Spectral and time decay analysis of photoluminescence excited in the A band region in KCl:Pb

Abstract

AbstractThe A band spectral region in KCl:Pb is studied from the point of view of the optical absorption spectra, photoluminescence (emission and excitation) spectra, and the luminescence lifetime measurements in the temperature range 15 to 320 K. The sensitive ITC technique is exploited as a parallel tool to monitor and check the solution state of the impurity in order to rule out the additional and unwanted complications arising from the presence of aggregates. As a consequence only very dilute (4 to 6 ppm) and quenched samples are chosen to perform the detailed and systematic analysis of the photoluminescence spectra. The emission and excitation spectra do not depend significantly on the wavelength of the exciting and emitted light respectively, while their shape depends strongly on the temperature. The careful analysis of the emission spectrum, which looks asymmetric and apparently structureless, suggests that two Gaussians are contributing to it (main band and red side band, with associated average phonons of 1.25 × 10−2 and 1.6 × 10−2 eV, respectively) for T < 120 K, while a third weaker component seems to increase on the high energy side (violet side band) for T > 120 K. The luminescence time decay is complex exhibiting three distinct lifetimes: the length of two of them (τ1 = 30 and τ2 = 160 ns) is temperature independent, while the third one τ3 is strongly temperature‐dependent. The comparison between the intensity behaviour versus temperature both, of the time decay components and of the emission spectral components brings to a tentative attribution of τ1 to the main band, τ2 to the violet side band, and τ3 to the red side band. A scheme for the excited state energy levels, from which the emission excited by A light takes place is discussed both, by taking into account the dynamical Jahn‐Teller effect and the role of the neighbouring cation vacancy.