Photoluminescence Kinetics of CaGa2S4:Nd,Yb Crystals at Room Temperature

The photoluminescence (PL) spectra, PL excitation spectra (PLES), and PL kinetics of micropowders of CaGa₂S₄:3%Nd,5%Yb and CaGa₂S₄:3%Nd compounds at room temperature were studied in a broad range of optical excitation levels. In the PL spectra and PLES, the transition bands of the Nd³⁺ ions in the wavelength range 300–1500 nm were identified. Doping of the CaGa₂S₄:3%Nd crystals with ytterbium ions leads to the appearance of an intense violet-green band with maximum at 488 nm in the PLES. When excited within this band, the PL intensities in the IR bands of neodymium are increased by two orders of magnitude but when excited outside this band, the enhancement is only by one order of magnitude compared to the analogous PL intensities of the undoped crystal. Experimental decay of PL is observed upon excitation to the Nd absorption bands. An initial rise in photoluminescence is observed upon excitation to the broad band arising upon doping of CaGa₂S₄:Nd with ytterbium followed by exponential decay. The major features of the PL decay kinetics in CaGa₂S₄:3%Nd,5%Yb were interpreted in the framework of a mathematical model for nonradiative energy transfer (Förster Resonance Energy Transfer, FRET).