Light-Induced Charge Transfer to Achieve Deep-Red Emission in SrSc₂O₄:Bi toward Multiple Optical Applications

Bismuth (Bi) is used for luminescent materials due to its unique optical performance, but deep-red light from Bi-doped materials is rarely reported. In particular, establishing a design principle for Bi-doped red materials is considered to be a significant challenge. Herein, using a deep-red SrSc2O4:Bi material featuring Bi–Bi pair emission, light-induced charge-transfer from BiSc3+–BiSr3+ to BiSc4+–BiSr2+ enables the realization of Bi2+2P3/2(1) → 2S1/2 deep-red emission. Intriguingly, SrSc2O4:Bi displays an excellent zero-thermal-quenching performance from 298 to 423 K, with a peak intensity that retains 98% of the intensity at 298 K and an integrated intensity at 423 K that even reaches 110% of the initial intensity. The intriguing spectroscopic characteristics of SrSc2O4:Bi make it a promising candidate in the agricultural field, night-vision security, and the medical treatment area. This work advances the understanding of red luminescence in Bi-activated luminescent materials and thus can initiate more exploitation of red materials for emerging applications

Highly Efficient Narrow-Band Green-Emitting Na₃K₅(Li₃SiO₄)₈:Eu²⁺ Phosphor with Low Thermal Quenching

In the pursuit of high efficiency and wide color gamut in displays, there is still an urgent demand for high-performing narrow-band green-emitting phosphors. Inspired by a mineral UCr4C4-type structure with a highly condensed framework, a novel narrow-band green-emitting Na3K5(Li3SiO4)8:Eu2+ (NKLSO:Eu2+) phosphor is designed. This phosphor exhibits a green emission peaking at 525 nm with a full width at half-maximum (fwhm) of 43 nm. The narrow-band emission is associated with the highly symmetric sites for Eu2+. Benefiting from its high structural rigidity, this NKLSO:Eu2+ phosphor shows a very low photoluminescence (PL) thermal quenching, maintaining 96%@150 °C integrated PL intensity of the original PL intensity. Moreover, by incorporating a small amount of Al3+ into the lattice, the internal quantum efficiency (QE) and external QE of this phosphor is enhanced from 70 to ∼100% and 21 to 38%, respectively. The as-fabricated wLED-1 (InGaN chip@blue, NKLSO:1.25% Eu2+@green, KSiF6:Mn4+@red) shows a wide color gamut (106% NTSC), demonstrating vivid photographs when used in a projector. The as-fabricated wLED-4 (BaMgAl10O17:Eu2+@blue, NKLSO:1.25% Eu2+@green, CaAlSiN3:Eu2+@red) presents a low correlated color temperature of 5390 K and a high color rendering index (Ra) of 86.9. These results show that narrow-band green-emitting NKLSO:Eu2+ has potential applications in both backlight displays and solid-state lighting

Full Color Luminescence Tuning in Bi³⁺/Eu³⁺-Doped LiCa₃MgV₃O₁₂ Garnet Phosphors Based on Local Lattice Distortion and Multiple Energy Transfers

In the pursuit of high-quality W-LED lighting, the precise control of emission color of phosphor materials is indispensable. Herein we report a series of single-composition Bi³⁺-doped LiCa₃MgV₃O₁₂ garnet-structure phosphors, whose emission colors under n-UV excitation could be tuned from bluish green (480 nm) to yellow (562 nm) on the basis of local lattice distortion and VO₄^3– → Bi³⁺ energy transfer. Furthermore, full-color luminescence tuning from bluish green to orangish red across the warm white light region was successfully achieved by designing VO₄^3– → Bi³⁺ → Eu³⁺ energy transfers. More interestingly, the thermal stabilities of as-prepared samples were gradually enhanced through designing VO₄^3–/Bi³⁺ → Eu³⁺ energy transfers. This work provides a new perspective for color tuning originating from simultaneous local lattice distortion and multiple energy transfers

Highly Efficient Blue Emission and Superior Thermal Stability of BaAl₁₂O₁₉:Eu²⁺ Phosphors Based on Highly Symmetric Crystal Structure

Highly efficient phosphor materials with superior thermal stability are indispensable for phosphor-converted white light-emitting diodes (pc-WLEDs) solid state lighting. In order to obtain a high quality warm white light, near-ultraviolet (n-UV) chips combined with trichromatic phosphors have be extensively studied. Among them, the development of efficient blue phosphor remains a challenging task. In view of the close correlation between 5d–4f transitions of rare earth ions and the coordination environment of host lattice, many studies have been dedicated to improving the photoluminescence performances by modifying the lattice coordination environment including the lattice rigidity and symmetry. In this work, we reported highly efficient blue-emitting Eu²⁺-doped BaAl₁₂O₁₉ (BAO) phosphors with excellent thermal stability, which were prepared via the traditional high-temperature solid state reaction routes. According to the X-ray powder diffraction (XRD) Rietveld refinement analysis, BAO owned a highly symmetric layer structure with two Ba polyhedrons, marked as Ba(1)­O₉ and Ba(2)­O₁₀, respectively. The diffuse reflectance spectra revealed the optical band gap to be 4.07 eV. Due to the suitable optical bandgap, the Eu²⁺ ions could realize a highly efficient doping in the BAO matrix. The photoluminescence excitation (PLE) spectra for as-prepared BAO:Eu²⁺ phosphors exhibited a broad absorption band in the region from 250 to 430 nm, matching well with the n-UV LED chip. Under the UV radiation, it is highly luminous (internal quantum yields (IQYs) = 90%) with the peak around 443 nm. Furthermore, the color purity of BAO:Eu²⁺ phosphors could achieve 92%, ascribing to the narrow full width at half-maximum (fwhm = 52 nm), which was even much better than that of commercially available BAM:Eu²⁺ phosphor (color purity = 91.34%, fwhm = 51.7 nm). More importantly, the as-prepared BAO:Eu²⁺ phosphor showed extra high thermal stability when working in the region of 298–550 K, which was a bit better than that of commercial BAM:Eu²⁺ phosphors. According to the distortion calculation of Ba crystallographic occupation, the superior thermal stability could be attributed to the highly symmetric crystal structure of BAO host. In view of the excellent luminescence performances of BAO:Eu²⁺, it is a promising blue-emitting phosphor for n-UV WLED