Nakamura Hitomi, Shinozaki Kenji, Okumura Toyoki, Nomura Katsuhiro, Akai Tomoko
National Institute of Advanced Industrial Science and Technology (AIST) 1-8-31 Midorigaoka, Ikeda Osaka 563-8577 Japan
National Institute of Advanced Industrial Science and Technology (AIST) 2266-98 Anagahora Shimoshidami, Moriyama-ku Nagoya Aichi 463-8560 Japan.
RSC Adv. 2020 Mar 27;10(21):12535-12546. doi: 10.1039/d0ra01381a. eCollection 2020 Mar 24.
In light emitting diodes, YAlO:Ce (YAG:Ce) is used as a yellow phosphor in combination with blue LEDs but lacks a red component in emission. Therefore, considerable efforts have been directed toward shifting the emission of YAG:Ce to longer wavelengths. In this study, a YAlO (YAG) crystal incorporating a high content of Ce, (Y Ce )AlO (0.006 ≦ ≦ 0.21), was successfully prepared by a polymerized complex method in which low-temperature annealing (650-750 °C) was employed prior to sintering at 1080 °C. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis indicated that the obtained sample was a single phase YAG crystal with ≤ 0.21. Interestingly, orange-red emission was observed with ≥ 0.07 with UV-blue light irradiation. With excitation at 450 nm, the emission peak increases from 538 nm ( = 0.006) to 606 nm ( = 0.21). This massive red shift in the high- region was not observed without the 1 step of low-temperature annealing, which implied that low-temperature annealing was essential for incorporating a high concentration of Ce. The precursor formed by low-temperature annealing was amorphous at = 0.04, whereas CeO nanocrystals were formed in the amorphous material with ≥ 0.11, based on the XRD and TEM results. CeL X-ray absorption edge structure revealed that Ce existed as Ce in the precursor and Ce in the obtained crystal. It was speculated that CeO was formed at low temperature, releasing oxygen, with sintering at 1080 °C, leading to the incorporation of Y in the Ce-O framework. The lattice constant increased significantly from 12.024 Å to 12.105 Å with increasing , but the crystal field splitting did not increase and was constant from = 0.06 to = 0.21. Hence, the massive red shift in emission was not explained by the large crystal field splitting, but instead by the Stokes shift.
在发光二极管中，钇铝石榴石：铈（YAG：Ce）被用作黄色荧光粉与蓝色发光二极管结合使用，但发射光中缺少红色成分。因此，人们致力于将YAG：Ce的发射光波长移向更长波长。在本研究中，通过聚合络合法成功制备了一种掺入高含量铈的钇铝石榴石（YAG）晶体，即（Y1-xCex）3Al5O12（0.006 ≤ x ≤ 0.21），该方法在1080°C烧结之前采用了低温退火（650 - 750°C）。X射线衍射（XRD）和透射电子显微镜（TEM）分析表明，所得样品是x ≤ 0.21的单相YAG晶体。有趣的是，当x ≥ 0.07时，在紫外蓝光照射下观察到橙红色发射光。在450nm激发下，发射峰从538nm（x = 0.006）增加到606nm（x = 0.21）。在没有低温退火步骤的情况下，在高x区域未观察到这种巨大的红移，这意味着低温退火对于掺入高浓度的铈至关重要。根据XRD和TEM结果，在x = 0.04时低温退火形成的前驱体是无定形的，而在x ≥ 0.11时，在无定形材料中形成了CeO纳米晶体。Ce L X射线吸收边结构表明，Ce在前驱体中以Ce3+形式存在，在所得晶体中以Ce4+形式存在。据推测，在低温下形成CeO，释放出氧气，在1080°C烧结时，导致Y掺入Ce - O骨架中。随着x的增加，晶格常数从12.024Å显著增加到12.105Å，但晶体场分裂没有增加，在x = 0.06到x = 0.21范围内保持恒定。因此，发射光的巨大红移不是由大的晶体场分裂解释的，而是由斯托克斯位移解释的。
