Yoichi Uchida

On the V-centers in Alkali Iodide Crystals

The properties of V-center were investigated in the alkali iodide crystals (KI and NaI) containing excess iodine, In KI, the absorption spectrum was similar to that obtained by Mollwo, but for details, there were some difference. It was pointed out that the V-band in KI can be understood as superposition of three bell-shaped bands I , II , and III . Of these, both band I and II can be safely assigned to V 2 -band. As for band III , however, explanation is not possible at present though it seems to have fairly close relation to the other two bands. Some proposals were made in regard to the mechanism of the coloring with the pointed electrode and the explanation of the doublet structure of V 2 -band in KI.

Thallous Ion Centers in Potassium Iodide-Thallium Crystals

Absorption, excitation, and emission spectra of KI-Tl crystals have been investigated over the temperature range from 10°K to 300°K. The C band has a temperature sensitive triplet structure and the A band has a temperature sensitive asymmetry. The absorption intensities of the paired thallous ion bands are independent of temperature. Excitation in any band of the paired thallous ion center produces the same single 412 mµ emission band at 10°K. The luminescent processes in the paired thallous ion center are discussed basing on the model of the pseudomolecule composed of two thallous ions. Moreover, the experimental results on the paired thallous ion center in KI-Tl crystals are compared with the previous results on the center in NaI-Tl crystals.

Optical Studies on Thallium-activated Alkali-iodide Crystals

Absorption and emission spectra of KI–Tl and NaI–Tl phosphors have been investigated at both room and liquid air temperatures. In order to perform optical measurements on NaI-Tl, special caution was given to prevent the crystal surface from being clouded by moisture. In the absorption spectra of NaI–Tl, new bands due to the presence of thallium were found. Their maximum absorption coefficients seemed to vary with the square of the thallium concentrations. The similar fact has already been found by Yuster and Delbecq in their investigation on KI–Tl. In emission, both KI and NaI crystals containing high concentrations of thallium showed a subsidiary band overlapping the short wavelength tail of the hitherto observed main band. The relations between these absorption and emission bands were investigated and discussions were given in terms of an extended model proposed by Seitz.

On the Oscillator Strength of V 2 Centers in Potassium Iodide Crystals

By measuring the absorption of dilute aqueous solutions of KI with various known amounts of pure iodine added, the present writers have observed that the absorption coefficient at a wavelength of about 350 mμ is nearly proportional to the amount of iodine in the solution. Making use of this fact, the amount of excess iodine in additively V-colored KI crystal has been obtained. Taking into account that two iodine atoms are associated with a V2 center, the oscillator strength of the absorption band at 365 mμ has been estimated to be 1.10±0.16 by the Smakula formula.

Extreme Ultraviolet Spectroscopic Optics in Japan

A brief review is presented of the work recently carried out in Japan in the field of the extreme ultraviolet spectroscopic optics. It also includes names of people and organizations active in the research.

Cathodeluminescenee of Beryllium Oxide and its Related Compound

The cathodoluminescence spectra of BeO, CaO, and MgO are measured at 90 and 320 deg K. In each of these compounds, two series of oxygen-sensitive emission bands are found that are enhanced at the low temperature. (T.F.H.)

Optical Properties of Sodium Iodide-Thallium Crystals

The optical absorption and luminescence of sodium iodide crystals containing thallium at various concentrations have been studied. It is found that a pair of thallous ions replacing two adjacent sodium ions in the crystal has absorption bands at 305 and 310 mµ, the former exciting the 325 mµ emission band and the latter the 425 mµ emission band, all bands being measured at 77°K. Study of the polarized luminescence from these bands confirms the above-mentioned model for the double thallous ions and suggests the nature of its electronic structure.

Extreme Ultraviolet Emission from Beryllium Oxide

Spectra of cathodoluminescence and luminescence excited in a discharge tube were observed on BeO, MgO, and CaO samples prepared by heat-treatments in N2 or O2 atmosphere and the emission bands of these samples in the ultraviolet and vacuum ultraviolet regions were examined. From these experiments it has been found that BeO samples obtained by heating in O2 atmosphere, when excited by electron beams at liquid air temperature, emits strong radiation extending from 3 to 7 ev.