Organic light-emitting diodes (OLEDs) have had commercial success in displays and lighting. Compared to red and green OLEDs, blue OLEDs are still the bottleneck because the high-energy and long-lived triplet exciton in traditional blue OLEDs causes the short operational lifetime of the device. As a new type emitter, lanthanide complexes with a 5d–4f transition could have short excited-state lifetimes on the order of nanoseconds. To achieve a high-efficiency 5d–4f transition, we systematically tuned the steric and electronic effects of tripodal tris(pyrazolyl)borate ligands and drew a full picture of their Ce(III) complexes. Intriguingly, all of these complexes show bright blue emission with high photoluminescence quantum yields exceeding 95% and short decay lifetimes of 35–73 ns both in the solid powder and in dichloromethane solutions. Using the Ce(III) complex emitter, we show a blue OLED with a maximum external quantum efficiency of 14.1% and a maximum luminance of 33,160 cd m^–2, and the specific electroluminescence mechanism of direct exciton formation on the Ce(III) ion with a near-unity exciton utilization efficiency is also confirmed. The discovered photoluminescence and electroluminescence property–structure relationships may shed new light on the rational design of highly efficient lanthanide-based blue emitters and their optoelectronic devices such as OLEDs.

中文翻译：

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镧系元素铈（III）三（吡唑基）硼酸盐配合物：双线态有机发光二极管的高效蓝色发射体

有机发光二极管 (OLED) 在显示器和照明领域取得了商业成功。与红色和绿色 OLED 相比，蓝色 OLED 仍然是瓶颈，因为传统蓝色 OLED 中高能量和长寿命的三线态激子导致器件的使用寿命较短。作为一种新型发射体，具有 5d-4f 跃迁的镧系元素配合物可能具有纳秒量级的短激发态寿命。为了实现高效的 5d-4f 跃迁，我们系统地调整了三足三（吡唑基）硼酸盐配体的空间和电子效应，并绘制了它们的 Ce（III）配合物的全貌。有趣的是，所有这些复合物在固体粉末和二氯甲烷溶液中都显示出亮蓝色发射，光致发光量子产率超过 95%，衰变寿命短，均为 35-73 ns。^–2，并且还证实了具有接近统一的激子利用效率的 Ce(III) 离子直接激子形成的特定电致发光机制。发现的光致发光和电致发光特性-结构关系可能为高效镧系元素蓝色发射器及其光电器件（如 OLED）的合理设计提供新的思路。