Spontaneous emission in the ellipsoidal nanocrystals

Importance of Volume Ratio in Photonic Effects of Lanthanide-Doped LaPO4 Nanocrystals

Experimental variation of the volume ratio (filling factor: i.e., volume of nanoparticles (NPs) compared with that of medium) of nanocomposite materials with doped lanthanide ions demonstrates that it has a significant affect upon local field effects. Lanthanum orthophosphate NPs are doped with Eu³⁺ and/or Tb³⁺ and immersed in organic solvents and lead borate glasses for Tb^{3+ 5} D₄ lifetime measurements. For media with a refractive index (n_med ) less than that of LaPO₄ (n_np = 1.79), the ⁵ D₄ emission decay rate increases with increasing volume ratio of the NPs, whereas for n_med > 1.79, the decay rate decreases with increasing volume ratio. Fitting with the model of Pukhov provides an estimation of the radiative lifetime of ⁵ D₄ and the quantum yield. Energy transfer (ET) from Tb³⁺ to Eu³⁺ occurs in co-doped LaPO₄ NPs with excitation into a Tb³⁺ absorption band. The ET rate is independent on n_med and the energy transfer efficiency decreases with an increase in n_med . The behavior of ET rate with regard to the local field is consistent with the Dexter, but not Förster, equation for ET rate involving the electric dipole-electric dipole mechanism. This has consequences when using the spectroscopic ruler approach to measure distances between donor-acceptor chromophores.