Nucleation sequence on the cation exchange process between Y_(0.95)Eu_(0.05)PO4 and CePO4 nanorods

摘要

Nanorods of Y_(0.95)Eu_(0.05)PO4@CePO4 (Y_(0.95)Eu_(0.05)PO4 phase was nucleated first and then a CePO4 phase was nucleated) and CePO4@Y_(0.95)Eu_(0.05)PO4 (CePO4 phase was nucleated first and then Y_(0.95)Eu_(0.05)PO4 phase was nucleated) were prepared at a relatively low temperature of 140 °C in ethylene glycol medium. Based on XRD, TEM and Raman studies it has been inferred that Y_(0.95)Eu_(0.05)PO4@CePO4 sample consists of a mixture of bigger (length around 800-1000 nm and width around of 80-100 nm) and smaller (length around 70-100 nm and width around 10-20 nm) nanorods, having monoclinic CePO4 and tetragonal YPO4 structure, whereas CePO4@Y_(0.95)Eu_(0.05)PO4 sample consists of mainly small nanorods having a single phase CePO4 structure. From the detailed luminescence studies it has been established that there exists significant incorporation of Y~(3+)/Eu~(3+) ions in the CePO4 phase in CePO4@Y_(0.95)Eu_(0.5)PO4 sample. This has been attributed to the cation exchange taking place between Ce~(3+) ions in CePO4 host and Eu~(3+) and Y~(3+) ions in solution during the synthesis stage. Unlike this, such an exchange is not possible for Y_(0.95)Eu_(0.05)PO4@CePO4 sample synthesized under identical conditions due to the higher solubility product (K_(sp)) value of YPO4 compared to CePO4. Incorporation of Eu~(3+) in the CePO4 lattice of CePO4@Y_(0.95)Eu_(0.5)PO4 sample is confirmed by the significant reduction in the lifetime of ~5D0 level of Eu~(3+) and the luminescence intensity from Eu~(3+), arising due to the electron transfer between the Ce~(3+)/Ce~(4+) and Eu~(3+)/Eu~(2+) species. These results are further supported by the non-radiative decay rates and quantum yields calculated from the emission spectrum.