EPR and optical studies of Cr-doped PbWO4 single crystals

Electron paramagnetic resonance (EPR) studies were performed on Cr ions in PbWO4 crystals using an X-band spectrometer. With the help of Fourier-transform infrared (FTIR) and thermoluminescence (TSL) data, it was proposed that Cr3+ impurities enter PbWO4 lattice in the Pb-site and result in large relaxation of crystal lattice, which was illustrated by the significant distortion of WO4 tetrahedron and the rapid decrease of blue luminescence band. Further, for heavily doped samples some new EPR signals, which did not appear in the lightly doped sample, were detected. The new EPR lines were ascribed to the exchange-coupled effect of Cr3+-ion pairs. Luminescence spectra provide support to the idea about defect clusters. The presence of Cr3+-ion pairs or Cr3+-ion associations in heavily doped PWO is the reason for the luminescence quench of PWO host and Cr3+ ion.