Hetero-valent substitution strategy toward orange-red luminescence in Bi3+ doped layered perovskite oxide phosphors for high color rendering index white light-emitting diodes
The equivalent or hetero-valent substitution strategy is an efficient method for stimulating photoluminescence tuning or optimizing the photoluminescence performances of phosphor materials. A new K 2 NiF 4 -type layered perovskite SrLaZnO 3.5 :Bi 3+ phosphor with broad-band yellow emission (558 nm) is first explored. Based on an efficient hetero-valent substitution strategy, a series of Sr 1- x La 1+ x ZnO 3.5+ x /2 :Bi 3+ (0 ≤ x ≤ 0.4) solid solution phases are successfully constructed. The different Bi 3+ local environments at two crystallographic sites and vacancy oxygen make the various distributions of emission and excitation spectra. Consecutive emission tuning from yellow (558 nm) to orange (585 nm), and improvement of emission intensity and internal quantum efficiency (IQE = 45%-64%) are achieved through La 3+ hetero-valent substitution for Sr 2+ in Sr 1- x La 1+ x ZnO 3.5+ x /2 :Bi 3+ (0 ≤ x ≤ 0.4). The structural stability and Bi 3+ occupation distribution in solid solution have been revealed by structural elaboration and crystal field regulation. Based on the both hetero-valent substitution and site-selective excitation strategies, a novel orange-red luminescence can be observed peaking at ~609 nm under near-ultraviolet light (~390 nm) excitation without visible absorption. The fabricated full-spectrum phosphor-converted white light-emitting diodes (pc-WLEDs) show outstanding warm white light, and a high color rendering index (Ra = 97.1, R9 = 98) is achieved, implying that the as-prepared Sr 1- x La 1+ x ZnO 3.5+ x /2 :Bi 3+ (0 ≤ x ≤ 0.4) phosphors can used as yellow/orange-red components in pc-WLED lighting. These results indicate that hetero-valent substitution can predict and control site preference of luminescent centers, providing a new way for optimizing phosphor materials for solid-state lighting.
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