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Results of a complex study of electroabsorption, photoconductivity, and luminescence of two groups of cadmium thiogallate single crystals are presented. The energy positions of levels of deep centres are found. Some assumptions about the characteristics of these levels are made and the scheme for radiative electron transitions in CdGa2S4 single crystals is proposed.

Luminescence, decay, and thermal quenching under photonic excitation of CaGa2S4:Eu2+ mono and polycrystals have been measured. For excitation into the lower 5d states, thermal quenching starts above 350 K, which makes this material appropriate for use as a yellow phosphor under excitation by blue-emitting diodes. Thermoluminescence after 337.1 nm irradiation is explained by photoionization of Eu2+ ions. © 2002 The Electrochemical Society. All rights reserved.

Luminescent properties of CaGa 2 S 4 :Er polycrystals in the visible and infrared spectral ranges were investigated. The presence of two different point symmetries for Er 3ϩ centers is well established by selective and polarized photoexcitation. The Ca thiogallate compound can be considered as a promising material for optical communication purposes due to the intense Er 3ϩ infrared luminescence in the 1.55 m range.Erbium-doped materials are of great interest in the thin film integrated optoelectronic technology, due to their Er 3ϩ intra-4f infrared ͑IR͒ emission at 1.55 m, a standard telecommunication wavelength in band C ͑1530 to 1560 nm͒. Dielectric thin films of different Er-doped materials can be used to fabricate planar optical amplifiers or lasers 1-5 that can be integrated with communication systems. In wide bandgap materials, Er 3ϩ ions provide also several emissions in the visible range. The ratio of the visible and IR emission intensities depend on the host material type and erbium concentration. 6 In materials with a small phonon energy the visible luminescence predominates 7 under ultraviolet ͑photoluminescence, PL͒ and electron-beam ͑cathodoluminescence, CL͒ excitations. In oxides, 8 because of the large phonon energy, the multiphonon relaxation of the excited electrons to the lower levels give rise usually to infrared and red emissions.Owing to these considerations, using small phonon energy sulfides is a possibility for practical applications. But these materials must be stable toward hydrolysis and have a high solubility for rare-earth elements.Thiogallates of the different second group elements are convenient for all the reasons mentioned above. 9 CaGa 2 S 4 and SrGa 2 S 4 crystallize in the orthorhombic system with the space group D 2h 24 -Fddd 10 with Ca and Sr ions located in three slightly different sulfur square antiprisms ͑Wyckoff positions: 8a, 8b, and 16e͒. But it has been established that for the strontium thiogallate compound doped with Nd and codoped with Na for charge compensation, there is an ordered distribution of Na ϩ and Nd 3ϩ ions: the Nd 3ϩ ions occupy the a and b polyhedra which have no common apex. 11 Therefore, the interactions responsible for concentration quenching are considerably reduced.CaGa 2 S 4 :Er luminescence properties have been intensively investigated in the visible range up to 700 nm in the past. 9,12,13 The main task of this paper is to analyze the luminescence properties of Er in the IR range and by selective laser spectroscopy and polarization methods to index the emission lines and determine the nature of the corresponding luminescence centers. MeasurementsThis paper describes the results obtained for CaGa 2 S 4 :Er polycrystals prepared by solid-phase synthesis from stoichiometric amounts of calcium ͑CaS: 99.99͒ and gallium (Ga 2 S 3 : 99.95) sulfide powders in a sulfur vapor atmosphere at 1000°C in a vacuum pumped sealed quartz bulb. Activation by Er ͑2 atom %͒ was realized using ErF 3 ͑99.9͒ doping during the synthesis process.The photon excitation at 33...

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