Development of Eu3+ doped bismuth germanate glasses for red laser applications

The intense red-emitting Eu3+ doped bismuth germanate glasses have been prepared by melt quenching technique with the chemical composition of (100-x)(0.2Bi(2)O(3)-0.8GeO(2))-xEu(2)O(3) (x = 0.5-2 mol%). Spectroscopic analysis have been performed through FTIR, absorption, luminescence and decay time measurements to enlighten the structural and optical properties of these systems. The bonding parameter (delta) and optical band gap (E-g) of prepared glasses have been calculated from the optical absorption spectra. Phonon side band spectroscopy was used to explore the phonon energy, electron-phonon coupling strength and multiphonon relaxation rate of Eu3+ doped bismuth germanate glasses. Under near UV excitation at 393 nm enhanced red emission is observed at 611 nm (D-5(0) -> F-7(2)) with rising Eu3+ content. The radiative properties including transition probability (A), branching ratio (beta(R)), stimulated emission cross-section (sigma(e)) and decay time (tau(R)) for different excited states have been evaluated by using Judd-Ofelt parameters determined from the emission spectra. The calculated values of asymmetric ratio (R/O) and Omega(2) suggest high asymmetric environment for Eu3+ ions and high covalency for Eu-O bond which are also confirmed by positive values of bonding parameter. The decay curves of D-5(0) -> F-7(2) transition were well fitted to single exponential function for all the concentrations. The slight increase in decay times with rising Eu3+ ion content is due to the increase in the asymmetry of the local environment at the Eu3+ ion site. The CIE color coordinates (x,y) of the prepared glasses are within the range of 0.637-0.648 and 0.347-0.350 and are very close to the standard red color (0.67, 0.33) suggesting pure intense red emission is achieved. The results indicate that BGEx glasses are promising materials for red laser applications.