Down-shifting by energy transfer in Tb3+/Dy3+ co-doped zinc phosphate glasses

An optical spectroscopy investigation of zinc phosphate glasses activated with Tb3+/Dy3+ ions is carried out through photoluminescence spectra and decay time measurements. The emission color can be adjusted from yellow-green light, with CIE1931 chromaticity coordinates (0.36,0.44), toward the white light region (0.35,0.39) by decreasing the Tb3+ content from 1.0 to 0.1 mol% of Tb(PO3)3 upon Dy3+ excitation at 423 nm. Such visible region luminescence is generated by 5D4→7F5 and 5D4→7F3 emissions of Tb3+ in addition to 4I15/2→6H15/2, 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 emissions of Dy3+, so that Tb3+ emission is sensitized by Dy3+ through a non-radiative resonant energy transfer. A dominant 5D4→7F5 green emission is observed in detriment of the 5D3→7FJ blue emissions upon 282 nm excitation, as well as an extended excitation range (280-500 nm), due to multiple Dy3+ and Tb3+ transitions, which might contribute to enhance the spectral response of solar photovoltaic cells by down-shifting of the incident solar spectrum.