Luminescence: Photoluminescence (PL), upconversion (UC), and photoluminescence excitation (PLE) spectra of samples at room temperature were recorded using an FLS1000 photoluminescence spectrometer (Edinburgh Instruments) equipped with a 980 nm laser (2 W of optical power) and a Xelamp as excitation sources. The luminescence decay curves of UC phosphors were measured in the same instrument at room temperature under excitation by the 980 nm laser in pulsed mode. The dependence of the peak intensity of UC luminescence was recorded by varying the pump power of the 980 nm laser using an iris filter. All samples tested were placed in a fused silica sample holder. The diskshaped samples used for PL and UC measurements were obtained from crystallized beads by polishing two parallel faces.