Luminescence spectroscopy and electronic structure of the PbMoO4 and Pb2MoO5 single crystals

• Pb2MoO5 single crystals reveal intensive PL band peaking at ∼600 nm.
• Pb2MoO5 is an indirect-gap dielectric crystal.
• The p states of oxygen atoms belonging to Pb–O chains form the TVB of Pb2MoO5.
• Main excitation band of the violet PL component of PbMoO4 peaks at 6.2 eV.
• Low-energy peaks in reflectivity of PbMoO4 are formed by band-to-band transitions.

Intrinsic photoluminescence (PL) and electronic structure of Pb2MoO5 single crystal are first described and compared with corresponding properties of PbMoO4 crystal. The PL properties of PbMoO4 and Pb2MoO5 crystals grown by Czochralski method are studied under the VUV synchrotron radiation excitations (3.7–14 eV region of excitation photon energies) at T = 8 K. The electronic band structures of perfect PbMoO4 and Pb2MoO5 are calculated by the Full-Potential Linear Augmented Plane Wave method. The Pb2MoO5 crystals reveal intensive PL band in the yellow–red spectral region peaking at ∼600 nm. All studied PbMoO4 samples reveal intensive PL band in the green spectral region and this band is accompanied by additional fast-decaying (τ ≈ 3.5 ns) component in the violet when the samples are grown with 30° orientation of seed with respect to the c axis. The excitation spectra of the violet component of PbMoO4 reveal complex excitation band with main peak at 6.2 eV. It is assumed that the violet PL component of PbMoO4 is generated by intra-center excitations from the ground to singlet excited states 1A1–1T1,2 of the MoO42− molybdate groups located near point defects in subsurface layer of the crystal. Strong anisotropy of reflectivity spectra of PbMoO4 below 6 eV is a consequence of peculiarities of the electronic structure of the crystal and reflectivity bands at ∼3.6 and ∼4.3 eV are formed by band-to-band electronic transitions.