High-brightness red-emitting double-perovskite phosphor Sr2LaTaO6:Eu3+ with high color purity and thermal stability
Emission spectrum and CIE chromaticity coordinates of the as-prepared Sr2LaTaO6:0.2Eu3+ red phosphors.
At present, the environmental problems such as resource depletion, water pollution and air pollution caused by the development of nature resources have are raised great social concerns. Among the environmental issues, lighting electricity accounts for about 20% of global electricity consumption. Compared with traditional lighting sources such as incandescent lamps and fluorescent lamps, white light emitting diodes (LEDs) have many outstanding advantages like high energy efficiency, long working life, environmental friendliness, and etc. Therefore, the development of LEDs lighting is an effective solution to save power and protect the global environment.
Nowadays, the widely used white LEDs are commonly manufactured by combining InGaN blue LEDs chips with Y3Al5O12:Ce3+ yellow-emitting phosphors. However, due to lack of red light, there are some limitations in these white LEDs, including high correlated color temperature and low color rendering index. Instead, the near-ultraviolet (near-UV) pumped white LEDs based on the combination of near-UV LED chips and tri-color (blue, green, and red) phosphors can exhibit warm white light with high color rendering index. Yet, there is still a lack of red phosphors excited by near-UV light with good performance for white LEDs. Thus, research on near-UV-light-excitable red phosphor is of great importance to both practical application and scientific research. It is well-known that Eu3+ ion is an excellent activator for inorganic phosphors because of its bright red emissions due to the 5D0→7FJ (J = 1, 2, 3, 4) transitions. The optical properties of Eu3+ ions are critically influenced by the used host materials. In recent years, the double-perovskite compounds with molecular formula of A2BMO6 have been widely selected as outstanding host materials for Eu3+ ions.
A research group led by Prof. Xiaoyong Huang from Taiyuan University of Technology discovered a novel bright red-emitting Eu3+ ions doped Sr2LaTaO6 double-perovskite phosphor. The related results are published in Chinese Optics Letters, Volume 19, Issue 3, 2021 (Z. Zhang, et al., High-brightness red-emitting double-perovskite phosphor Sr2LaTaO6:Eu3+ with high color purity and thermal stability). A series of Sr2LaTaO6:Eu3+ phosphors doped with different Eu3+ concentrations were prepared by using a high-temperature solid-state reaction method. Impressively, the obtained Sr2LaTaO6:Eu3+ phosphor exhibited intense absorption in the near-UV wavelength range peaking at 394 nm, thus this phosphor could be used in near-UV-pumped white LEDs. Moreover, under 394 nm excitation, the Sr2LaTaO6:Eu3+ phosphor can emit bright red light around 613 nm. The optimal doping concentration of Eu3+ ions was found to be 20 mol%, and the integrated emission intensity of Sr2LaTaO6:0.2Eu3+ phosphor was about three times higher than that of commercial Y2O2S:Eu3+ red phosphor. Furthermore, the CIE chromaticity coordinates of Sr2LaTaO6:0.2Eu3+ phosphors were measured as (0.650, 0.349), which were close to that of ideal red light (0.67, 0.33). The color purity can reach about 92%. In addition, these Sr2LaTaO6:0.2Eu3+ red phosphors show good thermal stability.
The experimental results not only showed that these novel red-emitting phosphors have great potential as a red phosphor for near-UV-pumped white LEDs but also verified that the double-perovskite compound can be a good host for Eu3+ luminescent materials. The research team will further investigate on Eu3+ doped double-perovskite phosphors to obtain luminescent materials with better performances in the near future.
遗憾的是，目前无论工业或研究领域仍然缺少性能良好的可被近紫外光激发的LED用红色荧光粉，相关研究具有巨大的实际应用和科研价值。众所周知，Eu3+离子是无机荧光粉常用的发光离子，这是由于其5D0→7FJ（J = 1, 2, 3, 4）跃迁可以发出明亮的红光。Eu3+离子的光学性能很大程度上受其所用基质材料的影响。近年来，分子式为 A2BMO6的双钙钛矿化合物已被广泛选作Eu3+离子的良好基质材料。
太原理工大学黄小勇教授领导的研究小组首次发现了一种新型高效的Eu3+离子掺杂Sr2LaTaO6双钙钛矿红色荧光粉。相关结果发表在Chinese Optics Letters第19卷第3期（Z. Zhang et al., High-brightness red-emitting double-perovskite phosphor Sr2LaTaO6:Eu3+ with high color purity and thermal stability [Invited]）。该研究小组采用高温固相法成功制备了一系列掺杂不同Eu3+浓度的Sr2LaTaO6:Eu3+红色荧光粉。
研究发现，Sr2LaTaO6:Eu3+荧光粉在峰值为394 nm的近紫外波长范围内表现出强烈的吸收，因此该荧光粉可用于近紫外激发的白色LED器件。并且，在394 nm激发下，Sr2LaTaO6:Eu3+荧光粉可发出波长为613 nm左右的明亮红光。研究还发现Eu3+离子的最佳掺杂浓度为20 mol％，同时Sr2LaTaO6:0.2Eu3+红色荧光粉的发光积分强度约为商业Y2O2S:Eu3+红色荧光粉的3倍。此外，Sr2LaTaO6:0.2Eu3+荧光粉的CIE色坐标为（0.650，0.349），接近理想红光的CIE色坐标（0.67，0.33），其色纯度可以达到约92％。同时，这些Sr2LaTaO6:0.2Eu3+红色荧光粉表现出良好的热稳定性。