Green to white tunable light emitting phosphors: Dy3+/Tb3+ in zinc phosphate glasses

Abstract

Dy3+/Tb3+-doped zinc phosphate glasses of composition in mol.%: 98.0Zn(PO3)2–2.0Dy2O3, (100.0−x)Zn(PO3)2–xTb2O3 and (98.0−x)Zn(PO3)2–2.0Dy2O3–xTb2O3, x = 0.6, 1.0, 2.0 and 5.0, were prepared by conventional melt quenching technique, and characterized by photoluminescence and decay time spectroscopy. The emission color can be adjusted from neutral white of 4279 K (98.0 Zn(PO3)2-2.0 Dy2O3 glass) toward the green region by codoping with Tb3+ from 0.6 to 5.0 mol% of Tb2O3 upon Dy3+ excitation at 392 nm. The Tb3+ emissions (5D4 → 7F6,5,4,3) being sensitized by Dy3+ through a non-radiative energy transfer. Dysprosium 4F9/2 level emissions can also be sensitized through excitation of Tb3+ at 284 nm with an efficiency up to of 80%. Additionally, upon 284 nm excitation dominant 5D4 → 7F5 green emission in detriment of the 5D3 → 7FJ blue one is promoted by a cross relaxation process between Tb3+ and Dy3+ in addition to that among Tb3+ ions. In consequence, the most intense green emission observed in the ZP2Dy5Tb phosphor gives rise to a color purity of 67.8% and chromaticity coordinates (0.29, 0.59) very close to those (0.29, 0.60) of European Broadcasting Union illuminant green. Such cross relaxation processes enhancing the green emission of Tb3+ with ultraviolet excitation might contribute to increment the spectral response of solar photovoltaic cells by down-shifting of the incident solar spectrum.