Stable Blue-Cyan Photoluminescence from Tendentious Multisite Occupations of Bi³⁺ in NaBaScSi₂O₇ with Efficient Absorption in <i>n</i>UV 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.