Photoinduced Phenomena in Sulphur Crystals and Films

Abstract

The irradiation of sulphur crystals and films with ułtraviolet light induces the change of transmission in the visible part of spectra. It was found that these phenomena exist onły at low temperatures (4.2-50 K). The behaviour of optical transparency as a function of time after switching the rumination off was investigated. These dependences are essentially different for the films and crystals. In order to understand the origin of these phenomena the structural investigation was conducted. Very unusual behaviour of darkening kinetics was obtained.PACS numbers: 72.40.+w, 71.55. Gs, 78.50.Ge In the recent years the interest in nonsilver photographic compounds has grown rapidly due to the high expense of silver. But on today no compounds have been found which would posess the high contrast in the low temperature range.Experimental investigations of the photoinduced properties of phosphous and arsenicum crystals have also been reported [1][2][3]. The additional absorption under the ultraviolet light in crystal P and As is caused by the shift of energy gap. The analogous measurements on the sulphur crystals were conducted by authors in [4,5] and in [6] with the use of X-rays. Despite the effort, very little is known about the mechanism of the photoinduced changes in the nonsilver halides [7][8][9][10].In this report we present an experimental investigation of the photoinduced changes caused by UV-irradiation in sulphur crystals and films. The crystals belong to the space group D. The samples were prepared from natural minerals of different quality. The quality was checked by the number of dislocations. The size of crystal surface was 12 x 12 mm2 and thickness near 5 mm. The films were evaporated on the quartz surfaces in vacuum near 10 -7 torr. The samples were mounted in the helium cryostat made in the Institute of Ukrainian Physics. They were irradiated using focused UV-light with λ ≈ 331 nm. The transmission and reflection spectra of samples were recorded using the Specord-M40 spectrophotometer. The photostuctural changes and concentration of dislocations were registered using an X-ray diffractometer.(405)

Spectral and conductivity features of novel ternary Tl1–xIn1–xSnxS2 crystals

“…All investigated crystals, regardless of х , are high‐resistant materials with p ‐type conductivity according to the sign of thermo‐EMF coefficient. The hole‐originated conductivity for the Tl 1–x In 1–x Sn x S 2 crystals may be caused by the acceptor origin of the stoichiometric cation vacancies with energy levels situated in the lower half of the band gap which is common for various complex chalcogenide semiconductors . The invariability of the conductivity type with х , accompanied by the heterovalent substitution of Sn for In (with the formation of donor centers), indicates that the concentration of the doping atoms Sn is smaller with respect to the concentration of the stoichiometric vacancies as well as other structural defects.…”

Band Structure and Charge Density Distribution of Cubic Face‐Centred TlI Single Crystals

“…All previous calculations (known to the author) on the band structure of thallous halides are performed applying the Slater approximation (u = 1) for the exchange-correlation potential. Therefore, the calculations possess only empirical character and the e(r) distribution (and E(k) dispersion as well) is approximate [17]. The results for T1I single crystals [8] (space group D;:) demonstrate the restricted validity of such an approach for this compound.…”

“…In [17] analytical expressions for the integrals (13), (14) were used. The lattice parameter of TI1 (NaCl-type) crystals is: a = 0.649 nm.…”

Band Structure and Nonlinear Optical Susceptibilities of Proustite (Ag3AsS3)

“…The calculations that have been done are either very old non-self-consistent calculations [5], or they were done without taking into account the experimental data [6]. In this work we report a tight-binding calculation of Ag,AsS, band structure corrected by experimental results on the polarized optical frequencies in visible and infrared spectral region as the scale factor.…”

“…Our previous investigations using the experimental methods of modulated spectroscopy [6] have revealed the absence of exciton effects. This can be explained by the great number of screening carriers.…”