Luminescence spectroscopy and electronic structure of ZrP2O7 and KZr2(PO4)3 crystals

The photoluminescence (PL) of ZrP₂O₇ and KZr₂(PO₄)₃ phosphate crystalline micro-powders grown by spontaneous crystallization method is studied under vacuum ultra-violet (VUV) synchrotron radiation excitations (4–20 eV region of excitation photon energies) in 8–300 K temperature region. The electronic structures (partial densities of states) and optical absorbance spectra of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. Both phosphate crystals reveal PL emission band in the UV spectral region peaking near 300 and 295 nm for ZrP₂O₇ and KZr₂(PO₄)₃ respectively. The spectral profile of the band weakly depends on temperature. The excitation spectra of the UV emission in each crystal contain intensive excitation band peaking at 189 and 182 nm for ZrP₂O₇ and KZr₂(PO₄)₃ respectively. The excitation band of the UV emission is related to band-to-band electronic transitions with charge transfer from O 2p to Zr 4d states. The energy band gaps E_g of ZrP₂O₇ and KZr₂(PO₄)₃ are estimated as 6.7 and 6.6 eV respectively.