Spectroscopic characterization of Er3+-doped CaF2 nanoparticles: Luminescence concentration quenching, radiation trapping and transition probabilities

Abstract

Er3+-doped CaF2 nanoparticles (NPs) with variable dopant concentration were synthesized by a direct precipitation method. X-Ray Powder Diffraction, SEM and TEM were used to analize the crystalline structure and morphology. The spectroscopic characterization, as function of the Er3+ content, has been performed under CW and pulsed excitation. Under steady state conditions, it has been found that the intensity of the main emission bands is affected by luminescence quenching processes. The population dynamics, recorded under pulsed excitation, confirms not only the existence of quenching processes but also the occurrence of radiation trapping. The intrinsic transition probabilities of the main Er3+ emitting manifolds, in absence of quenching and radiation trapping, have been estimated through a procedure commonly used in bulk doped materials. A modified Judd-Ofelt analysis has been performed to determine the radiative transition probabilities, radiative lifetimes and branching ratios of the Er3+ levels. Finally, an estimation of the gap law in these NPs is given