Electronic structure and optical properties of ABP2O7ABP2O7 double phosphates

Luminescence and luminescence excitation under VUV radiation of ABP2O7ABP2O7 (A=NaA=Na, K, Cs; B=AlB=Al, In) double phosphates are studied. Two emission bands peaking near 330 and 420 nm are common for investigated ABP2O7ABP2O7 crystals. The band structure and partial densities of electronic states of perfect KAlP2O7KAlP2O7, LiInP2O7LiInP2O7 and NaTiP2O7NaTiP2O7 crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. It is found that the structures of the conduction bands of ABP2O7ABP2O7 crystals, which have different B cations, are appreciably different. Experimental results are compared with results of calculations of the electronic structure. Assumptions concerning the origin of luminescence in double phosphates are made.