Broad red-emission of Sr3Y2Ge3O12:Eu2+ garnet phosphors under blue excitation for warm WLED applications

Abstract

Eu²⁺ ions activated Sr₃Y₂Ge₃O₁₂ (SYGO) phosphors were synthesized by an efficient pechini-type sol–gel method. X-ray diffractometry, Fourier transform infrared spectrometry, field-emission transmission electron microscopy, and spectrofluorometry measurements were performed to characterize the prepared phosphor samples after annealing under thermal CO reducing atmosphere. The phosphors showed nearly spherical-shaped morphology and their phase was identified to be cubic with the space group lad (230). Under 468 nm blue excitation, the SYGO:Eu²⁺ phosphors exhibited a broadband red emission at 612 nm due to the 4f⁶5d¹ → 4f⁷ electronic transition of Eu²⁺ ions. Temperature-dependent photoluminescence (PL) emission properties, PL decay profile and quantum yield were measured for the optimized SYGO:0.01 mol Eu²⁺ (SYGO:0.01Eu²⁺) red phosphor. Furthermore, a white light-emitting diode (WLED) device was also fabricated by blending the SYGO:0.01Eu²⁺ red phosphor with a commercially available Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) yellow phosphor on a 452 nm blue LED chip under 30 mA forward-bias current. The fabricated YAG:Ce³⁺/SYGO:0.01Eu²⁺-based WLED device showed Commission International de I'eclairage chromaticity coordinates in the natural white region (0.3300, 0.3439) with good color rendering index and correlated color temperature of 85.81 and 5483 K, respectively. These results imply that the SYGO:0.01Eu²⁺ is a potential red phosphor to obtain the warm white light under blue excitations.