Emission-tunable Ba2Y1–xScxNbO6:Bi3+ (0 ≤ x ≤ 1.0) phosphors for white LEDs

Abstract

Here, we report a series of Bi3+-doped Ba2Y1–xScxNbO6 (0 ≤ x ≤ 1.0 mol) phosphors by using the traditional high temperature solid-state reaction. To achieve the structural and photoluminescent (PL) information, several experimental characterizations and theoretical calculations were carried out, including X-ray diffraction (XRD), Rietveld refinement, UV-visible diffuse reflectance and PL spectra, temperature dependent PL spectra, and density functional theoretical (DFT) calculations. The XRD results show that the Bi3+-doped Ba2Y1–xScxNbO6 samples belong to the double-perovskite phase with a cubic space group of Fm3̅m, and the diffraction positions shift toward high diffraction angle when the larger Y3+ ions are gradually replaced by the smaller Sc3+ ions. In addition, the refined XRD findings show that the Bi3+ ions tend to substitute the Y3+ and Sc3+ sites in the Bi3+-doped Ba2Y1–xScxNbO6 (0 <x < 1.0 mol) solid solutions. The PL spectra show that the emission positions of the solid solution samples tune from 446 to 497 nm with the increase of Sc3+ content, which can be attributed to the modification of crystal field strength around Bi3+ ions. Moreover, there is energy transfer from the Ba2YNbO6 host to Bi3+ ions, which is dominated by a resonant type via a dipole-quadrupole (d-q) interaction. The Ba2Y0.6Sc0.4NbO6:0.02 molBi3+ shows the strongest PL intensity under 365 nm excitation, with the best quantum efficiency (QE) of 68%, and it keeps 60% of the room temperature emission intensity when the temperature increases to 150 °C, meaning that the Ba2Y0.6Sc0.4NbO6:Bi3+ features excellent thermal quenching of luminescence. By combining this optimal sample with a commercial red-emitting Sr2Si5N8:Eu2+ phosphor, and a commercial 365 nm UV LED chip, a white LED device, with the color temperature (CT) of 3678 K, color rendering index (CRI) of 67.9, and CIE coordinates at (0.371, 0.376), is achieved.