Temperature effects on luminescence properties of Cr ³⁺ ions in alkali gallium silicate nanostructured media

We have investigated the optical properties of Cr3+ ions in an alkali gallium silicate glass system and in two glass-based nanocomposites with nucleated Β- Ga2 O3 nanocrystals. The nucleation and growth of the nanocrystalline phase in the host glass matrix were monitored by Raman scattering spectroscopy and angle-dispersive x-ray diffraction. A broadband luminescence, associated with the T24 - A24 transition from the weak crystal field of octahedral Cr3+ sites, dominated the emission of the precursor as-quenched glass. The luminescence spectra of the synthesized glass-ceramic nanocomposites revealed a crystal-like E2 - A24 strong emission and indicated that the major fraction of Cr3+ ions was located within the nanocrystalline environment. The variable-temperature studies of the nanocomposites demonstrated that the fluorescence of Cr3+ ions can be transformed from sharp R lines of the E2 - A24 transition to a combination of R lines and of the broad band of the T24 - A24 transition. We propose a simple distribution model where the major part of Cr3+ ions is located in the nanocrystalline phase of the glass-ceramic composites in the octahedral environment, substituting the gallium atoms in the Β- Ga2 O3 crystal structure. The developed nanocrystalline glass-ceramics are a promising class of Cr3+ -doped oxide glass-based optically active composite materials.