Optical properties of Pb2MoO5 and Pb2WO5 single crystals as materials for practical applications

The low-gradient Czochralski method was used to obtain lanarkite type Pb2MoO5 and Pb2WO5 crystals. Photoluminescence properties under UV excitation were studied, such as temperature dependences of decay time and excitation and emission spectra. The Pb2MoO5 crystals demonstrate intensive emission spectra in green range under 350 nm excitation and yellow-red range under 325 nm excitation. Pb2WO5 crystals exhibit green-blue luminescence under 400 nm excitation and green-yellow luminescence under 340 nm excitation. Photoluminescence spectra for investigated crystals show a short wavelength shoulder in violet spectral region near 400-420 nm. These violet component of photoluminescence for lead crystals are attribute to the transitions triplet states T-1(1,2) of MoO4-2 and WO4-2 groups, respectively. The band gap of Pb2MoO5 and Pb2WO5 crystals were estimated from UV absorption spectrum and are equal to about 3.45 eV. Correlated color temperatures and color purity for both crystals at different excitations were calculated and the conclusion was made about the possibility of using such crystals in warm white light emitted diodes and other solid-state lighting applications. Color chromaticity coordinates are shown on CIE1931. Temperature dependence of decay time constant allowed us to calculate sensitivity for non-contact thermometry applications.