RESUMEN
The radiative lifetime of an emitter (such as a luminescent ion) is affected not only by the properties of the emitter itself but also by the dielectric properties of the surrounding media. The fluctuation of the local electrical field caused by random distribution of polarized luminescent-ion-containing nanoparticles in media leads to the fluctuation of radiative lifetime of luminescent ions. Lifetime fluctuation has been calculated analytically by considering this effect. The results show that the fluctuation of radiative lifetime is not negligible and can be shown and observed in future experiments.
RESUMEN
The structure of nanocrystalline Y2O3:Eu prepared by a combustion reaction was analyzed by XRD and high-resolution electron microscopy. Compared with a large-scale particles, 5-nm Y2O3:Eu particles presented as distorted crystallite and rough surfaces. Luminescent and absorption properties of nano-Y2O3:Eu showed remarkably particle size effects. At Y2O3:Eu particle sizes smaller than 10 nm some new results were observed: (a) a red shift of the charge-transfer-state absorption; (b) new emission bands of Eu3+ in the 5D0 --> 7F2 region; (c) luminescent decay of energy level 5D0 of Eu3+ turning to a two-step exponential; and (d) a pronounced increase in quenching concentration and much lower phonon density compared with those of the bulk material. All these phenomena can be attributed to the effect of the softened lattice and surface state of the nanomaterial. The latter was confirmed by stronger excitation by the host absorption after the surface modification.