The photoluminescence properties of EuGa2S4:Er polycrystals under 337.1 and 976 nm laser excitations versus temperature (78–500 K) are presented. Under 337.1 nm excitation wavelength, a wide emission band corresponding to Eu2+ ions in the visible range and emission lines of Er3+ in the visible and near infrared were observed. These emissions were also observed under 976 nm excitation wavelength with a two-photon absorption accompanied by a phonon assisted energy transfer to Eu2+ ions. According to experimental conditions, energy transfers from Eu2+ to Er3+ and from Er3+ to Eu2+ are highlighted.

The photoluminescence of barium thiogallates doped with Eu 2+ , Ce 3+ , and Eu 2+ + Ce 3+ ions is studied over a wide range of excitation levels (10 -3 -10 6 W/cm 2 ). Introduction of 3 at.% Eu and 3 at.% Ce instead of 5 at.% Eu into a BaGa 2 S 4 matrix doubles the luminescence quantum yield of the phosphor. Doped BaGa 2 S 4 exhibits a high linearity in its luminescence intensity as a function of excitation level (a constant efficiency) up to 2⋅10 4 W/cm 2 for excitation pulse durations of 8 ns, which corresponds to cw pumping at a power density of about 5⋅10 2 W/cm 2 in terms of the concentration of excited ions. It is shown that using BaGa 2 S 4 :Eu,Ce along with the "yellow" phosphor of a Nichia NS6L083 LED may increase its color rendering index from 0.64 to 0.80 with no reduction in its luminous efficiency.

The luminescent properties of undoped and doped GaSe single crystals in the region of the fundamental absorption edge have been studied by a number of authors /1 to l o / . The impurity photoluminescence (PL) in GaSe is not completely understood as compared to the near-gap luminescence /11 to 13/. Investigations of P L spectra of GaSe:Mn single crystals at 4.2 K a r e dealt with by the authors of /12/ and /13/. However, the authors of these reports have not studied excitation spectra, P L kinetics, dependences of the shapes and

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