Abstract
Herein the photoluminescence spectra of nanosized cubic Y2O3:Tb3+ having Tb3+ concentrations varying between 0.1 and 10 Mol% are described. Low temperature cathodoluminescence spectra from these materials recorded in a scanning transmission electron microscope are presented and discussed. By studying the photoluminescence-spectra recorded at room temperature and focused on the 5D4→7F5 (C2) and 5D4→7F5 (C3i) transitions, at 542.8 and 544.4 nm respectively, it was found that the critical distance for energy transfer from Tb3+ ions at C3i lattice sites to Tb3+ ions at C2 lattice sites was 1.7 nm; at distances >1.7 nm, which prevail at low Tb3+ concentration, this energy transfer virtually stops. The gradual change of the excitation spectra upon increasing the Tb3+ concentration is also explained in terms of energy transfer from Tb3+ at C3i sites to Tb3+ at C2 sites. Cathodoluminescence spectra recorded at low temperatures with the scanning transmission electron microscope provided additional evidence for this radiationless energy transfer.
Highlights
We identified a few peaks in the CL spectra that are related to Tb3+ at C3i sites in cubic Y2O3
This symmetry-related assignment is based on the analyses of the CL spectra reported in Part 1: the peak at 542.5 nm was identified as C2 and the peak at 544.2 nm as C3i
We have presented preliminary measurements of the CL spectra of 3% Y2O3:Tb3+, which have been recorded with the Vulcan CL detector of the TEM at various temperatures in Part 1
Summary
Concentration quenching was identified as an important issue in several publications on the PL spectrum of Y2O3:Tb3+ It was discussed by Najafov et al.[4] and measured by Muenchausen et al.;[5] these latter authors found that the PL efficiency peaked at 0.5 Mol% in bulk Y2O3:Tb3+ material, whereas for their nano-material with particle size of 35 nm it peaked at 1.5% Tb3+. A third possibility, direct Tb3+ excitation through a 4f8→4f8 transition, was mentioned by Som et al.[13] We shall adopt here the assignment of Kano:[7] the excitation band between 260 nm and 340 nm is due to 4f8→4f75d1 transitions, since the CT band of Y2O3:Tb3+ is positioned at 64000 cm−1 (156 nm) in the VUV These assignments were confirmed by Dorenbos, see for instance Ref. 14 and publications cited in this recent paper.
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