efficiency can be improved or the burning time can be shortened.

[Example 2] SmF ₂ , KF and LaF ₃ were prepared and mixed so that the atomic ratio of Sm: K: La was 0.01: 0.99: 1. It was placed in a molybdenum crucible and heated and melted at 1350 ° C. in an argon gas atmosphere containing 2 vol% hydrogen, and a single crystal was grown by a slow cooling method. As for the grown crystal, as in Example 1, as a result of X-ray diffraction,
It was confirmed to be a single phase. Further, it was confirmed from the absorption spectrum measurement that Sm ²⁺ was contained.

The PHB of the obtained crystal was measured in Example 1
I went in the same way. After burning at room temperature, it was observed in the measured spectrum that holes were generated at room temperature. The line width of the holes is about 5 cm ^-1 at room temperature, and about 15 holes are formed.

Example 3 SmF ₂ , KF and LaF ₃ were prepared so that the atomic ratio Sm: K: La = 0.04: 1: 0.96 and mixed, and the mixture was used as a raw material to produce 1 vo.
Growth rate 1 mm / h under argon gas atmosphere containing l% hydrogen
The crystal was grown by the floating zone method. As a result of X-ray diffraction, the obtained crystal was confirmed to be a single phase. In addition, as a result of measuring an excitation spectrum after irradiation with a DCM dye laser, hole burning was observed at room temperature as in Examples 1 and 2.

[Example 4] SmF ₂ , KF and LaF ₃ were prepared, mixed and molded in an atomic ratio of Sm: K: La = 0.05: 0.95: 1, and the molded body was molybdenum crucible. In an argon gas atmosphere containing 2 vol% hydrogen so as to contain Sm ²⁺ ions by high-frequency induction heating, and the crystal rotation speed was 10 rpm and the pulling speed was 0.8.
20 mm diameter by pulling method in [100] axis direction at mm / h,
A single crystal having a length of 40 mm was grown. It was confirmed from the result of X-ray diffraction that the obtained crystal was a single phase.

It was confirmed from the absorption spectrum that this crystal contained Sm ²⁺ . The PHB was measured in the same manner as in Example 1. After laser irradiation, hole burning, which exists permanently at room temperature, was observed in the excitation spectrum.
The line width of the holes and the number of holes were almost the same as in Example 1.

Since there are many kinds of Sm-F bonds excited in different wavelengths of the laser in the above hole-burning crystal, the line width corresponding to the number of wavelengths can be changed by irradiating the laser with changing the wavelength. Holes can be formed.
Furthermore, an ITO film is attached to this hole burning crystal,
It has been found that when a voltage is applied to the ITO film, holes are formed for each wavelength of the laser, and holes are also formed for each wavelength of the laser even at voltages of other levels, which can serve as an optical multiple memory under an electric field. Further, by utilizing the characteristic that the hole width is narrow, it is possible to perform optical memory or signal processing and pattern recognition in the time domain using the photon echo phenomenon.

[0028]

INDUSTRIAL APPLICABILITY The disordered structure fluorite type crystal containing Sm ²⁺ of the present invention is a crystal containing other halogen (SrF).
Cl _0.5 Br _0.5 : Sm ²⁺ or Sm 2 ⁺ -containing HfF ₄ −
BaF ₂ type glass), borate glass, etc., have a narrower hole line width that appears in hole burning, and are obtained as crystals larger than other halides. Stable hole burning appears at room temperature, and room temperature operation is achieved. It can be expected as a material having excellent properties as an optical recording material.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction pattern of the crystal obtained in Example 1 of the present invention.

FIG. 2 is an absorption spectrum diagram of the crystal obtained in Example 1 of the present invention.

FIG. 3 is an excitation spectrum diagram of the crystal obtained in Example 1 of the present invention.

FIG. 4 is a diagram showing the relationship between the hole burning time and the hole depth of the crystal obtained in Example 1 of the present invention.

Claims (4)

[Claims] 1. A guest photoactive ion containing Sm ²⁺ ,
The host has the composition Sm _x : K _{1-x + y} La _1-y F ₄ (x: 0.
001 ≤ x ≤ 0.2, y: 0 ≤ y ≤ x) 2. The disordered fluorite type crystal according to claim 1, wherein the crystal is a hole burning crystal. 3. A fluoride or oxide of Sm, or a fluoride of K or La in an atomic ratio of Sm: K: La: in the produced crystal.
= X: 1−x + y: 1−y (x: 0.001 ≦ x ≦ 0.
2. A method for producing a disordered structure fluorite-type crystal, characterized by growing a crystal by melting and solidifying a mixture obtained by mixing in an amount ratio of y: 0 ≦ y ≦ x) in a non-oxidizing gas atmosphere. . 4. As the non-oxidizing gas, hydrogen, a mixed gas of hydrogen and carbon dioxide or carbon monoxide, a mixed gas of carbon monoxide and carbon dioxide, or one of these gases is helium or argon. 4. The manufacturing method according to claim 3, wherein a gas mixed with nitrogen, or any one of helium gas, argon gas, and nitrogen gas is used.