On the synthesis, phase optimisation and luminescence of some rare earth pyrosilicates

This work concerns the synthesis, effect of fluxes on the formation of single phase materials, and spectroscopic characterization of rare earth pyrosilicates according to Ln₂Si₂O₇ (with Ln = La, Lu, Y). It turned out that by the support of LiF as a flux it is possible to obtain a single phase of the polymorph Lu₂Si₂O₇, La₂Si₂O₇, and Y_1,9La_0,1Si₂O₇ compositions. Tauc-plots of the VUV reflection spectra of these compounds were used to derive the optical band gaps, which are in the range between 6.2 and 7.1 eV. The single phase samples show strong photoluminescence in the UV and visible range upon excitation by VUV radiation or by electron bombardment. PL spectra have been measured by 160 nm excitation and cathode luminescence (CL) spectra have been recorded at electron beam energies between 2 and 20 keV, respectively. All measurements reveal that the pyrosilicates show strong defect luminescence, whereby the observed broad emission bands are assigned to different defect types.