Luminescent spectroscopy and structure of centers of the impurity Eu ions in lead tungstate crystals

Spectral-luminescent properties of the lead tungstate crystals doped with the Eu³⁺ ions were investigated in a wide temperature range at different excitation and registration wavelengths. The spectra consist of both weak wide nonstructural bands of the matrix emission and narrow spectral lines caused by inner f-f electron transitions in the impurity Eu³⁺ ions. The analysis and interpretation of spectral lines observed in excitation and luminescence spectra have shown formation of at least two different types of luminescent centers on the basis of the Eu³⁺ ions in the PbWO₄ crystals. These two types of centers are considered to be caused by arrangement of the impurity Eu³⁺ ions in Pb sites as well as in W sites of host matrix. For both types of centers values of S² scalar crystal field strength, and crystal field parameters were estimated and local site symmetries were found.