Impurity-trapped excitons: Experimental evidence and theoretical concept

The paper summarizes experimental evidence of anomalous luminescence in RE-doped dielectric materials. Special attention is paid to Pr3+-doped LiNbO3 and LiTaO3, and Eu2+-doped XF2, where X = Ba, Sr. Luminescence, luminescence excitation spectra and luminescence kinetics results are discussed obtained at ambient and high hydrostatic pressure at various temperatures. Hydrostatic pressure has been shown to cause a red shift of anomalous luminescence. The experimental data show the existence of temperature- and pressure-induced spectral transformation where anomalous luminescence is replaced with normal d–f emission in Eu2+ centers. The model predicts strong electron-lattice coupling of bound excitons and relaxation in the system’s excited states, as well as the pressure effect of spectral transformation from anomalous to normal emission.