Journal of the Chinese Ceramic Society, Volume. 52, Issue 5, 1739(2024)

Research Progress on Ni2+-Activated Ultra-Broadband Near-Infrared Emission Glass-Ceramics

GAO Zhigang1... ZHAO Rui1, XIAO Jing1,*, CUI Lugui2, WANG Ci2, QIAN Sen3 and REN Jing2 |Show fewer author(s)
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    Transition metal nickel ions (Ni2+) situated in a six-coordinate octahedral crystal field exhibit a ultra-broad near-infrared (NIR) luminescence, with a fluorescence half width at half maximum (HWHM) 6-8 times that of rare-earth (RE) element ions like Pr3+ and Er3+. Ni2+-activated NIR gain materials can be used in broadband optical amplifiers and tunable lasers, which have attracted attention. Despite their impressive luminescent efficiency, Ni2+-doped crystals have some limitations in optical fiber amplifier and laser applications due to their intricate fabrication processes, machining, and fiber formation. Glass offers some advantages in processing and fiber formation, but lacks a conducive crystal field (coordination field) environment for Ni2+ to achieve an efficient NIR luminescence. Various types of nanocrystals can be generated in-situ within the glass via subjecting glass to heat treatment, resulting in the formation of nanocrystalline composite glass-ceramics (GCs). Also, a precise control of grain size within the glass to dimensions smaller than the visible light wavelength (e.g., less than 30 nm) effectively mitigates the Rayleigh scattering, endowing GCs with reduced optical losses that meet the practical demands of photonic devices. Johnson, et al. investigated the optical properties of Ni2+. They prepared MgF2 crystals doped with Ni2+ and observed fluorescence emission characteristics and optical laser oscillation phenomena under pulse xenon lamp or tungsten lamp excitation at low temperatures (i.e., 20, 77 K, and 85 K). Ohishi et al. reported Ni2+ activated LiGa5O8 nanocrystalline GCs with a broadband fluorescence emission centered at 1.3 μm with a half-width greater than 300 nm under 976 nm excitation. The lifetimes at 5 k and 300 k were greater than 900 μs and 500 μs, respectively, with internal and external quantum efficiencies of 100% and 9%, respectively. This emission was attributed to the transition of Ni2+ from 3T2g(3F)→3A2g(3F) level in the LiGa5O8 crystal octahedral coordination. Zhou et al. reported the phenomenon of NIR light amplification in Ni2+ doped β-Ga2O3 nanocrystalline transparent GCs. Zhou et al. designed a special glass system with the composition of SiO2/Na2O/Ga2O3/LaF3 = 51%/15%/20%/14% (in mole). This glass system can orderly precipitate LaF3 and Ga2O3 nanocrystals. For co-doping with Er3+ and Ni2+, the two active ions can enter the two different nanocrystals, respectively, the physical distance between the two active ions and the local crystal field changes effectively inhibit the energy transfer between the two different active ions, achieving the near-infrared ultra-wideband luminescence of an integrated multi-color visible and Er3+/Ni2+ composite.Summary and prospects The existing fluorescence regulation of Ni2+-doped GCs is studied , having a great potential in broadband amplifiers, tunable lasers, non-invasive sensing, infrared night vision sources, and infrared medical diagnosis. Numerous studies indicate that 1) the NIR emission band and bandwidth of Ni2+ can be regulated via controlling the types (oxides, fluorides) and modes (single phase or dual phase) of crystals in GCs; 2) the luminescence intensity of Ni2+ can be further enhanced by energy transfer through sensitizers such as Nd3+, Yb3+, Cr3+, etc..; 3) the luminescence intensity of Ni2+ can be also enhanced by optical field regulation, such as using noble metal nanocrystals to improve the collection efficiency of pump light.However, Ni2+-activated transparent GCs still have some challenges. The doping concentration of Ni2+ in microcrystalline glass and microcrystalline glass fibers is relatively low, usually less than 0.2% (in mole fraction), resulting in low NIR absorption coefficients; The matrix glasses that can carry Ni2+ activation are still limited. Exploring multi-component glass matrices that can precipitate new types of crystal phases is one of the main tasks; Residual Ni2+ at the glass phase or glass-crystal phase interface still accounts for a large proportion. Some strategies are needed to ensure that most Ni2+ enters the target crystals, further improving its infrared optical performance; The gain coefficient of Ni2+-doped microcrystalline glass/fiber is relatively low (<0.3 cm-1) due to the limited volume ratio of nanocrystals in the glass (i.e., crystallization rate) and the influence of surface/interface defects of nanocrystals. Meanwhile, efficient positive feedback cannot be formed due to the lack of high-quality resonant cavities, resulting in only room-temperature luminescence of Ni2+, and no laser emission is achieved yet. The prerequisite for achieving laser emission is to obtain laser materials with sufficient gain.The Purcell effect can accelerate the radiation relaxation process of luminescent materials, resulting in an increased radiation probability and a correspondingly increased quantum efficiency of photoluminescence. Based on whispering gallery mode (WGM) glass microspheres, light can be confined in the micron-scale cavity for a long time based on the principle of total reflection. Therefore, it has an extremely high quality factor (i.e., ≥105) and minimal mode volume (i.e., ≤103 μm3), which can fully utilize the Purcell effect to enhance the interaction between light and matter. With the unique advantages of the WGM glass microsphere cavity, the preparation of a new Ni2+-doped microcrystalline glass microsphere laser provides an effective way to break through the physical bottleneck of room-temperature Ni2+ laser emission and develop low-threshold, ultra-broadband near-infrared multi-wavelength micro-lasers.

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    GAO Zhigang, ZHAO Rui, XIAO Jing, CUI Lugui, WANG Ci, QIAN Sen, REN Jing. Research Progress on Ni2+-Activated Ultra-Broadband Near-Infrared Emission Glass-Ceramics[J]. Journal of the Chinese Ceramic Society, 2024, 52(5): 1739

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    Paper Information

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    Received: Sep. 9, 2023

    Accepted: --

    Published Online: Aug. 20, 2024

    The Author Email: XIAO Jing (xiaojingzx@163.com)

    DOI:10.14062/j.issn.0454-5648.20230704

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