Charles J. Delbecq

Some Optical Properties of Potassium Iodide‐Thallium Phosphors

The absorption spectra of potassium iodide‐thallium phosphors have been studied at both liquid nitrogen and liquid helium temperatures. Eight absorption bands have been observed which are due to the presence of thallium. The maximum absorption coefficients of four of these bands appear to vary linearly, while the other four appear to vary with the square of the thallium concentration. The origin of these bands is discussed in terms of an extension of the model proposed by Seitz.

A New Type of Short Wavelength Absorption Band in Alkali Halides Containing Color Centers

Photo‐chemically and additively colored potassium iodide crystals exhibit absorption bands in the ultraviolet which do not have the characteristic properties of V‐bands. An interpretation of the origin of these bands is proposed.

A study of M center formation in additively colored KCl

Additively colored crystals of KCl were cooled rapidly from a high temperature and then exposed to light absorbed by the F band. The rate of growth of the M band was initially low and increased markedly during the first part of the irradiation giving rise to what is called a “delay period” in the M center formation. During this delay period it was observed that 1. the quantum efficiency of F center fluorescence decreases by a factor of 3 or 4, and 2. the ability to convert F centers to F′ centers is reduced by about a factor of 3. These effects are interpreted as arising because of an appreciable decrease in the average nearest neighbor F center separation during this period.Results are also presented concerning the kinetics of M center formation, oscillator strengths of the M center transitions, the degree of polarization of the M center fluorescence, and the transfer of energy from an excited F center to an M center.

Absorption Bands and Lines in Irradiated LiF

The paper deals with a number of phenomena observed in lithium fluoride after formation of color centers by exposure to x‐rays, Van de Graaff electrons, or neutrons and not observed in other alkali halides under similar conditions. The most important of these phenomena are: (1) The appearance of a new band at 222 mμ, when the crystal is bleached with light of wavelength 254 mμ absorbed in the F band, and the inverse effect by subsequent irradiation with light of shorter wavelengths. (2) The production of F centers in a crystal heated to temperatures up to at least 450°C. The higher the temperature at which the F centers were produced, the greater is the intensity of the band at 222 mμ obtained by subsequent optical bleaching of the F band at room temperature. (3) The appearance of fine structure in a relatively weak band with peak at 380 mμ and of a very weak line at 523 mμ when the spectrum is recorded at the temperature of liquid nitrogen. (4) The very strong increase in the intensity of the band at 380...

Photon‐Induced Diffusion in Thin Films and Single Crystals of Potassium Iodide

Thin films of potassium iodide have been prepared at both room and liquid nitrogen temperatures. Absorption spectra are presented which show that films deposited at liquid nitrogen temperature are quite disordered, but after warming to room temperature are very similar to those films deposited at room temperature. Evidence is given which shows that in thin films and also in single crystals of potassium iodide diffusion is promoted by the absorption of light. It is proposed that diffusion is caused by point thermal spikes at the absorbing centers.

The 〈110〉 oriented FCl− molecule–ion in KFa)

The heteronuclear diatomic molecule–ion FC1− with its molecular axis oriented along a crystal face diagonal, i.e., FC1− 〈110〉, has been produced by ionizing radiation in single crystal KF doped with PbCl2 and KC1. Evidence to support this species identification as well as its orientation relative to the lattice is obtained from anisotropic optical absorption spectral measurements as well as from electron spin resonance (ESR) absorption spectra. Optical absorption spectral data, estimates of the molecular reorientation temperature, as well as ESR absorption spectral parameters are given for the FCl− 〈110〉. A qualitative explanation of the differences of the optical and ESR parameters of FCl− 〈111〉 and FCl− 〈110〉 is discussed.