Photoluminescence processes in τ-phase Dy3+/Tb3+-codoped Ba1.3Ca0.7SiO4 phosphors for solid-state lighting

The τ-phase-Ba1.3Ca0.7SiO4 phosphors co-doped with 3 mol% Dy3+ and ~1-5 mol% Tb3+ 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 Dy3+/Tb3+ co-doped Ba1.3Ca0.7SiO4 phosphors was explored by using the photoluminescence excitation, emission, and decay curves. Importantly, the photonic energy transfer from (Dy3+: 4F9/2 + Tb3+: 7F6) to (Dy3+: 6H15/2 + Tb3+:5D4) was observed, in which the Dy3+ ions acts as a light-emitting donor whereas the Tb3+ ions as a light-absorbing acceptor, resulting in an enhanced emission from the co-doped Ba1.3Ca0.7SiO4: Dy3+/Tb3+ 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 color could be tuned from white to green by varying Tb3+ concentrations under ultraviolet light.

Methods
X-ray diffraction (XRD) measurements (Model Philips Bruker D8 advance) were carried out to examine the structure and phase of the prepared phosphor materials. The scanning electron microscope (SEM) (Model JEOL JSM-7800F) was used to characterize the morphology of phosphors as a function of composition. Energy-dispersive X-ray spectroscope (EDX) (Oxford Aztee) was used to confirm the composition of elements in the Ba1.3Ca0.7SiO4: Dy3+/Tb3+ samples. The PL emission and decay spectra were investigated using Cary Eclipse fluorescence spectrophotometer (Model LS-55) equipped with a xenon flash lamp to act as the excitation source.