Structure and luminescence of (Ca,Sr)2SiS4 : Eu2+ phosphors

Sr2SiS4 : Eu2+, Ca2SiS4 : Eu2+ and the solid solution of both, europium-doped (Ca,Sr)(2)SiS4, were investigated as UV-VIS excitable green to red powder phosphors. Sr2SiS4 : Eu2+ shows two emission bands, peaking at 480 and 550 nm. By changing the ratio between Ca2+ and Sr2+, the photoluminescent emission spectrum can be tuned. Using x-ray diffraction, the phase composition and lattice parameters of the thiosilicate compounds were determined. The material forms a single, monoclinic Sr2SiS4-like phase up to 40% substitution of Sr2+ by Ca2+. From 50% to 90% of substitution by Ca2+, phase separation was observed, leading to more complex emission spectra. These spectra were studied in detail using photoluminescence spectroscopy, cathodoluminescence microscopy and temperature dependent optical measurements. The thermal quenching temperature decreases from 470 K in Ca2SiS4 : Eu2+ to 380 K in Sr2SiS4 : Eu2+ upon increasing substitution of Ca2+ by Sr2+. The possibilities of these materials as wavelength converters for white light emitting diodes were evaluated.