Temperature dependence of radiative and non-radiative decay in the luminescence of one-dimensional pyridinium lead halide hybrids

Abstract

The photoluminescence properties of organic–inorganic pyridinium lead bromide [(pyH)PbBr₃] and iodide [(pyH)PbI₃] compounds were investigated as a function of temperature. The inorganic substructure consists of face-sharing chains of PbX₆ octahedra. Diffuse reflectance spectra of the compounds show low energy absorption features consistent with charge transfer transitions from the PbX₃ chains to the pyridinium cations. Both compounds display extremely weak luminescence at room temperature that becomes strongly enhanced upon cooling to 77 K. Broad, featureless low energy emission (λ_em > 600 nm) in both compounds have large Stokes shifts [1.1 eV for (pyH)PbBr₃ and 0.46 eV for (pyH)PbI₃] and are assigned to transitions from self-trapped excitons on the inorganic chains whereas emission at higher energy in (pyH)PbBr₃ (λ_em = 450 nm) is assigned to luminescence from a free exciton state. Analysis of data from temperature-dependent luminescence intensity measurements gives activation energies (E_a) for non-radiative decay of the self-trapped excitons in (pyH)PbBr₃ and (pyH)PbI₃, (E_a = 0.077 eV and 0.103 eV, respectively) and for the free exciton in (pyH)PbBr₃ (E_a = 0.010 eV). Analysis of temperature dependent luminescence lifetime data indicates another non-radiative decay process in (pyH)PbI₃ at higher temperatures (E_a = 0.17 eV). A large increase in the luminescence lifetime of (pyH)PbI₃ below 80 K is consistent with thermalization between triplet sublevels. Analysis of the luminescence power dependence for (pyH)PbI₃ shows superlinear response suggestive of quenching by static traps.