Abstract
The glasses of the composition 37PbO–8Al2O3/ Sc2O3/ Y2O3−54SiO2: 1Ho2O3 (Holimium series), 37PbO–8Al2O3/ Sc2O3/ Y2O3−54SiO2: 1Er2O3 (Erbium series) and 37PbO–8Al2O3/ Sc2O3/ Y2O3−54SiO2: 0.5Ho2O3+0.5 Er2O3 (codoped series) have been synthesized. Optical absorption and fluorescence spectra in the spectral range 300-2000 nm were studied at ambient temperature. The Judd-Ofelt theory could successfully be applied to characterize the optical absorption and emission spectra of these ions. The comparison of branching ratios β values of blue, green and red emissions for both the series of the glasses showed the largest values for glass mixed with Y2O3. A noticeable enhancement in the intensities of blue, green and red emission levels has been observed due to co-doping and is found to be the highest for the glasses mixed with Y2O3. The reasons for this enhancement have been analyzed in the light of varying environment of rare earth ions due to different sesquioxides in the glass network. The Al3+, Sc3+ and Y3+ are expected to be coordinated by three SiO4 tetrahedral ligands. Two of the oxygen ions associated with each tetrahedron is assumed to be non-bridging ions forming ionic bonds with these trivalent ions. However in case of Y3+ ions silicate tetrahedra must be moved more outward since the ionic radius of this ion is more when compared with that of Al3+ and Sc3+ ions. In view of this, although three ions are linked in triangle with SiO4 structural units, the octahedra of yttrium ion is more distorted when compared with that of the other two ions
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