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 Eg of ZrP2O7 and KZr2(PO4)3 are estimated as 6.7 and 6.6 eV respectively. -- Highlights: ► ZrP2O7 and KZr2(PO4)3 crystals reveal intrinsic PL bands peaking at 295 nm ► Excitation bands of the UV emissions are related to the onsets of band-to-band transitions. ► The electronic structure calculations indicate the O–Zr CT character of the excitation bands. ► The Eg values of ZrP2O7 and KZr2(PO4)3 are estimated as 6.7 and 6.6 eV respectively