Symmetry-related transitions in the spectrum of nanosized Cubic Y2O3: Tb3+

Abstract

Herein the preparation and cathodoluminescence of nanoparticles of cubic Y<inf>2</inf>O<inf>3</inf>:Tb³⁺ having Tb³⁺ concentration varying between 0.1 and 10 Mol% are described. The cathodoluminescence spectra were recorded with a high resolution spectrometer, which enabled the identification of Tb³⁺ lines with C<inf>2</inf> and S<inf>6</inf> symmetry: the lines at 542.8 nm and 544.4 nm were designated as 5D4→7F5 (C2) and 5D4→7F5 (S6) respectively. The critical distance for energy transfer from Tb³⁺ ions at S6 lattice sites to Tb³⁺ ions at C<inf>2</inf> lattice sites was found to be >1.7 nm. At the greater distances which prevail at low Tb³⁺ concentration, this energy transfer virtually stops. From cathodoluminescence spectra recorded in a scanning transmission electron microscope it was concluded that this energy transfer also did not take place if the temperature was reduced below 102 K. The efficiency of the cathodoluminescence of 1% Y<inf>2</inf>O<inf>3</inf>:Tb³⁺ was 6 lm/w at a beam voltage of 15 kV. The decay time of the 5D4→7F5 (C<inf>2</inf>) transition was substantially shorter than that of the 5D4→7F5 (S6) transition at low Tb³⁺ concentrations. The decay behavior of the cathodoluminescence images in a field emission scanning electron microscope has been explained in terms of phosphor saturation.