Abstract

Previous work has revealed the existence of high field site (HFS) Cr³⁺ ions in the mullite glass ceramics which relax through R-line emission from the excited ²E state. Recent studies of the anomalous spectral behavior of this material have suggested the existence of CR³⁺ ions at disordered low field sites (LFS) which emit broadband ⁴T₂ emission at longer wavelengths. In this paper we report the results of excitation spectra monitored at the R-line or broadband ⁴T₂ emission wavelengths which have allowed us to determine the site distribution. These measurements show that the maxima of the HFS ⁴T₁ and ⁴T₂ absorption bands lie ~1000 cm⁻¹ higher in energy and have a bandwidth ~1500 cm⁻¹ narrower than the overall absorption bands of the entire site distribution. From these data we conclude that ~10% of the ions are still in LFS in the mullite glass ceramic sample after heat treatment; radiative energy transfer exists from HFS to LFS ions resulting from the absorption of HFS R-line emission of LFS ions; the Dq value of the HFS ions increases with the degree of heat treatment. Lifetime measurements reveal a site dependence of the luminescence decay. The lifetime of the HFS R-line emission varies from 6.5 to 1.5 ms as the excitation wavelength is scanned from 532 to 670 nm, and the lifetime of the LFS ⁴T₂ emission varies from 280 to 50 μs as the excitation wavelength is scanned from 563 to 743 nm.

© 1989 Optical Society of America