Influence Of Surface Quenching Effects On Luminescent Dynamics Of Ion Centres In Nanomaterials

ABSTRACT: Quantum confinement effect and surface effect play important roles inspectroscopic properties of nanomaterials. For isolated ion centers, however, the radiusof the outer shell electron orbital is only about 0.1 nm, confinement by the size ofseveral or even tens of nanometers could not evidently influence the distribution of theirelectronic clouds, hence produces no significant variation in their energy levels andtransition probabilities. Surface effect, instead, becomes the most important factoraffecting their spectroscopic properties. In this paper, a model describing surfacequenching of isolated ion centers in nanocrystals was proposed based on the energytransfer between the doped ions and the nanocrystalline surface quenching centers.Compared to the decay curves of different nanocrystalline systems using this model, itwas proved that the model was in good agreement with the experimental results. So itwas proved that the surface quenching effect led to enhance nonradiative relaxation ofthe ion centers, and the difference in quenching rates of the ions at different sites in thenanoparticles made the decay curve under nonselective excitation being nonexponential.Results are summarized as follows:A surface quenching model was proposed for 0-dimensional nano-material. Byconsidering static energy transfer by electric dipole-dipole interaction between therandomly distributed ions to the surface quenching centers in an isotropic, continuumnanosphere, energy transfer rate X(r), quantum efficiency of doped ionsηand the decaycurve under nonselective excitation F(t) were calculated.Eu(DBM)₃TPPO nanoparticles with the sizes of about 10nm were prepared byreprecipitation method in alkalescent and neutral environment. The luminescence of thenanoparticles prepared in neutral environment were quenched seriously by the H₂Omolecules and the nanoparticles aggregated evidently; while the nanoparticles preparedunder alkalescent environment were well dispersed and the Eu³⁺ luminescence keptunchanged with time. The decay curve of Eu³⁺ (⁵D₀→⁷F₂) in Eu(DBM)₃TPPOnanoparticles measured under nonselective excitation is nonexponential, and it is ingood agreement with the decay curve calculated by the surface quenching model.Decay curve calculated with this model is also in good agreement with that of the⁴T₁→⁶A₁ emission of Mn²⁺ in ZnS nanocrystalline published in references. So it wasproved that the influence of the surface quenching to the luminescence of ion centers in nanoparticles and the applicability of our model.