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Physical review. B, Condensed matter

Fluorescence quenching by cross relaxation in La F3 : Pr3+

John Hegarty, David L. Huber, William M. Yen

Published May 1, 1982• 130 citations
Publisher

Abstract

We have investigated the process of quenching of fluorescence from the $^{3}P_{0}$ excited state of ${\mathrm{Pr}}^{3+}$ in La${\mathrm{F}}_{3}$ due to cross relaxation among the Pr ions. The fluorescence decay of the ensemble of Pr ions after pulsed excitation is measured as a function of temperature for Pr concentration of 20 mol%. About 12% of the ions are in nonquenching sites and contribute an exponential component to the decay. The remainder of the decay originates from the bulk of the ions in quenching sites. Cross relaxation occurs directly in steps after transfer within the inhomogeneous line. Knowledge of the dynamics occurring within the inhomogeneous line derived from fluorescence line-narrowing experiments is used to analyze the cross-relaxation process from a microscopic viewpoint based on a recent model for fluorescence in the presence of traps. At 2 K the decay is consistent with an electric dipole-dipole transfer mechanism with a nearest-neighbor quenching rate of 8.9 \ifmmode\times\else\texttimes\fi{} ${10}^{4}$ ${\mathrm{s}}^{\ensuremath{-}1}$ which is independent of temperature for $T<32$ K and which successfully predicts the observed decay rate in Pr${\mathrm{F}}_{3}$. The temperature dependence of the decay for $8\ensuremath{\le}T\ensuremath{\le}32$ K is well described by a hopping model for excitation trapping. For $T>35$ K an activation process becomes dominant consistent with the onset of cross relaxation involving the $^{1}D_{2}(5)$ and $^{3}H_{6}(1)$ states in which a 190-${\mathrm{cm}}^{\ensuremath{-}1}$ phonon is created.

DOI
10.1103/physrevb.25.5638

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The temporal dependence of the fluorescence line shape of Pr ion diluted in LaF3{\mathrm{F}}_{3}F3​ has been studied in detail. The line-shape study is based on the assumption that the cross relaxation between Pr ions dominates the nonradiative process. The ion-ion interaction has been directly probed by the two-ion cooperative absorption process under which a 3P0^{3}P_{0}3P0​ level lifetime dilation has been observed. The dilation effect can be suppressed when the spectral energy transfer is switched on by raising the temperature of the host crystal. The temporal behavior of the fluorescence line shape of the 1D2^{1}D_{2}1D2​ level has been systematically investigated. The "inhomogeneous" linewidth is found to be composed of a main central peak and a series of ion-pair satellites. The shorter decay lifetime of the ion-pair states results in the narrowing of the emission line shape at later times. The energy positions of the ion-pair states have been measured from the 1D2^{1}D_{2}1D2​ ion pairs up-conversion fluorescence process. The lifetime of the ion-pair states is determined by the coupling strength of the cross relaxation from an excited ion to its partner ion and hence varies according to the ion-pair separation. The decay under the inhomogeneous width is nonexponential in general. Based on the number of the distinguished ion pair levels, a concept of the sphere of influence is introduced. Following this model, an approach has been developed which allows us to study the decay characteristics. Systematical trends emerge from such analysis. The cross-relaxation coupling constants for ion pairs have been extracted from the decay curves and profiles of the ion-pairs line shape have been mapped out. Their peak positions agree with those obtained from 1D2^{1}D_{2}1D2​ ion-pair up-conversion fluorescence measurements.
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