Electronic structures and origin of intrinsic luminescence in Bi-containing oxide crystals BiPO4BiPO_4, K3Bi5(PO4)6K_3Bi_5(PO_4)_6, K2Bi(PO4)(MoO4)K_2Bi(PO_4)(MoO_4), K2Bi(PO4)(WO4)K_2Bi(PO_4)(WO_4) and K5Bi(MoO4)4K_5Bi(MoO_4)_4

The origin of intrinsic photoluminescence (PL) in the set of Bi-containing phosphate, molybdate and tungstate crystals is analyzed in complex experimental and computational studies. The PL properties of polycrystalline powder samples of BiPO4, K3Bi5(PO4)6, K2Bi(PO4)(MoO4), K2Bi(PO4)(WO4) and K5Bi(MoO4)4 crystals synthesized by spontaneous crystallization method are studied under excitations in the VUV and UV region of photon energies (3.5–14 eV) at T = 8–300 K. The electronic band structures of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. The values of band gaps Eg of studied compounds are estimated from diffuse reflectance and PL excitation spectra. Calculations indicate that all studied crystals except K5Bi(MoO4)4 are indirect-gap materials. It is found that the Bi 6s and Bi 6p states contribute respectively at the tops of the Valence bands and the bottoms of the Conduction bands of all studied compounds. Each studied compound reveals several (at least two) PL emission components which undergo complete quenching below room temperature. Under nitrogen laser excitation with λex = 337.1 nm, all studied crystals reveal single-exponential decay of PL signal with decay constants τ in 3–35 μs range. It is assumed that the high-energy PL components of BiPO4, K3Bi5(PO4)6 and K2Bi(PO4)(MoO4) (peaking in the blue and violet regions) originate from 3P1 → 1S0 radiative transitions in Bi3+ ions. The red PL components of K2Bi(PO4)(MoO4) and K5Bi(MoO4)4 have the MoO42−-related origin. The red PL component of K2Bi(PO4)(WO4) presumably originates from the molybdenum impurities which form MoO42− emission centers in the phosphate–tungstate host