Luminescent properties of LaPO4:Eu nanoparticles and nanowires

Nanoparticles (NPs) and nanowires (NWs) as well as micrometer particles (MPs) and micrometer rods (MRs) of LaPO4:Eu phosphors were synthesized by the hydrothermal method. Their luminescent properties, including local symmetry surrounding Eu3+ ions and electronic transition processes, were studied and compared. The results indicated that, in NPs and MPs, Eu3+ occupied only one site, A, while in NWs and MRs, Eu3+ occupied the same site, A, and an additional site, B. Varying from NWs to MRs, the relative emission intensity of Eu3+ ions at site B was reduced. The radiative transition rates of D-5(1)-Sigma(J)(7)F(J) and nonradiative transition rates of D-5(1)-D-5(0) in different powders were obtained by measuring temperature-dependent luminescent dynamics. The results indicated that the radiative transition rate of D-5(1)-Sigma(J)(7)F(J) in NWs increased 1.5-1.8 times over that in NPs, MPs, and MRs, while the nonradiative transition rates had only a little variation. Thereby, the luminescent quantum efficiency (QE) of D-5(1) at 0 K in NPs, NWs, MPs, and MRs was deduced to be 38%, 59%, 49%, and 47%, respectively. The radiative transition rate of D-5(0)-Sigma(J)(7)F(J) in NWs also increased similar to1.5 times. The increase of the radiative electronic transition rate in NWs was attributed to the variation of dipole field caused by the shape anisotropy.