Down conversion and efficient NIR to visible up-conversion emission analysis in Ho3+/Yb3+ co-doped tellurite glasses
Kaniyarakkal Sharafudeen, Kesavulu Culala Rajasekharaudayar, D. Rajesh, Yang Li, Zhi Chen, Vijayakumar Sadasivan Nair, Shiju Edappadikkunnummal
Abstract
A series of glasses with chemical composition (50−x−y) TeO2–30ZnO–10YF3–10NaF–xHo2O3–yYb2O3 (x = 0.5 and y = 0.5, 1.0, 3.0, 5.0 mol%) were prepared by melt-quenching procedure. The absorption spectra, excitation, down conversion emission spectra, up-conversion (UC) emission spectra and decay time measurements were analyzed. In down conversion, the visible emission transition intensity associated with 5F4 → 5I8 (547 nm), 5F5 → 5I8 (657 nm), and 5F4 → 5I7 (755 nm) of Ho3+ ions decreased with Yb3+ concentration due to the energy transfer (ET) process from Ho3+ to Yb3+ ions. In up-conversion, on exciting with 980 nm diode laser beam, we observed a strong green (543 nm) and red (657 nm) UC emissions, that refers to the energy level transitions; 5F4 (5S2) → 5I8 and 5F5 → 5I8 of Ho3+. The influence of excitation power on UC intensities studies revealed that the population at 5F4 (5S2) and 5F5 levels of Ho3+ ion occurs due to two-photon absorption process associated energy transfer from Yb3+ to Ho3+. The influence of Yb3+ doped concentration on UC was studied, and it is observed that both the green and red UC intensities improved significantly on increasing Yb3+ ions concentration.