Temperature and pressure dependence of the luminescence of Eu2+-doped fluoride crystals BaxSr1-xF2 (x = 0, 0.3, 0.5 and 1): experiment and model

This paper summarizes experimental evidence of anomalous luminescence in Eu2+-doped fluoride crystals BaxSr1-xF2 (x = 0, 0.3, 0.5 and 1). Luminescence, luminescence excitation spectra and luminescence kinetics obtained at ambient and high hydrostatic pressure at various temperatures are discussed. Hydrostatic pressure was shown to cause a redshift of normal 4f65d1(e)→4f7 emission and anomalous luminescence. The experimental data shows the existence of temperature- and pressure-induced spectral transformations where the anomalous luminescence is replaced by normal emission of Eu2+ centers. We present a model that predicts a strong electron-lattice coupling of the trapped excitons as well as the pressure effect of the spectral transformation from anomalous to normal emission.