Desirable phosphors for lighting, scintillation and composite films must have good light absorption properties, high concentration quenching, high quantum efficiency, a narrow color emission, and so forth. In this work, we first show that undoped yttrium hafnate Y₂Hf₂O₇ (YHO) nanoparticles (NPs) display dual blue and red bands after excitation using 330 nm light. Based on density functional theory (DFT) calculations, these two emission bands are correlated with the defect states arising in the band-gap region of YHO owing to the presence of neutral and charged oxygen defects. Once doped with Eu³⁺ ions (YHOE), the YHO NPs show a bright red emission, a long excited state lifetime and stable color coordinates upon near-UV and X-ray excitation. Concentration quenching is active when Eu³⁺ doping reaches 10 mol% with a critical distance of ∼4.43 Å. This phenomenon indicates a high Eu³⁺ solubility within the YHO host and the absence of Eu³⁺ clusters. More importantly, the optical performance of the YHOE NPs has been further improved by lithium co-doping. The origin of the emission, structural stability, and role of Li⁺-co-doping are explored both experimentally and theoretically. DFT calculation results demonstrate that Li⁺-co-doping increases the covalent character of the Eu³⁺–O²⁻ bonding in the EuO₈ polyhedra. Furthermore, the YHOE NPs have been dispersed into polyvinyl alcohol (PVA) to make transparent nanocomposite films, which show strong red emission under excitation at 270 and 393 nm. Overall, we demonstrate that the YHO NPs with Eu³⁺ and (Eu³⁺/Li⁺) doping have a high emission intensity and quantum efficiency under UV and X-ray excitation, which makes them suitable for use as phosphors, scintillators and transparent films for lighting, imaging and detection applications.

中文翻译：

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未掺杂，Eu3 +掺杂和Li +共掺杂的Y2Hf2O7纳米粒子和聚合物纳米复合薄膜的光学性质

用于照明，闪烁和复合膜的理想磷光体必须具有良好的光吸收特性，高浓度猝灭，高量子效率，窄色发射等。在这项工作中，我们首先显示了未掺杂的钇酸钇Y ₂ Hf ₂ O ₇（YHO）纳米颗粒（NPs）在使用330 nm光激发后显示出蓝色和红色双谱带。基于密度泛函理论（DFT）计算，由于存在中性和带电的氧缺陷，这两个发射带与YHO带隙区域中出现的缺陷状态相关。一次掺杂Eu ³⁺离子（YHOE）时，YHO NP在近紫外和X射线激发下显示亮红色发射，长激发态寿命和稳定的色坐标。当Eu ³⁺掺杂达到10 mol％且临界距离约为4.43Å时，浓度猝灭才起作用。此现象表明YHO主体中Eu ^3+的溶解度较高，并且Eu ³⁺团簇不存在。更重要的是，通过共掺杂锂，YHOE NP的光学性能得到了进一步提高。通过实验和理论研究了发光的起源，结构稳定性以及Li ⁺ -共掺杂的作用。DFT计算结果表明，Li ⁺ -共掺杂提高了Eu ³⁺ -O的共价特性EuO ₈多面体中的²⁻键合。此外，已将YHOE NP分散到聚乙烯醇（PVA）中以制成透明的纳米复合膜，该膜在270和393 nm的激发下显示出强红色发射。总体而言，我们证明了掺有Eu ³⁺和（Eu ³⁺ / Li ⁺）的YHO NP在紫外和X射线激发下具有高发射强度和量子效率，这使其适合用作荧光粉，闪烁体和透明材料。用于照明，成像和检测应用的胶卷。