Tetsuhiko Tomiki

Optical Spectra of Y2O3 Single Crystals in VUV

Optical absorption in the tail region and reflectivity at room temperature in the VUV region up to 42 eV are measured on Y 2 O 3 single crystals. Various optical constants as functions of photon energy are derived therefrom by use of the Kramers-Kronig relation. The Urbach rule parameters are also determined experimentally for the tail. A tentative interpretation is given on the spectral structures found in the optical constants, referring to the energy levels of Y 2+ and Y 3+ free ions.

Studies on the Preparation of Pure Alkali Chlorides

Systematic studies were made on the preparation of pure KCl and NaCl crystals. Effects of the starting material on the purity of crystal were studied with KCl and NaCl powders of reagent grade of several different brands and with those prepared from bicarbonate and hydrochloric acid. Methods by distillation and crystallization in vacuum and by Kyropoulos technique in air were used for the crystallization procedures to study on each of their advantages. To estimate the concentration of impurities in crystals, the measurement of ionic conductivity was made for multivalent metallic ions, optical absorption for hydroxyl ions, and chemical analysis for bromine ions. The purest crystal in respect of these impurities was found to be the one grown from its powder prepared from bicarbonate and hydrochloric acid by the method of distillation and crystallization in vacuum. After the studies on the edge of the fundamental absorption in connection with the concentration of bromine, an absorption band due to the presen...

Optical Constants and Exciton States in KCl Single Crystals. I. The Low Temperature Properties

Optical measurements were carried out on the reflectivity and absorption tails of KCl single crystals over the region 6.0 to 12 ev in the temperature range 10 to 573°K. With use of these data, Kramers and Kronig analysis was made on reflectivity spectra for three different temperatures 10, 78 and 295°K. The analysed spectra of important optical constants are presented in this article, and their properties are discussed in order to clarify the excitonic picture in a single crystalline lattice. The result is analysed along the theories of Toyozawa and Elliot. It was found that the first exciton line shape and the plateau in the higher energy side of the step are explained by them. The two overlapping components of the first band can be well separated at low temperatures in the case of single crystals, and this permits us to determine an oscillator strength for each component as 0.27 and 0.375 for \(\left(\frac{3}{2},\frac{1}{2}\right)\)- and \(\left(\frac{1}{2},\frac{1}{2}\right)\)-transition, respectively....

Ce3+ Centres in Y3Al5O12 (YAG) Single Crystals. II

The absorption spectra due to the 4 f →5 d transitions in Ce 3+ centres have been measured with the use of YAG:Ce 3+ single crystals with a lattice concentration [Ce 3+ ] L =(1.28±0.05)%. The data are almost independent of the spectral behaviour of a reference spectrum whose absorption constants are ∼2 cm -1 at the highest, since the absorption constants of 129 cm -1 and 50 cm -1 have been derived, relative to the reference spectrum, at the strongest peaks in the dγ and d e regions, respectively. The absorption area 32.3 cm -1 eV measured on the strongest dγ-band suggests that about a quarter of the Ce-concentration, [Ce 3+ ] M , added in the mixture of the starting powders is incorporated into [Ce 3+ ] L as YAG:Ce 3+ . It is found that the highest-energy lying d e band is located at 6.06 eV, in agreement with 6.07 0 eV for the corresponding band peak in the excitation spectrum and that the ratio of the absorption area of dγ to that of d e is nearly 2:3.

Temperature Dependence of the Fundamental Spectra of Potassium-Halides in the Schumann Ultraviolet Region (4.4∼13.5 eV)

The spectra of reflectivity R ( E ), dielectric constant e 2 ( E ) and loss Im \(\hat\varepsilon(E)^{-1}\) in the fundamental region of K-halides, measured at room and low temperatures, are presented. The line-shape parameters for the Γ-excion lines are determined as a function of temperature for KF, KBr and KI. The presence of the LO-phonon sideband is is confirmed on all the K-halides except KF. The antiresonance dip found in the continuum region of the lowestenergy Γ-excion of KI is interpreted in terms of the excion-continuum interaction proposed by Onodera. Considerations are given on the uncertainties in the line-shape parameters which are due to the errors of the absolute megnitude of R ( E ) and also due to the approximation procedures in the Kramers-Kronig analysis.

Optical Constants and Exciton States in KCl Single Crystals. II. The Spectra of Reflectivity and Absorption Constant

The reflectivity between 6 eV and 12 eV and the absorption tails both in the intrinsic region and in the impurity bromine band region of KCl single crystals are studied as a function of temperature in the range 10°K to 573°K. The absorption measurement complements the earlier results reported in 1960 1) and 1961 2) in improving the wavelength scale and in extending the temperature range. The present data allow us to investigate the phonons interacting with \(\varGamma\)-exciton, yielding \(\hbar\omega{=}1.42{\times}10^{-2}\) eV (for (3/2, 1/2-component)) and =1.59×10 -2 eV (for (1/2, 1/2)-component)) for phonons effective to the peak shift and \(\hbar\omega{=}1.47{\times}10^{-2}\) eV for phonons taking part in the optical absorption processes in the intrinsic Urbach tail. The temperature dependence is presented on the absorption constant spectra up to 12 eV and dispersion spectra n up to the \(\varGamma\)-exciton region, each being derived by the Kramers and Kronig analysis with the use of the above data....

Optical Studies of NaCl Single Crystals in 10 eV Region II. The Spectra of Conductivity at Low Temperatures, Absorption Constant and Energy Loss

Kramers-Kronig analysis was made on the reflectivity spectra of NaCl single crystals in the region 6eV to 12eV for temperature range from 10°K to 573°K. The spectra of absorption constant and energy loss are reported for the temperature range from 10°K to 573°K and compared with those obtained on thin film specimens. The spectra of complex dielectric constant, complex refractive index and conductivity are presented at temperatures of 10°K, 78°K and 298°K. The analysis of σ-spectrum in the region of chlorine doublet and the plateau near the step leads to the conclusion that the spectrum in this region consists of absorptions due to hydrogen like series of exciton. Each of the chlorine doublet standing for n =1 state exciton lines can be fitted with a suitable asymmetric Lorentzian function having a positive degree of asymmetry. The oscillator strengths of (3/2, 1/2)- and (1/2, 1/2)-components are estimated at 0.212 and 0.252 at 10°K, respectively. The exchange interaction between electron and hole of an ex...

Photo- and Thermochemical Reactions in Potassium Chloride Crystals– A Quantitative Study of the M Centre–

By experiments upon the thermal stability of the M, R and N centres in KCl crystal coloured additively, it was revealed that R 1 and R 2 centres dissociated thermally into F, M and N centres above 50°C, N centres dissociate into F and M centres above 100°C and M centres dissociated into F centres above 130°C. The relaxation time τ for the dissociation process of the M centre is expressed by 1/τ=2·10 12 ×exp (-1.31/ k T ) sec -1 for k T in ev. The corresponding experiment on the R centre was unsuccessful. With use of the above properties of photochemical products, the number of the F centre corresponded to one M centre was determined with high precision. In addition to this, the quantum yield of the M centre in the photochemical reaction with M band light was investigated as a function of temperature. Combining these two experiments with a quantitative analysis of dichroism both in the F and M bands, it is concluded that the M centre is one-electron centre, that the 2nd M band exists in the F band region, ...

The Urbach Tails and Reflection Spectra of NaCl Single Crystals

In the tail part region of the first exciton band, the absorption constant (10 -1 to 10 2 cm -1 ) was measured on zone-refined and Harshaw NaCl single crystals from 10°K to 573°K. Fundamental absorption tails of pure NaCl single crystals are represented by the modified Urbach rule, which describes the influence of zero-point lattice vibrations at low temperature. Analysing a temperature dependence of Urbach constant σ=σ 0 F , it was found that σ 0 =0.757 and the temperature of zero-point phonon is \(\omega\hbar/2{=}58.2\)°K. Reflection spectra of single crystals were measured from 2112A to 1060A in the same temperature range. The peak shift of the first reflection band is investigated as a function of temperature to clarify the mode of phonons interacting with the exciton in the main part of the band.

Anisotropic Optical Spectra of YAlO3 (YAP) Single Crystals in the Vacuum Ultraviolet Region

Optical spectra of YAlO 3 (YAP) single crystals are measured for , and // E in the region from 6.5 eV to 42 eV by use of a plane polarized synchrotron radiation, E being the electric field of light. Anisotropic spectral behaviour of the intrinsic absorption including the tail absorption is found, and a tentative interpretation of spectral features is given in terms of the energy levels of the constituent atoms of YAP. It is found that the principal factor determining the interband absorption onset position is the bond length of Y 3+ -O 2- in the compounds of Y 2 O 3 , YAP and YAG. The steepness constants σ s0 of these compounds are found to decrease in magnitude with increasing deviation from the mean value of the Y 3+ -O 2- bond lengths participated in the tail absorptions.