Tuning of Bi3+-related excitation and emission positions through crystal field modulation in the perovskite-structured La2(Znx, Mg1-x)TiO6 (0 ≤ x ≤ 1):Bi3+ solid solution for white LEDs |
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Authors: | Taiping Xie Li Zhang Ying Guo Xinxing Wang Yajing Wang |
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Affiliation: | 1. Chongqing Key Laboratory of Extraordinary Bond Engineering and Advanced Materials Technology (EBEAM), Yangtze Normal University, Chongqing 408100, PR China;2. Chongqing Academy of Metrology and Quality Inspection, Chongqing 401123, PR China;3. College of Chemistry and Life Science, Zhejiang Normal University, Hangzhou 310058, China;4. School of Chemistry and Chemical Engineering, Harbin Institute of Technology, 150001, China |
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Abstract: | In the past year, emission-tunable crystals based on the rare-earth (RE) ions as luminescent center have been frequently reported for use in UV and blue converted white LEDs, but so far tuning the non-RE Bi3+ related emissions through the crystal field modulation is still not discovered in the perovskite crystals. In this work, we design and report a type of Bi3+ doped La2(Znx,Mg1-x)TiO6 (0 ≤ x ≤ 1) perovskite solid solutions, which enable showing the tunable Bi3+ excitation and emission positions. The XRD results show that gradual substitution of smaller Mg2+ ions with larger Zn2+ ions can lead to the blue-shifting of X-ray diffraction (XRD) position, revealing the expansion of cell lattice. Together with structural analysis, our refined XRD and time-resolved spectral results reveal that there is only one type of La site available for Bi3+ substitution. With this regular crystal lattice change, the crystal field strength around Bi3+ ions is found to vary regularly, allowing to realization of the excitation and emission spectral tuning, i.e., the Bi3+ excitation and emission positions as the Mg ions are replaced by the Zn ions can tune from 348?nm to 392?nm and from 405?nm to 433?nm, respectively. This Bi3+ spectral tuning peak after calculated by the dielectric chemical bond theory features a linear relationship with the crystal field strength and, thus, is ascribed to the crystal field modulation. On basis of the La2(Zn0.4,Mg0.6)TiO6 blue, SrGa2S4:Eu2+ green and Y2O3:Eu3+ red phosphors, a UV converted warm white LED device with desirable color rendering index (CRI) of 78, correlated color temperature (CCT) of 3650 K and good luminous efficacy of 118.13?lm/W, is fabricated. This work provides new insights into using the crystal-field modulation to discover more Bi3+ emission-tunable crystals for white LEDs in the future. |
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Keywords: | Tunable emission Perovskite Crystal field modulation LEDs |
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