Fluorescence quenching in KNdxGd1-xP4O12 crystals studied using an isolated ion-pair interaction.

Abstract

The quenching of fluorescence from the $^{4}\mathrm{F}_{3/2}$ excited state of ${\mathrm{Nd}}^{3+}$ in ${\mathrm{KNd}}_{\mathrm{x}}$${\mathrm{Gd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{P}}_{4}$${\mathrm{O}}_{12}$ (abbreviated KNGP) crystals is investigated. A rich satellite structure of the 1.6-K excitation and absorption spectra is observed and related to the neodymium pairs. Single ${\mathrm{Nd}}^{3+}$ ions in different crystal-field sites were also detected. The ion-ion interaction is directly analyzed by lifetime measurements of Nd-pair satellites in weakly concentrated samples. With the use of the discrete host structure model and the measured microscopic interaction parameters, the shape of the fluorescence decay in strongly concentrated crystals is predicted. Comparison of the theoretically evaluated cross-relaxation rate between two neighboring ${\mathrm{Nd}}^{3+}$ ions and the quenching rates of the satellites indicates that the ions are coupled by the electric dipole interaction. The $^{4}\mathrm{F}_{3/2}$\ensuremath{\rightarrow}${\mathrm{}}^{4}$${\mathrm{I}}_{9/2}$ fluorescence spectra are measured as a function of excitation wavelength and time delay after the excitation pulse. These laser site-selection time-resolved spectroscopy results indicate that at low temperature there is no fast spectral diffusion among the ${\mathrm{Nd}}^{3+}$ ions in KNGP.