ESR AND OPTICAL SPECTROSCOPY OF COPPER-DOPED PLZT ELECTROOPTIC CERAMICS

Nominally pure and Cu-doped (0.01, 0.1, and 1 wt% of copper oxide) PLZ T 8/65/35 ceramics were investigated with regard to their ESR and opti cal spectra (absorption and luminescence). ESR investigations were per formed at 4.2 K less than or equal to T less than or equal to 300 K in the X and K bands both before and after annealing the samples in oxyg en and hydrogen atmospheres. The observed spectra were shown to be a s uperposition of Cu2+ spectra in axial and cubic crystal fields. Cu2+ s ubstitutes for Ti4+ and the excess charge can be compensated by La3+ o n a nearest-neighbor site, thus creating axial symmetry. The centers o f cubic symmetry are those where the charge is compensated in distant spheres. In contrast to pure PLZT, PLZT:Cu exhibits a new luminescence band peaking at 1.18 eV. This emission is ascribed to the T-2(2)(D) - -> E-2(D) transition of Cu2+(3d(9)) which can be excited either in the resonant 1.87 eV band or via charge-transfer excitation bands at 2.40 , 2.57, and 3.03 eV. The absorption band at 1.45 eV is assumed to be t hat of Cu+ ions. Annealing in hydrogen and in oxygen atmospheres cause d decrease and restoration, respectively, of the ESR and luminescence intensities as a consequence of Cu2+ conversion into Cu1+ and vice ver sa.