The Infra-red Emission of Indium Sesquisulphide

Indium sesquisulphide (In 2 S 3 ) has been synthesized from its constituent elements in a closed two-zone furnace system. The sulphur pressure is controlled by the zone temperatures. Both single crystals and polycrystalline specimens show infra-red emission at 90 °K with spectral maxima at 0 79 and 0.88 μm. Excitation is achieved using shorter wavelength radiation (0.5 to 0.7 μm). After excitation at low temperatures, warming in the dark produces thermoluminescence, peaks occurring at 113 °K and 126 °K. The peaks are very sharp and follow a form expected from a bimolecular trapping mechanism, the second peak at 126 °K corresponding to a trap depth of 0.35 eV. The frequency factor obtained is about 10 14 sec -1 and leads to trap cross sections of the order of 10 -12 cm 2 , which indicates the `giant' nature of such traps. The possible origin of these traps in the cation defective crystal lattice is discussed.