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 Eu 2+ -doped BaAl 12 O 19 (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)O 9 and Ba(2)O 10 , respectively. The diffuse reflectance spectra revealed the optical band gap to be 4.07 eV. Due to the suitable optical bandgap, the Eu 2+ ions could realize a highly efficient doping in the BAO matrix. The photoluminescence excitation (PLE) spectra for asprepared BAO:Eu 2+ 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:Eu 2+ phosphors could achieve 92%, ascribing to the narrow full width at halfmaximum (fwhm = 52 nm), which was even much better than that of commercially available BAM:Eu 2+ phosphor (color purity = 91.34%, fwhm = 51.7 nm). More importantly, the as-prepared BAO:Eu 2+ 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:Eu 2+ 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:Eu 2+ , it is a promising blue-emitting phosphor for n-UV WLED. ■ INTRODUCTIONRecently, phosphor-converted white light-emitting diodes (pc-WLEDs) lighting has been widely integrated into our daily lives

Bismuth ion is an excellent activator and sensitizer for luminescent materials, which has been extensively studied during the recent decades. Bi3+‐doped phosphors have received considerable attention for their abundant emission colors covering the whole visible light region under ultraviolet (UV) and near ultraviolet (n‐UV) excitation, in flexible crystal structures. These phosphor materials have demonstrated potential applications in solid‐state lighting, display, biomedical, and optical sensing. Herein, the recent advances in the structure design and photoluminescence properties of Bi3+‐doped phosphors together with their white light emitting diode (WLED) applications are reviewed. The design strategies for crystal structure and the discovery of typical phosphors are systematically summarized, and the luminescent properties of Bi3+ can be effectively regulated by these strategies. Then, the design of polychromatic Bi3+‐doped phosphors produced by different doping ions is described, which in turn can adjust the emission colors and realize a single‐component white‐light emission. This review will promote researches on the discovery of new Bi3+‐doped phosphor materials, and the design strategies could provide an extensive guidance for the discovery and preparation of high‐efficient phosphors with color‐tunable emission including white‐emission for WLEDs in the future. Additionally, research progress of Bi3+‐doped perovskite and Bi2+‐doped phosphor materials is briefly elucidated.

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.

Near‐infrared (NIR)‐emitting phosphor materials have been extensively developed for optoelectronic and biomedical applications. Although Cr3+‐activated phosphors have been widely reported, it is challenging to achieve ultra‐broad and tunable NIR emission. Here, a new ultra‐broadband NIR‐emitting LiIn2SbO6:Cr3+ phosphor with emission peak at 965 nm and a full‐width at half maximum of 217 nm is reported. Controllable emission tuning from 965 to 892 nm is achieved by chemical unit cosubstitution of [Zn2+–Zn2+] for [Li+–In3+], which can be ascribed to the upshift of 4T2g energy level due to the strengthened crystal field. Moreover, the emission is greatly enhanced, and the FWHM reaches 235 nm. The as‐prepared luminescent tunable NIR‐emitting phosphors have demonstrated the potential in night‐vision and NIR spectroscopy techniques. This work proves the feasibility of chemical unit cosubstitution strategy in emission tuning of Cr3+‐doped phosphors, which can stimulate further studies on the emission‐tunable NIR‐emitting phosphor materials.

Phosphor-converted white-light-emitting diodes (pc-WLED) have been extensively employed as solid-state lighting sources, which have a very important role in people’s daily lives. However, due to the scarcity of the red component, it is difficult to realize warm white light efficiently. Hence, red-emitting phosphors are urgently required for improving the illumination quality. In this work, we develop a novel orangish-red La4GeO8:Bi3+ phosphor, the emission peak of which is located at 600 nm under near-ultraviolet (n-UV) light excitation. The full width at half maximum (fwhm) is 103 nm, the internal quantum efficiency (IQE) exceeds 88%, and the external quantum efficiency (EQE) is 69%. According to Rietveld refinement analysis and density functional theory (DFT) calculations, Bi3+ ions randomly occupy all La sites in orthorhombic La4GeO8. Importantly, the oxygen-vacancy-induced electronic localization around the Bi3+ ions is the main reason for the highly efficient orangish-red luminescence. These results provide a new perspective and insight from the local electron structure for designing inorganic phosphor materials that realize the unique luminescence performance of Bi3+ ions.

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.

Upconversion nanoparticles (UCNPs) and MnO 2 hybrid theranostic nanoplatform (UCMn) is highly desired; however, the rational design of such UCMn hybrid nanomaterials is still a great challenge. Herein, a simple and versatile strategy for the in situ growth of MnO 2 on the surfaces of UCNPs was reported using a sacrificial template method to construct an ideal MnO 2 -disguised and tumor microenvironment−triggered architecture. Such sophisticated architecture not only achieves activatable magnetic resonance imaging and restorable upconversion luminescence (UCL) imaging with over 100-fold enhancement of UCL in vivo but also significantly improves the efficiency of chemodynamic therapy (CDT) by glutathione depletion-and cisplatinactivation-enhanced • OH generation simultaneously. Additionally, the synergetic effect of CDT and chemotherapy presents excellent therapeutic effect in vivo as compared to either CDT or chemotherapy alone. We believe that the ideal design of the MnO 2 -disguised upconversion hybrid nanocomposite will provide more revelations on the future research on nanoscale theranostic systems.

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.