No abstract

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 work deals with the epitaxial PbSe layers grown on the KCl substrates by the method of “hot-wall” molecular epitaxy over the range of layer thicknesses of 20 - 2000 nm. Special emphasis is put on the values of elastic deformations that could be generated and frozen in epitaxial layers with the aim of influencing their energy spectra and optical properties. The maximum deformation at layers tension made up 57% of the initial mismatch between the layer and the substrate (ε = Δa/a = 0.015). In such a solid-state structure effective “negative” pressure is realized, which is justified by increase in the tangential lattice constant and the forbidden gap width. This width correlates with the tangential lattice constant (deformation) and corresponds to certain values of definite frequencies of direct electron transitions across the forbidden gap

The article deals with the peculiarities of creation of effective negative pressure and the increase in the forbidden gap width in PbSe nanolayers. The dielectric state that maybe realized under these conditions and their appropriate doping can be considered as a new resource in lead selenide nanolayers. The increasing of the tangential lattice constant with higher growth temperature and layer growth rate confirms this consideration. When determining the forbidden gap width, the optical transmission spectra were processed by a model of the Fabry-Perot interferometer, and, at high concentration of free current carriers, the absorption on them and their degeneracy were taken into consideration.