UV/blue upconversion in Nd3+:TeO2 glass, effect of modifiers and heat treatment on the fluorescence bands

Upconversion (UC) emissions in UV/blue region have been observed in Nd3+ doped tellurite glass on 532 nm excitation. The UC bands have been observed at 360, 387, 417 and 452 nm due to the 4D3/2 → 4I9/2, 4D3/2 → 4I11/2, 4D3/2 → 4I13/2 and 4D3/2 → 4I15/2 transitions, respectively and they show two photon character. The effect of BaCO3, BaF2 and BaCl2 glass modifiers on the UC efficiency has been studied and Judd-Ofelt intensity parameters have been calculated and compared. The BaCl2 modified glass showed maximum UC intensity among the three modifiers and this enhancement in UC intensity has been related to the reduction in average phonon frequency of the glass sample. Heat treatments of the BaF2 and BaCl2 modified samples also show enhancement in UC intensity while the BaCO3 modified sample has no such effect. Lifetime of the 4D3/2 level has been measured to understand the mechanism responsible for UC emission. Temperature dependent fluorescence studies have been done on the 4F3/2, 4F5/2 and 2S3/2 emitting levels and results show that Nd3+ doped tellurite glass can be used as a temperature sensor.