Luminescence properties of A2ReCl6 crystals
Abstract
At temperatures below 60 K A2ReCl6(A = K, Rb, Cs) crystals emit intense, well resolved luminescence in the 13 900–12 800 cm–1 region under blue–green excitation. The emission is strongly temperature dependent and also depends somewhat on the excitation wavelength and crystal quality. It is here assigned as the vibronic structure associated with the Γ7(2T2g)→Γ8(4A2g) transition of centrosymmetric and essentially octahedral ReCl62– ions at up to nine distinct defect sites. The compounds (NR4)2ReCl6(R = CH3, C2H5) also luminesce in the same spectral region but more weakly than the alkali-metal salts. [N(n-C4H9)4]2 ReCl6 does not luminesce under these conditions. The nature of the defect sites and their excitation processes are discussed.