Radiative to Non-Radiative Processes for Luminescence of Eu²⁺ Ion in SrF₂ -BaF₂ Mixed Crystals

Abstract

The optical properties of blue and yellow luminescence have been investigated for Eu ²⁺ (4f ⁷ ) ions doped into mixed crystals or solid solutions Sr _1-x Ba _x F ₂ (0≤ x ≤1.0), focusing on the thermal relaxation mechanism. The intense blue band observed in Sr-rich crystals exchanges for a yellow one in Ba-rich crystals below 100 K.For varying the mixture ratio, the two bands conserve persistently each quantity of luminescence peak, intensity, half-linewidth, and lifetime.First measurements of the precise lifetime and the thermal activation energy were carried out against the variation of mixture ratio as well as temperature. For the yellow luminescence, it was found that there was a large difference in the decreasing rates between the spectral intensity and the lifetime.A mechanism of energy transfer from blue to yellow luminescence is discussed byapplying the configuration coordinate diagrams.