Spectroscopic and energy transfer behavior of Dy3+ ions in B2O3-TeO2-PbO-PbF2-Si2O3CdO glasses for laser and WLED applications

A new series of white light emitting Dy3+ doped Lead tellurofluoroborate glasses have been prepared and their spectroscopic and energy transfer behavior were explored through analyzing XRD, FTIR, Raman, SEM, EDAX, optical absorption, photoluminescence and lifetime measurements. The fundamental stretching of the various borate and tellurite networks were identified using FTIR and Raman spectral analysis. The bonding parameter studies reveal the ionic nature of the Dy-O bond in the present glasses. The Judd-Ofelt (JO) intensity parameters determined from the absorption spectra have been used to investigate the nature of bonding and symmetry orientation of the Dy-ligand field environment. The luminescence intensity increases with increasing Dy3+ ion concentration up to 0.5 wt%, beyond that luminescence quenching is observed. The JO parameters have been used to determine the transition probability (A), stimulated emission cross-section (sigma(E)(P)), radiative lifetime (tau(R)) and branching ratios (beta(R)) for the different emission transitions from the F-4(9/2) excited level. The higher sigma(E)(P) and beta(R) values of the F-4(9/2) -> H-6(15/2) and F-4(9/2) -> H-6(13/2) transitions suggest the possible laser action in the visible region. The Y/B ratio, CIE chromaticity color coordinates (x, y) and Color correlated temperature (CCT) were also estimated from the luminescence spectra for different concentration as well as pumping wavelengths. The x, y chromaticity color coordinates fall within the white light region and the white light can be tuned by varying the excitation wavelengths. The lifetime of the F-4(9/2) excited state were measured and is found to decrease with increasing Dy3+ ion content. The non-exponential behavior is predominant in higher Dy3+ ion content glasses and is due to the efficient energy transfer between Dy3+ Dy3+ ions. The decay curves were fitted to the Inokuti-Hirayama (IH) model to understand the nature of energy transfer. Among the prepared glasses, 0.5DPTFB glass possesses higher A, beta(R), sigma(E)(P) eta values and is suggested for lasers and WLED applications. (C) 2014 Elsevier B.V. All rights reserved.