JP2618530B2 - New crystalline materials - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical crystal material having a novel crystal structure.
In particular, the present invention relates to a Bi (SrCa) O _x -based rare earth element-substituted compound crystal material.

[Problems to be Solved by Conventional Techniques and Inventions] There are two types of optical materials, that is, laser materials, from the viewpoint of light emission, that is, inorganic materials and organic materials. The inorganic optical materials are roughly divided into semiconductors and insulators (mainly oxides). As a typical example of the oxide laser material,
Ruby or YAG (Y ₃ Al ₅ O ₁₂ : yttrium aluminum
Garnet), but what they have in common is
That is, a small amount of a transition metal or a rare earth element is doped into the base oxide crystal. For example, Ruby has Cr ^{+ 3} ions at 0.
Al ₂ O ₃ containing about 05% and has a pink color.
In YAG, a small amount of Nd ³⁺ ions are added to the host crystal. In either case, when an appropriate external excitation is performed, the electrons in the doped ion are excited and relaxed between the spin and orbital levels, resulting in a sharp emission line at the energy position specific to the ion due to the inner shell transition. Present. The following is a comparison between a laser manufactured using an oxide laser material and a semiconductor laser that has made remarkable progress.

That is, a laser made of an oxide crystal material has advantages in that it can oscillate with a large output of several hundred watts, and that the oscillation wavelength does not depend on the operating temperature. Can oscillate at various wavelengths. However, lasers based on oxide crystal materials have disadvantages in comparison with lasers based on semiconductor materials, such as difficulty in downsizing because the excitation means is light irradiation, and low oscillation efficiency.

The present invention provides a novel optical crystal material that exhibits a light emitting function under appropriate external excitation in order to solve the technical disadvantages of the oxide crystal material when used as a laser material as described above. The purpose is to.

[Means for Solving the Problems] The gist of the present invention is a Bi (Sr, Bi, Sr, which has a rhombohedral crystal structure doped with a rare earth element and belongs to the Laue group m. Ca) _{Ox is} an insulating oxide crystal material.

According to the present invention, Bi is a novel substance as a host medium.
The most important point is to use (Sr, Ca) O _x compound crystals. A technique of substituting a small amount of a rare earth element in order to exhibit a light emitting function as a laser material is a conventional technique.

However, using a crystal material having a new crystal structure different from the conventional material as the matrix medium changes the crystal field around the doped ions, reflecting the difference in the crystal structure. This means that the level of the electron transition contributing to light emission and the oscillator strength are changed. Further, the strong structural anisotropy inherent to the present material further promotes the perturbation. The crystalline material of the present invention is different from the conventional crystalline material in that it has a revolutionary luminescent property, namely, transition energy,
Lifetime, luminous efficiency and the like are provided.

It is known that the Bi-based high-temperature superconductor greatly changes its superconductivity depending on the number of CuO planes contained in a unit cell. The present inventors have recognized from an early stage that studies using single crystals are indispensable in order to better understand high-temperature superconducting properties, and relatively large crystals can be easily obtained by the flux melting method. We have been studying single crystals of Bi-based superconductors to improve their quality. Among them, it has been found that an oxide crystal composed of Bi, Sr, and Ca containing no Cu can be obtained by charging a raw material at a constant cation ratio during crystal production. Further, the present inventors succeeded in introducing luminescence characteristics by performing local substitution of rare earth elements in the crystal.

As a result of structural analysis by the precession method, the obtained crystal belongs to the rhombohedral system regardless of the presence or absence of element substitution, and its c-axis length shows a positive correlation with the ionic radius of the substituted element. I understood that.

When the emission characteristics were examined by various excitation methods,
In the Er-substituted crystal, characteristic light emission due to inner-shell electron transition related to the substituted trivalent Er ion was observed.

In the Bi-Sr-Ca-Cu-O system, the existence of a superconductor having a critical temperature of 110K is known. When comparing the superconductor with the crystal of the present invention, the crystal of the present invention lacks Cu.
However, by using a process technology frequently used in the semiconductor field (for example, an ion implantation method or a thermal diffusion method), it becomes possible to introduce Cu into the crystal of the present invention and change the insulating region into a superconducting region. Come. This means that this Cu
It is interesting as a suggestion of the realization of a monolithic superconducting / optical integrated circuit provided by combining the superconductivity based on the introduced technology and the light emitting function of the crystal of the present invention.

The present invention has found a crystal exhibiting a light-emitting function under appropriate external excitation, and has an advantage that, for example, a characteristic laser or other such light-emitting block can be realized. Then, by using the selective introduction technique of Cu, a superconducting region can be locally formed, so that the superconducting element and the light emitting element are monolithically formed on the crystal material of the present invention, that is, The realization of an optical integrated circuit is possible.

Next, the crystal material of the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

[Examples] Crystal materials were prepared from oxides and carbonate powders as starting materials,
It was produced by a flux melting method. Cation ratio Bi: Sr: Ca: Cu
= 8: 1: 3: 3, the mixed powder was charged into an alumina crucible, melted at 1000 ° C for 24 hours, cooled to 700 ° C at a cooling rate of 5 ° C / hour, and further cooled at a rate of 40 ° C / In hours, 5
It was cooled to 00 ° C., and then cooled to room temperature in the furnace.

The doping of the rare earth element into the single crystal was performed by replacing two kinds of Er and Nd up to 11 atomic% of Ca in the charged composition.

The structure of the obtained single crystal was examined by an X-ray precession method. One of them is shown in FIG. 1B.

For the composition, use a microprobe electron microscope (EPM
Measured in A).

Emission characteristics in the visible region are cathodoluminescence (CL)
And photoluminescence (PL) method using argon laser as excitation source.

The obtained single crystal was a yellow (green) insulator regardless of the rare-earth element doping, and had a strong property of being cleaved thinly.

FIG. 1A is an electron micrograph of the Er-doped crystal surface of the present invention. This crystal is a crystal produced by a flux melting method, but can be produced without any problem by using other crystal growth techniques.

FIG. 1A suggests that it has a very flat surface, except for its cleavage step.

FIGS. 1B and 1C show a precession photograph taken with an undoped crystal and Miller indices of observed spots.
Here, the photograph of FIG. 1B is obtained when the X-ray incident direction k ₀ is perpendicular to the cleavage plane of the flaky crystal, that is, at the time of k ₀ <001>. The photo shows k ₀ ⊥ 〈001〉
It was obtained at the time. Taking into account the symmetry of the observed spots and that a certain relation (-h + k + 1 = 3n) is satisfied between their Miller indices (hkl),
It can be seen that the crystals of the present invention belong to the rhombohedral system. More specifically, it is a Laue crystal system and the possibility of m is high.

Similar results were obtained for the crystals to which the rare earth element was added. Table 1 compares and shows the lattice constants of various crystals obtained from the precession photographs.

Table 1 Lattice constants of various crystals a (Å) c (Å) not added 3.905 28.252 Er added 3.896 28.054 Nd added 3.928 28.116 Rare earth elements with small ionic radii at the time of crystal production (order of ionic radii: Er <Nd <Ca <Bi It can be seen that the c-axis length of the crystal obtained by adding <Sr) is reduced. This suggests that the added element is effectively replacing the crystal site.

FIG. 2 shows an X-ray diffraction spectrum of the crystalline material of the present invention.

Each broken peak is expressed by a hexagonal lattice using a defined lattice constant (a = 3.90 to 3.93 °, c = 28.05 to 28.25 °; varies depending on the type and amount of a rare earth element to be substituted).
Identified.

Table 2 shows the results of composition analysis of the cleavage planes of various crystals by the EPMA method (when the molar ratio of oxygen is also set to 5).

The measurement was performed twice for each crystal at different locations.
In the Nd-doped crystal, the location distribution of Nd is observed even though the production conditions are the same as those of the Er-doped crystal. However, in both cases of Er and Nd, it is clear that the rare earth element added to the raw material is incorporated in the crystal.

Note that this composition ratio is an example, and the above-described crystal structure can be obtained at other composition ratios.

As a result of examining each single crystal of the crystalline material of the present invention by a luminescence method, characteristic light emission in the visible region was observed in the Er-doped crystal.

FIG. 3 shows a CL image on a cleavage plane of a crystal of the present invention in which Er is substituted as a rare earth element. In addition to light emission from a uniform base, light emission with high local emission intensity and long life is observed. These are considered to be due to the flux remaining on the surface. FIG. 4 shows the result of observing the CL spectrum by focusing on the light emission from the base. Although the spectral resolution cannot be increased due to the measurement process, it cannot be obtained with the Er-doped crystal without the added crystal.
It can be seen that characteristic emission having a peak near 550 nm is observed.

A similar sample was examined by the PL method in order to perform spectrum measurement with higher resolution.

FIG. 5 shows a PL spectrum obtained from the Er-doped crystal.

According to this, when an argon laser having a wavelength of 488 nm was used as an excitation light source, two emission lines with fine structures at 544.7 nm and 555.7 nm were observed on the tail of the laser beam. These emission lines show that Er ⁺³ (4f
¹¹ ) It is caused by the electron transition between the spin and orbital levels of the ion. From the emission line on the short wavelength side, ² H _11/2 → ⁴ I _15/2 , ² S
_3/2 → ⁴ I Identified as _15/2 . These luminescence can be easily obtained by an electric excitation method.

[Effect of the Invention] The crystal material of the present invention has the following remarkable technical effects.

First, the present inventors have found crystals that exhibit a light-emitting function under appropriate external excitation. For example, there is an advantage that a light-emitting element such as a characteristic laser can be realized.

Second, the superconducting region can be locally formed by using the selective introduction technique of Cu. Therefore, the superconducting element and the light emitting element are monolithically formed on the crystal material of the present invention, that is, It is possible to realize a superconducting-optical integrated circuit.

[Brief description of the drawings]

FIG. 1A is an electron micrograph of the Er-doped crystal surface of the present invention. FIGS. 1B and 1C are X-ray precession photographs showing the crystal structure of the crystal without addition according to the present invention. FIG. 2 is an X-ray diffraction spectrum of the crystalline material of the present invention. FIG. 3 is a CL image on a crystal cleavage plane of the crystal material of the present invention. FIG. 4 is a graph showing an emission spectrum of the crystal material of the present invention in comparison with that of an unsubstituted host crystal. FIG. 5 is a PL spectrum obtained with the crystalline material of the present invention.

Claims (1)

(57) [Claims] The present invention is characterized in that it has a rhombohedral crystal structure doped with a rare earth element and belongs to the Laue group m.
Bi (Sr, Ca) O _x insulating oxide crystal material.