Jilin Zhang

Applications of stimuli‐responsive metal halides are often constrained by their inherent trade‐off between high response sensitivity and long‐term environmental stability. In this work, by partial incorporation of Cl ⁻ into C ₅ H ₁₁ N ₃ MnBr ₄ (C ₅ H ₁₁ N ₃ ²⁺ = histamine cation), overall structural rigidity and local structural flexibility are successfully integrated within one metal halide, thus leading to the dual optimization of photophysical and responsive performance. The obtained mixed halide, C ₅ H ₁₁ N ₃ MnCl ₃ Br, exhibits markedly improved resistance to both thermal treatment and continuous UV irradiation, as well as a 1.5‐fold increase in photoluminescence quantum yield. Concurrently, the mixed halide exhibits a humidity‐triggered emission color transition from green to red. This transition cannot be reversed unless heated to at least 80°C, demonstrating a unique humidity history memory function, which is highly suitable for humidity contamination monitoring in long‐distance shipping. This work highlights the role of halide ions mixing in activating responsive performance, which has been rarely reported, and provides a new structural regulation strategy to harmonize luminescence efficiency, environmental stability, and stimuli‐responsive functionality in metal halides.

White light‐emitting diodes (LEDs) demand phosphors with efficient near‐ultraviolet (NUV) excitation and high color rendering. Herein, NaGdSiO ₄ :Eu ^2+/3+ phosphors were synthesized via a high‐temperature solid‐state method. Under 365/396 nm NUV excitation, they exhibit a broadband yellow emission (470–740 nm, 545 nm peak, a full‐width at half maximum (FWHM) of 140 nm) from Eu ²⁺ occupying Na ⁺ and Gd ³⁺ sites, complemented by Eu ^{3 +} ’s red sharp peaks. The phosphors show homogeneous elemental distribution. Introduction of Li ₂ CO ₃ as flux enhances emission intensity and thermal stability, obviously. A prototype pc‐LED device (365 nm chip + NaGdSiO ₄ :Eu ^2+/3+ + BAM:Eu ²⁺ ) achieves a high color‐rendering index (CRI = 91.7), outperforming commercial Y ₃ Al ₅ O ₁₂ :Ce ³⁺ (YAG:Ce ³⁺ )‐based LEDs (CRI = 74.6). These results demonstrate NaGdSiO ₄ :Eu ^2+/3+ ’s potential as a high‐CRI phosphor for high‐quality white LEDs.

White light‐emitting diodes (WLEDs) based on near‐ultraviolet (n‐UV) chips exhibit superior spectral stability and health lighting compared to those based on blue chips. Eu ²⁺ ‐activated nepheline phosphors can efficiently emit broad green light when excited by n‐UV light, showing potential for WLED applications. Traditional high‐temperature solid‐state methods can only control solid solution formation between NaAlSiO ₄ and Na ₃ K(AlSiO ₄ ) ₄ , failing to address the issue that Eu ²⁺ ions occupy two cation sites simultaneously. By utilizing 3A zeolite with a high K/Na ratio as raw material, K‐rich Eu ²⁺ ‐activated nepheline phosphors are successfully synthesized. This enabled Eu ²⁺ to solely occupy MO ₈ sites and emit broad green light ≈526 nm. The optimal phosphor 3A‐1400: 0.06Eu ²⁺ exhibited internal and external quantum efficiencies as high as 92.85% and 76.70%, respectively, with emission intensity retention exceeding 86% at 423 K compared to room temperature, demonstrating excellent thermal stability. By combining this green phosphor with commercial blue and red phosphors, phosphor‐converted WLED (pc‐WLED) devices are fabricated on 380 and 395 nm n‐UV chips, yielding warm white light with color rendering indices of 88.0 and 86.8, and luminous efficacies of 71.7 and 55.7 lm W ⁻¹ , respectively. These findings underscore the significant potential of the synthesized K‐rich Eu ²⁺ ‐activated nepheline phosphors in n‐UV‐based pc‐WLEDs.

Luminescence of transition metal ions in unusual oxidation states is a treasure for developing new phosphors. Pentavalent manganese (Mn⁵⁺), which possesses a 3d² electron configuration, has been reported less compared to its Mn²⁺ and Mn⁴⁺ counterparts due to the difficulty in its stabilization. In this study, Ba₂(Si_1-xGe_x)O₄:Mn⁵⁺ phosphors were synthesized by a solid-state reaction method. The successful Mn⁵⁺ stabilization in the (Si,Ge)O₄ tetrahedron leads to a bright turquoise body color with a strong NIR-II sharp-peak emission at room temperature. By replacing Si⁴⁺ with Ge⁴⁺, the peak position of the ¹E-³A₂ transition remains at 1181 nm, while the corresponding integrated intensity is enhanced by 150% at x = 0.6. First-principles density functional theory (DFT) calculations were performed to explore the geometrically optimized structure and electronic structure variation of the Ba₂(Si,Ge)O₄:Mn⁵⁺ phosphor. Then, they are discussed in association with the observed luminescence properties. It is found that modification of the host composition could modify the accelerated thermal quenching rate of the ¹E emission. Temperature can be read from Mn⁵⁺¹E vs ³T₂ luminescence intensity ratios. This work represents a step toward exploring the unusual Mn⁵⁺ as the emitting center for the next-generation NIR-II phosphors and chromophores for new pigments.

The review provides an overview of strategies to enhance the stability of Eu²⁺- and Ce³⁺-activated phosphors with anti-/zero thermal quenching, and discusses potential research directions for achieving thermally stable phosphors.