Long-lived luminescence from commonly used Apiezon compounds

Abstract

Long-lived (~12s) luminescence from Apiezon compounds (greases and wax) has been measured following ultraviolet or visible excitation in the temperature regime 8–300 K. A typical spectrum consists of a single Gaussian band centered near 2.2 eV. The intensity of this band is maximum at the lowest temperature investigated (8 K), decreases nonlinearly with increasing temperature, and becomes undetectable near 250 K. Spectral peak position and full-width at half-maximum remain approximately constant throughout this temperature interval for fixed measurement times. Time decay measurements at 8 K show an increase in peak position with increasing time lapse since optical excitation. The time dependence of peak intensities as a function of temperature can be described by I(t) = [A exp (−αt)] [1 + B{1 − exp (αt)}] , consistent with P-type delayed fluorescence arising from triplet-state deexcitation in organic molecules. Although the composition of Apiezon compounds is proprietary they are known to contain a high proportion of hydrocarbons. The single Gaussian emission band and long fluorescence lifetime is consistent with previous observations on hydrocarbons. Because Apiezon compounds are easily excited, yielding fairly intense luminescence, caution must be exercised when using them in optical experiments.