Ke Xing

Bio: Ke Xing is an academic researcher from Guangxi University. The author has contributed to research in topics: Full width at half maximum & Phosphor. The author has an hindex of 1, co-authored 3 publications receiving 3 citations.

Thermal and photo stability of all inorganic lead halide perovskite nanocrystals.

Abstract: Inorganic lead halide perovskite (ILHP) nanocrystals (NCs) show great potential in solid state lighting and next generation display technology due to their excellent optical properties. However, almost all ILHP NCs are still facing the problem of unstable luminescence properties caused by heating and/or UV illumination. Further improving the thermal and photo stability of ILHP NCs has become the most urgent challenge for their practical application. This Perspective review specifically focuses on the thermal and photo stability of ILHP NCs, discusses and analyzes the factors that affect the thermal and photo stability of ILHP NCs from the perspective of surface ligands and structure composition, summarizes the current strategies to improve the thermal and photo stability of ILHP NCs, and presents the key challenges and perspectives on the research for the improvement of thermal and photo stability of ILHP NCs.

Mg 2+-Assisted Passivation of Defects in CsPbI 3 Perovskite Nanocrystals for High-Efficiency Photoluminescence

Abstract: CsPbI3 perovskite nanocrystals (NCs) are emerging as promising materials for optoelectronic devices because of their superior optical properties. However, the poor stability of CsPbI3 NCs has become a huge bottleneck for practical applications. Herein, we report an effective strategy of Mg2+-assisted passivation of surface defects to obtain high emission efficiency and stability in CsPbI3 NCs. It is found that the introduced Mg2+ ions are mainly distributed on the surface of NCs and then passivate the NC defects, enhancing radiative decay rate and reducing nonradiative decay rate. As a result, the as-prepared Mg2+-treated CsPbI3 (Mg-CsPbI3) NCs exhibit the highest photoluminescence quantum yield (PLQY) of 95%. The Mg-CsPbI3 NC colloidal solution retains 80% of its original PLQY after 80 days of atmosphere exposure. The red perovskite light-emitting diodes based on the Mg-CsPbI3 NCs demonstrate an external quantum efficiency of 8.4%, which shows an almost 4-fold improvement compared to the devices based on the untreated NCs.

Advances in Chromium‐Activated Phosphors for Near‐Infrared Light Sources

Abstract: Cr3+/Cr4+‐activated near‐infrared (NIR) luminescent materials have attracted extensive attention owing to their tunable emission wavelength and widespread applications in plant growth, food analysis, biomedical imaging, night vision, and so on. Plenty of excellent NIR materials are developed by introducing Cr3+/Cr4+ ion to various inorganic hosts. Herein, the effect of crystal field on Cr3+/Cr4+ luminescence by combining the Tanabe–Sugano energy level diagram and configuration coordinate model is discussed. Research progress of Cr3+/Cr4+‐doped NIR luminescent materials, including the phosphors designed from structural models with octahedral, tetrahedral, and other coordination types, is then outlined. The luminescence properties of more than 200 kinds of Cr3+/Cr4+‐doped materials are summarized. In particular, several strategies for tuning emission wavelength, broadening emission band, enhancing NIR luminescence efficiency, and improving thermal stability, are listed. Finally, the current challenges and future prospects in the research of Cr3+/Cr4+‐doped NIR luminescent materials are presented. This review will contribute to a deeper understanding of not only Cr3+/Cr4+ luminescence mechanism but also the current research progress of chromium‐doped luminescent materials, so as to develop more Cr3+/Cr4+‐activated NIR luminescent materials with better performance and explore more applications.

Recent Advances in Chromium‐Doped Near‐Infrared Luminescent Materials: Fundamentals, Optimization Strategies, and Applications

Abstract: Development of chromium‐doped luminescent materials is pertinent to many emerging applications, ranging from agriculture, food industry to noninvasive health monitoring. The fundamental importance of chromium‐activated luminescent materials in the field of optics and biomedicine makes the rapid development of novel materials and relevant applications. Herein, the recent advances on the luminescence principle and photoluminescence (PL) optimization for Cr3+‐activated luminescent materials together with their potential applications are reviewed. The different types of most recently developed Cr3+‐doped luminescent materials and the design principles are systematically summarized. The associations between crystal structure and near‐infrared (NIR) PL properties, as well as performance‐evaluating parameters are introduced with the examples of known NIR emitting phosphors, which will be helpful to explore future NIR luminescent materials. Based on crystal field control, site engineering, and electron–phonon coupling, several efficient strategies for optimizing luminescence performances including bandwidth, thermal stability, and quantum efficiency of Cr3+‐doped NIR luminescent materials are proposed. Then, potential applications in the fields of food analysis, night vision, information encryption, and optical sensors are surveyed. Finally, the challenges of promising Cr3+‐doped luminescent materials are proposed.

Interstitial Li+ Occupancy Enabling Radiative/Nonradiative Transition Control toward Highly Efficient Cr3+-Based Near-Infrared Luminescence.

Abstract: Highly efficient and stable broadband near-infrared (NIR) emission phosphors are crucial for the construction of next-generation smart lighting sources; however, the discovery of target phosphors remains a great challenge. Benefiting from the interstitial Li+ occupancy-induced relatively large distorted octahedral environment for Cr3+ and suppressed nonradiative relaxation of the emission centers, an NIR emission fluoride phosphor Na3GaF6:Cr3+,Li+ peaking at 758 nm with a high internal quantum efficiency of 95.8% and an external quantum efficiency of 38.3% is demonstrated. Moreover, it exhibits a good thermal stability (84.9%@150 °C of the integrated emission intensity at 25 °C) and excellent moisture resistance as well. A high-power light-emitting diode (LED) with a record watt-level NIR output (974.12 mW) and a photoelectric conversion efficiency of 20.9% is demonstrated by combining Na3GaF6:Cr3+,Li+ and a blue InGaN chip, and a special information encryption/decryption technology suitable for rapid and long-distance identification of machines is further presented based on this device. This study not only advances the development of efficient NIR emission phosphors for broadband NIR LEDs but also for NIR-related emerging applications and devices.

Phase-Stable and Highly Luminescent CsPbI3 Perovskite Nanocrystals with Suppressed Photoluminescence Blinking.

Abstract: Despite their low band gap, the utility of CsPbI3 nanocrystals (NCs) in solar photovoltaic and optoelectronic applications is rather limited because of their phase instability and photoluminescence (PL) intermittency. Herein we show that phase-pure, monodispersed, stable and highly luminescent CsPbI3 NCs can be obtained by tweaking the conventional hot-injection method employing NH4I as an additional precursor. Single-particle studies show a significant suppression of PL blinking. Among all NCs studied, 60% exhibit only high-intensity ON states with a narrow distribution of intensity. The remaining 40% of NCs exhibit a much wider distribution of PL intensity with a significant contribution of low-intensity OFF states. Excellent characteristics of these CsPbI3 NCs are shown to be the result of NH4+ replacing some surface Cs+ of an iodide-rich surface of the NCs. These phase-stable and highly luminescent CsPbI3 NCs with significantly suppressed PL blinking can be useful single-photon emitters and promising materials for optoelectronic and solar photovoltaic applications.