Double-perovskite Ca2AlNbO6: Mn4+ red phosphor for white light emitting diodes: synthesis, structure and luminescence properties

The red-emitting phosphors Ca2AlNbO6: xmol%Mn4+ (CAN: xmol%Mn4+) (0.1 <= x <= 0.9) were successfully synthesized via a conventional high temperature solid-state method at air atmosphere. A band was located at 320 nm in diffuse reflection spectra (DRS) because of the spin-allowed (4)A(2g) -> T-4(1g) transition of Mn4+. Moreover, there were two broad bands located at photoluminescence excitation (PLE) spectra due to the spin-allowed transitions of Mn4+ upon the excitation of 712 nm. And the phosphors exhibited the far-red emission bands centered at similar to 712 nm on account of the spin-forbidden E-2(g) -> (4)A(2g) transition of Mn4+ under the excitation of 355 nm. And the optimum one was CAN: 0.3 mol%Mn4+ which yields the brightest red light due to the concentration quenching effect. Furthermore, it could be confirmed that the existence of nonradiative among Mn4+ ions because the lifetime of the phosphors was decreased as the concentration of Mn4+ in CAN increased from 0.1% to 0.9 mol%. The average lifetime of the phosphors was in the range of miscroscend. In addition, the CIE chromaticity coordinates of CAN: 0.3 mol%Mn4+ were (0.7319, y = 0.2618). Finally, a blue LED chip combined with YAG: Ce3+ yellow and CAN: 0.3 mol% Mn4+ red phosphors to fabricate a warm white light emitting-diode (WLED). And the CIE chromaticity coordinates, color rendering index (CRI) and the corrected color temperature (CCT) of the device were (0.3799, 0.3432), 74.2 and 3727 K, respectively.