Department of Physics, Banaras Hindu University, Varanasi, 221005, India.
Dalton Trans. 2011 Aug 7;40(29):7595-601. doi: 10.1039/c1dt10878f. Epub 2011 Jun 22.
When Eu(3+) ions occupy Ca(2+) sites of CaMoO(4), which has a body centered tetragonal structure with inversion symmetry, only the magnetic dipole transition ((5)D(0)→(7)F(1)) should be allowed according to Judd-Ofelt theory. Even if there are a few distortions in the Eu(3+) environment, its intensity should be more than that of the electric dipole transition ((5)D(0)→(7)F(2)). We report here the opposite effect experimentally and ascribe this to the polarizability effect of the MoO(4) tetrahedron, which is neighboring to EuO(8) (symmetric environment). The contribution of the energy transfer process from the Mo-O charge transfer band to Eu(3+) and the role of Eu(3+) over the surface of the particle could be distinguished when luminescence decay processes were measured at two different excitations (250 and 398 nm). Further, the luminescence intensities and lifetimes increase significantly with increasing heat-treatment temperature of the doped samples. This is attributed to the reduction of H(2)O from the surface of the particles and a non-radiative process after heat treatment.
当 Eu(3+) 离子占据 CaMoO(4)中的 Ca(2+)位时，由于 CaMoO(4)具有反演对称的体心四方结构，根据 Judd-Ofelt 理论，仅允许磁偶极跃迁((5)D(0)→(7)F(1))。即使 Eu(3+)环境有一些变形，其强度也应该超过电偶极跃迁((5)D(0)→(7)F(2))。我们在这里实验上报告了相反的效应，并将其归因于 MoO(4)四面体的极化率效应，该四面体与 EuO(8)相邻(对称环境)。当在两个不同的激发波长(250nm 和 398nm)下测量发光衰减过程时，可以区分从 Mo-O 电荷转移带向 Eu(3+)的能量转移过程的贡献以及 Eu(3+)在颗粒表面的作用。此外，掺杂样品的热处理温度升高时，发光强度和寿命显著增加。这归因于颗粒表面的 H(2)O 的减少和热处理后的非辐射过程。
