Gupta Santosh K, Sahu M, Ghosh P S, Tyagi Deepak, Saxena M K, Kadam R M
Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, India.
Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, India.
Dalton Trans. 2015 Nov 21;44(43):18957-69. doi: 10.1039/c5dt03280f.
Undoped and europium doped CaMoO4 and SrMoO4 scheelites are synthesized using a complex polymerization method. The phase purity of the sample is confirmed using powder X-ray diffraction (PXRD). X-ray photoelectron spectroscopy (XPS) was carried out to confirm the oxidation states of various constituents and dopant elements and also the presence of oxygen vacancies. Interestingly both CaMoO4 and SrMoO4 on irradiation with UV light give blue and green emission respectively. On europium doping, it was found that molybdate to Eu(3+) ion energy transfer is more efficient in SrMoO4:Eu compared to CaMoO4:Eu. It is also justified using a luminescence lifetime study which shows biexponential decay in the case of CaMoO4:Eu corresponding to both the host and europium ion; whereas a single lifetime is observed in the case of SrMoO4:Eu. Anomalies in host-dopant energy transfer are suitably explained using density functional theory (DFT) calculations and XPS. The actual site symmetry for the europium ion in CaMoO4 and SrMoO4 was also evaluated based on a Stark splitting pattern which turns out to be D2 and C2v respectively although it is S4 for Ca/Ba(2+) in AMoO4. This is also reflected in higher Ω2 values for SrMoO4:Eu than CaMoO4:Eu.
采用络合聚合法合成了未掺杂和铕掺杂的钼酸钙（CaMoO4）和钼酸锶（SrMoO4）白钨矿。使用粉末X射线衍射（PXRD）确认样品的相纯度。进行X射线光电子能谱（XPS）以确认各种成分和掺杂元素的氧化态以及氧空位的存在。有趣的是，CaMoO4和SrMoO4在紫外光照射下分别发出蓝色和绿色光。在铕掺杂时，发现与CaMoO4:Eu相比，SrMoO4:Eu中钼酸盐到Eu(3+)离子的能量转移更有效。这也通过发光寿命研究得到了证实，该研究表明CaMoO4:Eu中对应于主体和铕离子的双指数衰减；而在SrMoO4:Eu中观察到单一寿命。使用密度泛函理论（DFT）计算和XPS对主体-掺杂剂能量转移中的异常现象进行了适当解释。基于斯塔克分裂模式还评估了CaMoO4和SrMoO4中铕离子的实际位点对称性，结果分别为D2和C2v，尽管对于AMoO4中的Ca/Ba(2+)是S4。这也反映在SrMoO4:Eu的Ω2值高于CaMoO4:Eu。
