Tuning Eu2+ luminescence in Sr8CaLu (PO4)7via Na+-induced local structure engineering for violet-chip-excitable full-spectrum lighting

Abstract

Currently, white light-emitting diodes (wLEDs), designed by combining violet chips (400–420 nm) and multi-color phosphors, are highly desirable for reducing blue light hazard and improving visual comfort. However, green–yellow phosphors with excellent optical performance are scarce so far. Herein, we develop a new type of violet-light-excitable green–yellow Eu²⁺:Sr₈CaLu(PO₄)₇ phosphor with Na⁺ alloying. Benefiting from Na⁺-induced local structural modification, Eu²⁺ luminescence shows gradual red-shifting from 520 nm to 550 nm, with photoluminescence quantum yields (PLQYs) remaining above 70%, decay lifetimes increasing from 1200 ns to 1800 ns, and PL bandwidths enlarging from 110 nm to 172 nm. First-principles density functional theory (DFT) calculations, together with temperature-dependent PL spectra and time-resolved PL spectra analysis, verify the modulation of the proportions of SrO₉, SrO₈ and SrO₆ polyhedra for Eu²⁺ multiple cationic occupation via Na⁺ doping is responsible for the observed PL phenomenon. Finally, we design full-spectrum wLEDs with ultra-high color rendering indexes (CRI, R_a and R10) above 95 by coupling the as-prepared Eu²⁺/Na⁺:Sr₈CaLu(PO₄)₇ phosphor and commercial blue/red phosphors with a violet LED chip, which shows promising applications in healthy solid-state lighting.