Deciphering crystal structure of Li <sub>3</sub> Bi <sub>3</sub> Te <sub>2</sub> O <sub>12</sub> :Sm <sup>3+</sup> phosphors with high thermal stability for plant cultivation and white light‐emitting diodes
Shigao Chen, Junzhi Che, Bin Zhao, Shulei Li, Xuemei Yao, Yue Yang, Ya Yang, Xiang Liu, Ruijin Yu
Abstract
Abstract The novel orange‐red light‐emitting garnet‐type phosphors Li 3 Bi 3 Te 2 O 12 : x Sm 3+ (0.005 ≤ x ≤ 0.25) were first synthesized using the high‐temperature solid‐state reaction method. The phase structure was recorded with XRD. Raman spectroscopic analysis was conducted for the first time to extract detailed structural insights of the tellurate garnet Li 3 Bi 3 Te 2 O 12 :Sm 3+ . The characteristics of the obtained compounds were investigated, including particle morphology, elemental mapping, diffuse reflection spectra, excitation and emission spectra, thermal stability, chromaticity coordinates according to the Commission International del′Eclairage, and color purity. The Li 3 Bi 3 Te 2 O 12 :Sm 3+ phosphor could be effectively excited by 406 nm irradiation, and four sharp peaks were presented. The dominant peaks are located at 613 and 653 nm, corresponding to the typical transition of Sm 3+ ions at 4 G 5/2 → 6 H 7/2 and 4 G 5/2 → 6 H 9/2 , respectively. The phosphors present a regular concentration quenching trend, with an optimum Sm 3+ doping concentration of 0.02. Impressively, the product demonstrates remarkable thermal stability by maintaining an emission intensity of 93% at a working temperature of 423 K. Additionally, the thermal quenching temperature ( T 0.5 ) surpasses 480 K. The lighting performance of the white light‐emitting diode fabricated using Li 3 Bi 3 Te 2 O 12 :0.02Sm 3+ phosphor has been found to be exceptional, characterized by a high color rendering index ( R a = 90) and a low correlated color temperature (CCT = 5122 K). The electroluminescent spectrum of the red light‐emitting diode device fabricated by Li 3 Bi 3 Te 2 O 12 :0.02Sm 3+ overlapped well with the absorption spectra of the phytochromes, suggesting its potential for plant cultivation light source. In conclusion, considering all these photoluminescent properties mentioned above, Li 3 Bi 3 Te 2 O 12 :Sm 3+ phosphor can be regarded as a promising material for daily illumination and plant cultivation LEDs.