Red phosphor materials play a key role in improving the lighting and backlit display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the development of a red phosphor with simultaneous high efficiency, excellent thermal stability and high colour purity is still a challenge. In this work, unique non-concentration quenching in solid-solution Cs3Gd1 − xGe3O9:xEu3+ (CGGO:xEu3+) (x = 0.1–1.0) phosphors is successfully developed to achieve a highly efficient red-emitting Cs3EuGe3O9 (CEGO) phosphor. Under the optimal 464 nm blue light excitation, CEGO shows a strong red emission at 611 nm with a high colour purity of 95.07% and a high internal quantum efficiency of 94%. Impressively, this red-emitting CEGO phosphor exhibits a better thermal stability at higher temperatures (175–250 °C, >90%) than typical red K2SiF6:Mn4+ and Y2O3:Eu3+ phosphors, and has a remarkable volumetric negative thermal expansion (coefficient of thermal expansion, α = −5.06 × 10−5/°C, 25–250 °C). By employing this red CEGO phosphor, a fabricated pc-WLED emits warm white light with colour coordinates (0.364, 0.383), a high colour rendering index (CRI = 89.7), and a low colour coordinate temperature (CCT = 4508 K). These results indicate that this highly efficient red-emitting phosphor has great potential as a red component for pc-WLEDs, opening a new perspective for developing new phosphor materials.

Recently, there has been growing interest in developing Bi3+-activated luminescence materials for optoelectronic applications. Herein, new yellow/orange-emitting ABZn2Ga2O7:Bi3+ (ABZGO, A = Ca, Sr; B = Ba, Sr) phosphors with tunable optical properties are synthesized by an alkaline earth cation substitution. When Sr2+ substitutes Ca2+ and Ba2+, the excitation wavelength has a red shift from 325 to 363 nm, matching well with the n-UV chip based white light-emitting diodes (WLEDs). CaBaZn2Ga2O7:0.01Bi3+ (CBZGO:0.01Bi3+) exhibits two evident emission peaks at 570 and 393 nm originating from the respective occupation of Ca and Ba sites by Bi3+ ions. The optical tuning of the CBZGO:Bi3+ phosphor is achieved by changing the Bi3+ doping content and excitation wavelength based on the selected site occupation. Differently, both SrBaZn2Ga2O7:0.01Bi3+ (SBZGO:0.01Bi3+) and Sr2Zn2Ga2O7:0.01Bi3+ (SZGO:0.01Bi3+) phosphors exhibit a single broad emission band, peaking at 600 and 577 nm, respectively. Two different Bi3+ sites are also verified respectively in SBZGO and SZGO hosts by the Gaussian fitting of the asymmetric PL spectra and lifetime analysis. The different luminescence behaviors of ABZGO:0.01Bi3+ phosphors should be ascribed to the synergistic effect of the centroid shift, crystal-field splitting, and Stokes shift. Moreover, the temperature-dependent PL spectra reveal that cation substitutions of Sr2+ for Ca2+ and Ba2+ can efficiently improve the thermal stability of ABZGO:0.01Bi3+ phosphors. In view of different thermal responses to various temperatures for two emission peaks of the CBZGO:0.01Bi3+ phosphor, an optical thermometer is designed and has a good relative sensitivity (S r = 1.453% K–1) at 298 K. Finally, a WLED with CRI = 97.9 and CCT = 3932 K is obtained by combining SZGO:0.01Bi3+ and BAM:Eu2+ phosphors with a 370 nm n-UV chip, demonstrating that SZGO:0.01Bi3+ is an excellent yellow-orange-emitting phosphor for n-UV WLED devices. This work stimulates the exploration of optical tuning by cation substitution to obtain remarkable luminescence materials for optical temperature sensing and WLED applications.

The development of lead‐free perovskite photoelectric materials has been an extensive focus in the recent years. Herein, a novel one‐dimensional (1D) lead‐free CsMnCl3(H2O)2 single crystal is reported with solvatochromic photoluminescence properties. Interestingly, after contact with N,N‐dimethylacetamide (DMAC) or N,N‐dimethylformamide (DMF), the crystal structure can transform from 1D CsMnCl3(H2O)2 to 0D Cs3MnCl5 and finally transform into 0D Cs2MnCl4(H2O)2. The solvent‐induced crystal‐to‐crystal phase transformations are accompanied by loss and regaining of water of crystallization, leading to the change of the coordination number of Mn2+. Correspondingly, the luminescence changes from red to bright green and finally back to red emission. By fabricating a test‐paper containing CsMnCl3(H2O)2, DMAC and DMF can be detected quickly with a response time of less than one minute. These results can expand potential applications for low‐dimensional lead‐free perovskites.

Near-infrared light-emitting diodes (NIR-LEDs) are potential candidates in food composition analysis, temperature and security monitoring, biometrics, and medical applications. To realize the above objectives, the development of NIR-emitting phosphors is urgently required. Herein, a novel NIR emission is successfully achieved in Bi3+-activated XAl12O19 (X = Ba, Sr, Ca) compounds by constructing the selective site occupation of Bi3+ in Al3+ polyhedra with small coordination number. The designed phosphors exhibit broad-band NIR emission of Bi3+ from 600 to 1000 nm. Interestingly, a broad photoluminescence control from blue to red is also achieved by just changing the sintering atmosphere. The blue emission of Bi3+ should be assigned to the prior occupation in X2+ sites and the existence of oxygen vacancy. This work not only provides a novel insight to develop NIR-emitting Bi3+-activated phosphors but also helps to reveal the underlying NIR luminescence mechanism of Bi3+ in inorganic compounds.

Controllable emission tuning from bluish-green to red was achieved by Ba2+/Sr2+ substitution and Bi3+ → Eu3+ energy transfer.

Thermal quenching (TQ) of phosphor is one of the biggest challenges to develop high‐quality white light‐emitting diodes (w‐LEDs). Herein, an anti‐thermal‐quenching (anti‐TQ) property in cyan‐emitting Ba2ZnGe2O7:Bi3+ phosphor is reported. At 150 °C, its emission intensity increases to 114% of the original intensity at 25 °C. Especially, the integrated emission intensity reaches 138%, 148%, and 134% at 150, 200, and 250 °C, respectively, by artificially creating zinc and oxygen vacancy defect. The anti‐TQ phenomenon is mainly attributed to high structure rigidity and strong ability to compensate emission loss during thermal generation process. Thermal‐induced emission compensation mainly stems from self‐oxidization behavior of Bi2+ in zinc vacancy and the presence of oxygen vacancy defect. Oxygen vacancy is induced by native zinc vacancy and charge imbalance between Bi3+ and Ba2+ ions. The strategy to create oxygen vacancy defect and design self‐oxidization process of Bi opens a new insight to exploit anti‐TQ phosphors for high‐quality w‐LEDs applications.

Highly efficient cyan-emitting phosphor materials are indispensable for closing the cyan gap in spectra of the traditional phosphor-converted white light-emitting diodes (WLEDs) to achieve high-quality full-spectrum white lighting. In this work, bright cyan-emitting Ca 3 Ga 4 O 9 (CGO):0.02Bi 3+ ,0.07Zn 2+ phosphor is developed to bridge the cyan gap. Such a Bi 3+ ,Zn 2+ codoping enhances the cyan emission of CGO:0.02Bi 3+ by 4.1 times due to the influence of morphology and size of phosphor particles, charge compensation and lattice distortion. Interestingly, codoping La 3+ ions into the current system can achieve a photoluminescence tuning of CGO:0.02Bi 3+ from cyan to yellowish-green by crystallographic site engineering. Besides, Bi 3+-Eu 3+ energy transfer is successfully realized in CGO:0.02Bi 3+ ,0.07Zn 2+ ,nEu 3+ phosphors and the emission color tuning from cyan to orange is observed. The investigation of thermal quenching behaviors reveals that the incorporation of Zn 2+ and La 3+ improves the thermal stability of CGO:0.02Bi 3+. Finally, CGO:0.02Bi 3+ ,0.07Zn 2+ ,0.10Eu 3+ phosphor is employed to obtain a single-phased warm WLED device. A full-spectrum WLED device with remarkable color rendering index (Ra) of 97.4 and high luminous efficiency of 69.72 lm W −1 is generated by utilizing CGO:0.02Bi 3+ ,0.07Zn 2+ phosphor. This result suggests the important effect of CGO:0.02Bi 3+ ,0.07Zn 2+ phosphor on closing the cyan gap, providing new insights of cyan-emitting phosphors applied in full-spectrum white lighting.

Controllable cyan-to-orange tuning and optical thermometry in Ba1+xSr1−xGa4O8:Bi3+ phosphors with ultra-broadband emission were realized based on crystal filed control at multiple emission centers.