Raman, Judd-Ofelt, and photoluminescence analysis of Ho3+/Yb3+-doped borotellurite glasses for potential laser applications

In this study, glasses with the composition (79-x) B2O3-xTeO2-20Li2O-0.5Ho2O3-0.5Yb2O3 (x = 0-50 mol%) were synthesized using the melt-quenching method to explore the spectroscopic effect of TeO2 and B2O3 as mixed glass formers. Raman spectroscopy indicated that increasing TeO2 content leads to depolymerization, characterized by a reduction in the relative area of TeO4 units. Absorption spectra revealed nine peaks related to transitions from 5I8 ground state to various excited states of Ho3+ ions, and one peak for the transition from the 2F7/2 ground state of Yb3+ ions. A negative bonding parameter suggests that there is primarily ionic interaction among Ho3+ and its ligands. However, the increase of Omega 2 suggests that Ho3+ ions have relatively higher covalence and strong ligand polarizability, except at x = 40 mol% due to the rivalry among TeO2 and B2O3. Decrease in Omega 4 and Omega 6 reflect reduced glass rigidity due to increased NBO content, weakening the glass structure. Luminescence spectra showed green (526 nm) and red (642 nm) emissions from Ho3+ transitions of 5F4 -> 5I8 and 5F5 -> 5I8. Intriguingly, a novel peak at 738 nm associated with the 5F4 -> 5I7 transition in Ho3+ ions, linked to energy transfer from Yb3+ to Ho3+. The stimulated emission cross section for the green and red emission were (0.324 - 0.347) x 10- 20 cm2 and (0.387 - 0.423) x 10- 20 cm2 respectively. These glasses demonstrate potential for advanced laser, green display, and photonic technology applications.