Stable Blue-Cyan Photoluminescence from Tendentious Multisite Occupations of Bi3+ in NaBaScSi2O7 with Efficient Absorption in nUV for Application in “Healthy” Illumination and Field Emission Display

In the view that Bi³⁺ has wide absorption in the near-ultraviolet (nUV) electromagnetic spectrum and scarcely absorbs in the visible region, incorporation of Bi³⁺, instead of the extensively adopted Eu²⁺/Ce³⁺, in lattice sites of a host is quite meaningful for wide applications. Herein, we report a fresh phosphor, composed of cationic-rich scandium silicate NaBaScSi₂O₇ as a host and dopant Bi³⁺ (NBSS: Bi), in which high efficiency/stable blue-cyan photoluminescence (PL) is gained via Bi³⁺ concentration doping-induced site-selective occupation from the beginning of the majority at the Na⁺ site to both Na⁺/Ba²⁺ sites. Unlike Eu²⁺/Ce³⁺ that usually exhibits longwave PL with relatively low efficiency absorption in the nUV region and inevitably causing nUV light leak and poor color rendering, the NBSS: Bi shows highly efficient absorption in nUV and quantum efficiency (QE). The PL with a broad full width at half maximum in the blue-cyan region also helps to avoid a ‘cyan gap’ for ‘healthy’ full-visible-spectrum illumination. To improve the PL QE, the effect of a monovalent charge compensator (Li or K) acting as both a flux to enhance crystallinity and charge compensator to decrease defects induced by heterovalent substitution is examined/compared in NBSS: Bi/K (Li). A promising alkaline-earth-metal-ion blending strategy (Sr → Ba) is also proposed to achieve higher QE in NB(S)SS: Bi/K. By further codoping the green-emitting of Tb³⁺ and the red PL of Eu³⁺ via energy transfer from Bi³⁺ to Tb³⁺/Eu³⁺ in NB(S)SS: Bi/Tb/Eu/K, a ‘warm’ phosphor-converted white-light-emitting diode (pc-wLED) with high efficiency/stability and excellent CRI (especially R₆/R₇, associated with a supplement from shortwave blue light) is realized via a remote ‘capping’ packaging strategy. Meantime, cathodoluminescence behaviors of the NB(S)SS: Bi/K also show a high saturation current/voltage with splendid color stability under low voltage, indicating its possibility for application in field emission displays.