Effect of ZnX (X = F2 and Cl2) as modifier on luminescence properties of Ho3+/Yb3+ doped tellurite glasses

Optical absorption and photoluminescent properties of Ho3+/Yb3+ co-doped tellurite and zinc halide tellurite glasses are investigated. The effect of zinc halides as modifier on the luminescence properties of above mentioned samples has been explored. Two intense upconversion emission bands centered at 546 (F-5(4), S-5(2) --> I-5(8)) and 660 (F-5(5) --> I-5(8)) are observed when samples are excited by 976 nm radiation. Zinc halides act as quencher when 976 nm excitation source is used. The up and downconversion emission spectra are recorded with 532 nm excitation source also. In this case also, zinc halides do not show any improvement. The dependence of upconversion intensities on excitation power and temperature is discussed. The power dependence study shows a quadratic dependence of fluorescence intensity on the excitation power while decrement in emission intensity of different transitions at different rates is observed in temperature dependence study. The possible upconversion mechanisms are also discussed in order to understand the energy transfer between Yb3+ and Ho3+ ions. (C) 2011 Elsevier B.V. All rights reserved.