Luminescent rare-earth ions doped Al2O3–Y2O3–SiO2 glass microspheres prepared by flame synthesis

A flame-spraying technique was applied for preparation of undoped and 1 mol% Nd- and Er-doped Al2O3–Y2O3–SiO2 (YAS) glasses with 5, 10, 15, and 20 mol% of SiO2. The glasses were prepared in the form of microspheres by melting precursor powders synthesized by the Pechini method in CH4–O2 flame, and by quenching micro-droplets of the melt by spraying them with deionized water. Prepared transparent glass microspheres were characterized by optical microscopy, SEM, XRD, DTA, UV–vis–NIR, and fluorescence spectroscopy. The undoped microspheres were amorphous, as confirmed by the X-ray powder diffraction. Addition of silica has negligible effect on glass transition temperature, and the temperature of crystallization, due to high structural similarity of all prepared glasses. UV–vis–NIR/fluorescence spectra showed typical absorption/emission/excitation bands due to the presence of optically active Nd3+ and Er3+ ions in the host glass. The Er3+ doped glasses exhibited the strongest excitation at 378 nm, which corresponds to 4I15/2→4G11/2 transition of the Er3+ ion. They exhibited strong green emission at 548 nm (4S3/2→4I15/2) and a weak green emission at 525 nm (2H11/2→4I15/2). The intensities of emission bands decreased with increasing SiO2 content. The Nd3+ doped glasses exhibit three major emission bands at 905, 1067 and 1340 nm, corresponding to the 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions, respectively, of the Nd3+ activator. The emission intensities were not influenced by the content of SiO2. The wavelength of emitted light was not influenced by the structure of glass.