Spectroscopic investigation of Nd3+ single doped and Eu3+/Nd3+ co-doped phosphate glass for solar pumped lasers

We report on the fabrication and characterization of Nd3+ doped phosphate glass to be used as active laser medium for developing solar pumped fiber laser emitting at 1.06 μm. Several Nd3+-doped phosphate glass samples were fabricated, with a host composition of (mol%) 65P2O5:17Li2O:3Al2O3:4B2O3:5BaO:6La2O3 and with a concentration of Nd3+ up to 10 mol%. In order to exploit the unabsorbed solar energy by Nd3+ ions, Eu3+ co-doping of Nd3+-doped phosphate glasses was also investigated to asses a potential increase in the overall pump power conversion efficiency. Physical and thermal properties of single doped and co-doped samples were measured and their spectroscopic properties are discussed. The effect of Nd3+ doping concentration on emission spectra and lifetimes was investigated in single doped samples in order to study the concentration quenching effect on luminescence performance. The shape of the fluorescence spectrum did not change by increasing the Nd3+ doping level while the lifetime of the Nd3+:4F3/2 was found to decrease. The following characteristic value parameters were calculated: radiative lifetime τ0=367 μs and quenching concentration N0= 8.47 E+20 ions/cm3. The Eu3+ co-doping was found to give a limited increase to the glass pump power absorption limited to the UV range. Although energy transfer from Eu3+ to Nd3+occured, a large Eu3+ concentration dependent quenching of Nd3+ fluorescence was observed. This latter process decreases the radiative quantum efficiency of Nd3+:4F3/2 emitting level and hence limits the attractiveness of Eu3+ sensitization for Nd3+ laser action.