Emission color tunability of dysprosium-activated YNbO4–LuNbO4-mixed phosphors.

Herein, we demonstrate the photoluminescence properties of Dy³⁺-activated YNbO₄, LuNbO_4, and mixed Y_xLu_1−xNbO₄:Dy³⁺ (x = 0.25, 0.5, 0.75) phosphors. For this purpose, five samples with a fixed Dy³⁺ concentration (2 mol%) were prepared by the solid-state reaction method. X-ray diffraction measurements showed that all phosphors crystallize in a monoclinic fergusonite-beta-(Y) structure with a C2/c space group. Scanning electron microscopy clearly shows that samples are composed of dense, well-developed micron-sized, cube-shaped grains with rounded edges. The photoluminescent emission spectra feature Dy³⁺ peaks at standard positions corresponding to transitions from the ⁴F_9/2 excited emitting level to the ⁶H_J (J = 15/2; 13/2; 11/2 and 9/2) lower levels with two dominant emission bands placed in the blue (~ 479 nm, B) and yellow (~ 576 nm, Y) spectral region. It is observed that with Lu increase in the host lattice Y/B ratio decreases toward the desired ratio of unity to obtain white light. To evaluate the suitability of these phosphors for use in solid-state lighting, their photoluminescence emission was analyzed in detail by calculating CIE coordinates, correlated color temperature (CCT) and Delta u,v (DUV). It is shown that CIE chromaticity coordinates of all Dy³⁺-activated Y_xLu_1−xNbO₄ samples (x = 0, 0.25, 0.5, 0.75, and 1) fall into the white portion of the diagram and that with the increase of Lu in the host lattice color becomes whiter. CCT values for all samples are in the cooler 4000–4500 K range with positive DUVs indicating that color points are placed above the black body curve. The average lifetime of ⁴F_9/2 level is calculated to be ~ 0.2 ms for all Dy³⁺-activated Y_xLu_1−xNbO₄ samples, indicating that there is no influence of the Y-to-Lu ratio in the host niobate material on the luminescence kinetics. [ABSTRACT FROM AUTHOR]