Full visible light emission in Eu2+,Mn2+-doped Ca9LiY0.667(PO4)7 phosphors based on multiple crystal lattice substitution and energy transfer for warm white LEDs with high colour-rendering

Abstract

Designing two-step tuning based on substitution of multiple cation lattices and energy transfer successfully achieved versatile colour output for single-phase phosphor-converted white LEDs in this work. Herein, we chose whitlockite-type Ca₉LiY_0.667(PO₄)₇ compound as a host which provides multiple cation sites for Eu²⁺ occupation. Spectral results indicate that the Ca₉LiY_0.667(PO₄)₇:Eu²⁺ phosphor emits a cold white emission due to its multiple emission bands at about 420, 480, and 530 nm, which correspond to emissions from the M(3), M(1)/M(2) and M(5) cation sites as ascertained by the Rietveld refinement method. In order to enhance the red emission of CLYPO:Eu²⁺ phosphors, they were codoped with Mn²⁺. Warm white emission in a single-phase host based on energy transfer was successfully obtained in the CLYPO:Eu²⁺,Mn²⁺ phosphors. The excitation band of the CLYPO:Eu²⁺,Mn²⁺ phosphors in the 360 to 450 nm range perfectly coincides with that of commercial LED chips, implying that these phosphors are desirable for white LED applications. White LEDs with a higher color rendering index (R_a = 90.2) and a lower correlated color temperature (CCT = 3614 K) were achieved by using a single-phase CLYPO:0.03Eu²⁺,0.10Mn²⁺ phosphor and a 395 nm InGaN-LED chip.