Enriching red emission of Y_3Al_5O_12: Ce^3+ by codoping Pr^3+ and Cr^3+ for improving color rendering of white LEDs

Triply doped Y3Al5O12: Ce3+, Pr3+, Cr3+ phosphors are prepared by solid state reaction. The emission spectra are enriched in the red region with the luminescence of both Pr3+ and Cr3+ through Ce3+ → Cr3+ and Ce3+ → Pr3+ → Cr3+ energy transfers. The properties of photoluminescence and fluorescence decay indicates larger macroscopic Ce3+ → Cr3+ transfer rates in the triply doped phosphors in comparison to Ce3+ and Cr3+ doubly doped one, reflecting the effect of competition between Ce3+ → Cr3+ and Ce3+ → Pr3+ transfers. White LEDs fabricated using the triply doped phosphor coated on blue LED chips show a color rendering index of 81.4 higher than that either using Ce3+ and Cr3+ doubly doped or Ce3+ singly doped phosphor.