New fluorophosphate glasses co-doped with Eu3+ and Tb3+ as candidates for generating tunable visible light

A series of optically active Eu3+ and Tb3+ doped fluorophosphate glasses with compositions (BaF2)0.25(SrF2)0.25(AlF3)0.10[Al(PO3)3]0.20(YF3)0.20-x(EuF3 and/or TbF3)x (x = 0 to 0.04) was prepared and characterized by optical spectroscopy. While embedded in the oxyfluoride host, the cited rare earth (RE) ions exhibit improved spectroscopic properties such as longer excited state lifetimes than in oxide glasses and intense emissions in the red (5D0 → 7F2, Eu3+), green and blue (5D4 → 7F5 and 5D3,5G6 → 7F5,7F4, Tb3+) spectral regions. Based on this fact, co-doped samples can be designed with appropriate concentrations of these two ions and generate tunable and white light upon excitation with suitable wavelengths, dispensing the need for a third blue emitting RE ion. Four co-doped samples with equal amounts of EuF3 and TbF3 and total concentration of 0.3, 0.5, 1.0 and 1.5 mol% were tested. Their CIE chromaticity coordinates were calculated for various excitation wavelengths in the region from 350 to 360 nm allowing tuned emission from blue to red. The long lifetime values of the emitting levels in these co-doped samples (τ ≈ 3.1 ms for Eu3+5D0, and τ ≈ 4.0 ms for Tb3+5D4), associated with fairly high quantum yields (Q.Y. = 5-12%) of the samples indicate that these materials could be efficiently pumped by high power LEDs around 355 nm.