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Developing violet‐light‐excitable deep‐red (650–660 nm) Eu2+‐activated phosphor is essential for full‐spectrum lighting. However, the related phosphors with facile synthesis, excellent optical performance, and superior thermal stability are scarce. Herein, a new class of (Sr,Ba)Lu2O4: Eu2+ deep‐red phosphor (660 nm) excitable by violet light via Ba2+‐induced local structure engineering is reported. Impressively, tunable emission from 615 to 682 nm, accompanied by significant improvement of thermal stability (81%@423 K), is achieved by partially substituting Sr2+ by Ba2+ in SrLu2O4: Eu2+. Crystal field analysis, density functional theory calculations, and thermoluminescence spectra confirm that the strong distortion and enhanced covalency of [EuO6] octahedron are responsible for spectral tunability, and the formation of shallow trapping states is beneficial for electron compensation to inhibit thermal quenching in the Sr0.85Ba0.15Lu2O4: Eu2+ phosphor. Finally, a white light‐emitting diode prototype fabricated by coupling of the Sr0.85Ba0.15Lu2O4: Eu2+ deep‐red phosphor and commercial blue/green phosphors with violet chip can yield sunlight‐like white light with an ultra‐high color rendering index (Ra = 95.2, R9 = 97.0) and an appropriate correlated color temperature of 4121 K, verifying its significant application potential in full‐spectrum solid‐state lighting. [ABSTRACT FROM AUTHOR]

The "cyan gap" is the bottleneck problem in violet-driven full-spectrum white-light-emitting diodes (wLEDs) in healthy lighting. Accordingly, we develop a novel broadband-blue-cyan emission Na 3 KMg 7 (PO 4 ) 6- x (BO 3 ) x :Eu 2+ (NKMPB:Eu 2+ ) phosphor via crystal-site engineering. This phosphor is derived from the Na 3 KMg 7 (PO 4 ) 6 :Eu 2+ phosphor, which shows desired abundant cyan emissive components. A comparative study is conducted to reveal the microstructure-property relationship and the key influential factors to its spectrum distribution. It can be found that the introduced (BO 3 ) 3- units can manipulate the site-selective occupation of Eu 2+ activators, asymmetrically broadening the emission spectrum in NKMPB:Eu 2+ . Considering detailed luminescence performance analysis and the density functional theory calculations, a new substitution pathway of Eu 2+ is created by substituting (PO 4 ) 3- with (BO 3 ) 3- units, making partial Eu 2+ ions enter the Mg 2+ (CN = 5, CN = 6) crystallographic sites, and yielding an extra emission band at 600 nm (16667 cm -1 ) and especially 501 nm (19960 cm -1 ). Meanwhile, a high-color-quality full-spectrum-emitting wLEDs was fabricated, upon 100 mA forward-bias current driven. Due to the achieved extra cyan emissive components of NKMPB:Eu 2+ , the constructed NKMPB:Eu 2+ -based wLEDs show better color rendering ability (∼90.9) than that of Na 3 KMg 7 (PO 4 ) 6 :Eu 2+ -based wLEDs (∼86.3), and also demonstrate its great potential in full-spectrum healthy lighting.