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 XF_2, 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.