Abstract
Herein the preparation and cathodoluminescence of nanoparticles of cubic Y2O3: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 C2 and S6 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 C2 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% Y2O3:Tb3+ was 6 lm/w at a beam voltage of 15 kV. The decay time of the 5D4→7F5 (C2) 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.
Highlights
In the present report we describe a study on the cathodoluminescence of nanosized Y2O3:Tb3+ particles using the same methods as developed for analyzing the spectra of Y2O3:Eu3+
It has been well established that Y2O3 doped with various concentrations of Tb3+ and annealed at temperatures above 900◦C has the cubic structure of the mineral bixbyite;[4,5,6,7,8,9,10] the cell constant of the unit cell, 1.060 nm, does not change upon doping.[6]
It can be seen that the S6 sites have inversion symmetry, whereas the C2 sites exhibit a “small deviation” from the inversion symmetry according to Blasse and Grabmaier.[3]
Summary
We have published a study on the cathodoluminescence (CL) of nanosized Y2O3:Eu3+ particles.[1] The methods described in that report enabled a detailed analysis of the symmetry-related spectral transitions in the CL spectrum of Y2O3:Eu3+. Sotiriou et al.[4] described the effect of the lattice on the PL efficiency They found that monoclinic Y2O3:Tb3+ has a higher efficiency than the cubic phase, which needs a higher annealing temperature. This brief review of recent work on the luminescence of nanosized Y2O3:Tb3+ is in no way exhaustive; it does illustrate the widespread interest in this material
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