NIR luminescence and energy transfer kinetics in Nd3+/Yb3+ co-doped sodium aluminium bismuth fluoro-borosilicate glasses

Abstract

Here, we demonstrate the results pertaining to energy transfer kinetics in Nd3+/Yb3+ ions combinedly doped in oxy-fluoride based sodium aluminum bismuth fluoro-borosilicate glasses. The thermal stability for the parent NABFBS glass is evaluated from TG-DTA measurement, and Raman & FT-IR spectral profiles were investigated to realize the influence of phonon energy of host NABFBS glass and OH− content on luminescence features of Nd3+ and Yb3+ ions. Upon pumping at 808 nm, Nd3+ glasses displayed intense NIR emission for 1 mol% concentration at 903, 1068 and 1348 nm labeled to corresponding transitions 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2. Effect of multiphonon-, cross-relaxation and OH− group on Nd3+ emission causing luminescence quenching above 1.0 mol % Nd3+ is interpreted. The sensitizing effect of Nd3+ emission on Yb3+ luminescence is investigated by co-doping Nd3+ ion (optimized to 1 mol%) with different Yb3+ ion concentrations. The probability of energy-transfer (ET) between these ions has been substantiated by the considerable spectral overlap of Yb3+ absorption and Nd3+ emission, luminescence features, emission decay rates and energy level diagram. On co-doping Yb3+ to Nd3+, the emission intensity of Yb3+is enhanced along with simultaneous decrement in Nd3+ emission owing to transfer of Nd3+ excitation energy. This process is further supported by the shortening of Nd3+ life-times in co-doped glasses compared with individually Nd3+ doped glasses. The probability of transfer of energy in Nd3+ and Yb3+ combinedly doped system is estimated along the same lines of Dexter's theory and Inokuti-Hirayama (I-H) fitting model for dipole-dipole coupling. The results reveal that, the energy-transfer mechanism from Nd3+(4F3/2)→Yb3+(4F5/2) is a non-radiative type governed by electric dipole-dipole interaction with phonon assistance. The energy transfer parameters, donor-acceptor coupling constant (CDA), energy-transfer efficiency (η) and probability of energy transfer (P) for co-doped glasses are computed from lifetime curves. In addition, back energy transfer Nd3+←Yb3+ is also investigated.