Photoluminescence of Ca x Ba1-x Ga2S4 Solid Solutions Activated by Eu2+ Ions

We have studied the photoluminescence (PL) of Ca (x) Ba1-x Ga2S4 solid solutions (x = 0.1, 0.2, 0.3, 0.4, and 0.5) activated by ions of the rare-earth element Eu2+ in the temperature range 10-300 K, due to 4f (6)5d -> 4f (7) transitions in the Eu2+ ions. The photoluminescence spectra of Ca (x) Ba1-x Ga2S4:Eu are located in the blue-green - green regions, and their maxima are shifted from 506 nm for x = 0.1 to 531 nm for x = 0.5. We show that the long-wavelength shift as Ca content increases is due to the increasing crystal field, in the presence of which the 5d orbitals of the europium ions are split and consequently the energy of the recombination transitions decreases. We observed high temperature stability of the position of the photoluminescence spectra and the integrated intensity (decreasing by 13% for all x) in the temperature range 10-300 K. We have established that an increase in the Ca content in Ca (x) Ba1-x Ga2S4:Eu leads to a decrease in the thermal shift of the photoluminescence, and for x = 0.5 there is no shift.