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Spectroscopy and enhanced frequency upconversion in Nd3+-Yb3+ codoped TPO glasses: energy transfer and NIR to visible
Mohd Azam1, Vineet Kumar Rai1, Deepak Kumar Mohanty2
1Laser and Spectroscopy Laboratory, Department of Applied Physics, Indian Institute of Technology (ISM), Dhanbad (826004), Jharkhand, India.
Abstract:
TeO2-Pb3O4 (TPO) glasses codoped with Nd3+ and Yb3+ ions have been fabricated by conventional melting technique. The absorption, emission and excitation spectra of the samples have been recorded. The optical band gap in both the doped/codoped glasses is found to be ∼3.31 eV. Judd-Ofelt analysis has been carried out by using the absorption spectrum of 0.8 mol% Nd3+ doped glass to determine the radiative properties viz radiative transition probabilities, branching ratios, radiative lifetimes, quality factor and emission cross sections of some emitting levels for Nd3+ ions. The radiative transition probability for the 4G7/2 → 4I9/2 transition (∼1926 Hz) is found to be maximum compared to other 4G5/2 → 4I9/2 (∼1622 Hz) and 4F5/2 → 4I9/2 (∼865 Hz) transitions. Upconversion (UC) luminescence of the samples has been examined by the 980 nm CW diode laser excitation. Effect of addition of Yb3+ ions in the Nd3+ doped glasses on UC emission intensity has been discussed. The UC emission intensity corresponding to the green, red and NIR bands in the codoped glass has been enhanced by ∼17, ∼12 and ∼42 times as compared to that of the Nd3+ singly doped glass. The quantum efficiency for the 4G7/2 level is found to be ∼32%. The nephelauxetic ratio, bonding parameter and covalency of Nd3+ ions have been found positive which represents the covalent bonding between Nd3+ ion and oxygen atom. The colour tunability from yellowish-green to dominant green region has been obtained in the optimized codoped TPO glass.
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