Concentration-dependent luminescence and energy transfer in Tb3+/Eu3+ doped borate and fluorozirconate glasses

Tb3+ single- and Tb3+/Eu3+ double-doped borate as well as fluorozirconate glasses are investigated for their photoluminescence and energy transfer properties based on the concentration of the dopants. All the double-doped glasses consist of a constant concentration of 0.5 at% Tb3+ ions and an increasing Eu3+ ions concentration, ranging from 0.05 to 0.5 at%. Upon direct excitation of only Tb3+ at 485 nm, the emission spectra of the double-doped glasses demonstrate an enhancement of typical Eu3+ emissions, thus validating the energy transfer from Tb3+ to Eu3+ in both glass systems. While the spectral composition of the emissions of both borate and fluorozirconate glasses are mostly similar, the radiative decay in borate glass is faster than in fluorozirconate glass. The energy transfer efficiency in each glass system is calculated based on the radiative decay measurements. The mechanism of multipolar interaction underlying the energy transfer is determined to be mostly due to dipole-dipole interactions. With increasing Eu3+ concentration, a gradual shift in chromaticity from green to orange/red is observed. Besides the variation in Eu3+ concentration, tunable chromaticity can also be achieved by varying the excitation wavelength.