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首页> 外文期刊>RSC Advances >Why host to dopant energy transfer is absent in the MgAl2O4:Eu3+ spinel? And exploring Eu3+ site distribution and local symmetry through its photoluminescence: interplay of experiment and theory
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Why host to dopant energy transfer is absent in the MgAl2O4:Eu3+ spinel? And exploring Eu3+ site distribution and local symmetry through its photoluminescence: interplay of experiment and theory

机译：为什么MgAl2O4中缺乏掺杂剂能量转移：EU3 +尖晶石？通过光致发光探索EU3 +网站分布和局部对称性：实验与理论的相互作用

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An undoped and Eu ~(3+) doped magnesium aluminate spinel (MAS) was synthesized using a citric acid assisted combustion technique. MAS samples were characterized systematically using X-ray diffraction (XRD), time resolved photoluminescence spectroscopy (TRPLS) and ab initio calculations. On irradiating the undoped MAS with UV light; multicolor emission is observed. The blue emission peak was attributed to Mg ~(2+) vacancies whereas the one in the green region was attributed to oxygen vacancies. Based on the emission spectrum it was inferred that the majority of europium ions are localized at the Mg ~(2+) site which was also confirmed using lifetime measurements. DFT based cohesive energy calculations also showed Eu doping in the Mg position is energetically more favorable than doping in the Al position. Photoluminescence (PL) spectroscopy shows that the emission spectrum consists of host as well as Eu ~(3+) emission indicating the absence of complete host–dopant energy transfer. DFT calculated density of states analysis shows that Eu states are solely localized in VB and CB regions and do not contribute in defects states. From the emission spectrum of the undoped MAS sample it was observed that photo-luminescence properties of the MgAl _(2) O _(4) are dominantly governed by the defect states coming from the presence of cation and oxygen vacancies (neutral and charged). As a result photon energy transfer from host MAS to dopant Eu is difficult. The actual site symmetry for europium ions in MAS was also evaluated based on a stark splitting pattern which comes out to be C _(2v) . Based on Judd–Ofelt analysis it was found that the Ω _(2) value is greater than Ω _(4) ; indicating high covalency and low symmetry around europium ions which is also observed in the emission spectrum. The high purity of the red emission coupled with good fluorescence quantum yields highlights the potential of this unexplored MAS as a promising phosphor.
机译：使用柠檬酸辅助燃烧技术合成未掺杂的和EU〜（3+）掺杂的铝铝酸镁型尖晶石（MAS）。使用X射线衍射（XRD），时间分辨的光致发光光谱（TRPL）和AB Initio计算，系统地表征了MAS样本。用UV光照射未掺杂的MAS;观察到多色发射。蓝色发射峰值归因于Mg〜（2+）职位空缺，而绿色区域中的那个归因于氧空位。基于发射光谱，推断大部分铕离子在Mg〜（2+）位点上局部化，也使用寿命测量确认。基于DFT基的粘性能量计算还显示EU掺杂在MG位置比掺杂在Al位置的掺杂能量更强。光致发光（PL）光谱表明，发射光谱由主机以及Eu〜（3+）发射组成，表明没有完全宿主掺杂能量转移。 DFT计算的状态分析密度表明，欧盟各州仅在VB和CB地区本地化，并且在缺陷状态下没有贡献。从未掺杂的MAS样品的发射光谱观察到MGAL _（2）O _（4）的光发光特性由来自存在阳离子和氧空位（中性和充电）的缺陷状态占主导地位。结果，从主体MAS到掺杂剂EU的光子能量转移是困难的。还基于STARK分裂模式评估了MAS中铕离子的实际站点对称性，这是C _（2V）。基于Judd-ofelt分析，发现ω_（2）值大于ω_（4）;表示在发射光谱中也观察到的高共和度和低对称性，其在发射光谱中观察到。具有良好荧光量子产量的红色发射的高纯度突出了这种未探测的MAS作为有前途的磷光体的潜力。

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