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

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.