The Concentration Quenching of Photoluminescence and the Quantum Yield in (Y1–xPrx)2O2Se Solid Solutions

(Y1–xPrx)2O2Se solid solutions with х = 0.004, 0.008, 0.010, 0.012, and 0.020 have been prepared from oxides by ampule synthesis. We have measured their excitation spectra at λem = 514 nm and their photoluminescence and quantum yield spectra at λex = 463 nm (T = 300 K). Comparing their emission intensities at wavelengths of 514 (3P0 → 3H4 transition) and 670 nm (3P0 → 3F2 transition), we have determined the optimal dopant concentration (x = 0.01), at which the quantum yield has a maximum, reaching 3%.