Influence of some sesquioxides on up conversion in Ho3+−Er3+ co-doped PbO−SiO2 glass system

Abstract The glasses of the composition 37PbO–8Al 2 O 3 / Sc 2 O 3 / Y 2 O 3 −54SiO 2 : 1Ho 2 O 3 (Holimium series), 37PbO–8Al 2 O 3 / Sc 2 O 3 / Y 2 O 3 −54SiO 2 : 1Er 2 O 3 (Erbium series) and 37PbO–8Al 2 O 3 / Sc 2 O 3 / Y 2 O 3 −54SiO 2 : 0.5Ho 2 O 3 +0.5 Er 2 O 3 (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 Y 2 O 3 . 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 Y 2 O 3 . 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 Al 3+ , Sc 3+ and Y 3+ are expected to be coordinated by three SiO 4 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 Y 3+ ions silicate tetrahedra must be moved more outward since the ionic radius of this ion is more when compared with that of Al 3+ and Sc 3+ ions. In view of this, although three ions are linked in triangle with SiO 4 structural units, the octahedra of yttrium ion is more distorted when compared with that of the other two ions