Photoluminescence processes in τ-phase Ba_1.3Ca_0.7- SiO₄:xDy ³⁺/yTb³⁺ phosphors for solid-state lighting

The τ-phase Ba_1.3Ca_0.7- SiO₄:xDy ³⁺/yTb³⁺ phosphors co-doped with Dy ³⁺ (x = 0.03) and Tb³⁺ (y = 0.01-0.05) trivalent rare-earth ions were prepared by the gel-combustion method. The structure-property relation of the samples was examined by X-ray diffraction, scanning electron microscopy and spectrophotometer. Here, the effect of Tb³⁺'s concentration on the spectroscopic properties of Ba_1.3Ca_0.7- SiO₄:xDy ³⁺/yTb³⁺ phosphors was explored by using the photoluminescence excitation, emission and decay curves. Importantly, the photonic energy transfer from (Dy ³⁺:⁴F_9/2 + Tb³⁺:⁷F₆) to (Dy ³⁺:⁶H_15/2 + Tb³⁺:⁵D₄) was observed, in which the Dy ³⁺ ions act as a light-emitting donor whereas the Tb³⁺ ions as a light-absorbing acceptor, resulting in an enhanced emission from the co-doped Ba_1.3Ca_0.7- SiO₄:xDy ³⁺/yTb³⁺ (x = 0.03 and y = 0.01-0.05) phosphors. Finally, the chromaticity coordinates were determined from the measured emission spectra, locating at the green and white light regions. This observation indicates that the characteristic emission colour could be tuned from white to green by varying Tb³⁺ concentrations under ultraviolet light.