K2TiF4:Mn4+ Red Phosphor and High-Efficiency Warm White LED Device Synthesized by Wet Chemical Method White LEDs are the next generation of lighting devices because of their energy-saving, environmental-friendly and long-life characteristics. Currently, commercially available white LEDs mainly use a blue chip to excite YAG:Ce3+ yellow phosphor. The blue light emitted from the chip is mixed with the yellow light emitted by the phosphor to form white light. However, the emission spectrum of YAG:Ce3+ phosphor has insufficient red light component, so it is difficult to obtain a low correlated color temperature (CCT<4500K) and a high color rendering index (CRI) with a single YAG:Ce3+ phosphor. The warm white light device of 80) has led to its limitations in the application of indoor general lighting. In order to solve this problem, it is necessary to add a suitable red phosphor in the device to supplement the red component to prepare a warm white LED device with a low color temperature and a high color rendering index. At present, commercially available red phosphors with good performance are mainly rare earth-doped nitrogen (oxygen) materials. However, such phosphors have disadvantages such as excessive emission bandwidth and severe preparation process, resulting in low lumen efficiency. expensive. Therefore, the development of low-cost, narrow-band emission red phosphors that can be effectively excited by blue chips has become a focus of attention especially for replacing rare-earth light-emitting materials, which is also the key to improving the lumen efficiency of warm-white LEDs. Under the support of the National Youth Foundation for Distinguished Young Scientists Fund and the Joint Fund for Promoting Cross-Strait Science and Technology Cooperation, the Innovation International Team of the Chinese Academy of Sciences, and major special projects of Fujian Province, the Chen Xueyuan Research Group of Fujian Institute of Materials Structure of the Chinese Academy of Sciences cooperated with the research team of Liu Ruyi of Taiwan University for the first time. Mn4+-doped K2TiF6, K2SiF6, NaYF4, and NaGdF4 red phosphors were successfully prepared using a high-performance ion exchange method. These phosphors have a strong absorption band (bandwidth ~50 nm) at ~460 nm, which is suitable for the excitation of blue chips. Its emission is a sharp-line red emission of ~630 nm, which has a higher radiation lumen efficiency than the nitrogen (oxygen) red phosphor. In particular, K2TiF6:Mn4+ phosphor has an absolute quantum yield of 98% at room temperature, which is superior to most of the existing red phosphors; at the same time, the phosphor has excellent fluorescence thermal stability at 150°C. The luminous intensity reaches 98% at room temperature; the warm white LED device packaged with the combination of the red phosphor and the YAG:Ce3+ yellow phosphor has a color temperature of 3556K, a color rendering index of 81, and a lumen efficiency of 116 lm/W at a driving current of 60 mA. . The ion exchange preparation method developed by the research team has a simple process, can be prepared at room temperature and atmospheric pressure, and the raw materials are cheap, so it has a good market application prospects. In addition, the research team also conducted in-depth study of the spectral characteristics of Mn4+ ions in the fluoride matrix, revealing its electronic energy level structure through low-temperature, high-resolution laser spectroscopy, and explaining its anomalous luminous intensity-temperature dependence. These provide a theoretical basis for further research and development of such non-rare-earth red light emitting materials. The above work was published online in the full text on July 8th in Nature Communications 2014 (5,4312.DOI:10.1038/ncomms5312) and applied for two invention patents. Previously, Chen Xueyuan’s research group has made progress in the electronic structure and optical properties of inorganic phosphors (“China Science-Chemicalâ€, 2014, 44, 168, cover), and the three tasks were selected as important optical achievements of China in 2010, 2011, and 2013 respectively. 10 papers were selected for ESI high cited papers in the fields of chemistry, materials and physics in the past decade.
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