Blue luminescence of SrTiO3 under intense optical excitation

TL;DR

This study investigates the blue luminescence of SrTiO3 under intense UV excitation, revealing temperature-dependent color transitions, bimolecular recombination, and intrinsic defect-related emission mechanisms.

Contribution

It provides new insights into the luminescence mechanisms of SrTiO3, highlighting the roles of defect states and ruling out Auger processes as dominant recombination pathways.

Findings

Blue-to-green transition with temperature in pure samples

Bimolecular electron-hole recombination dominates initial decay

Luminescence centers likely intrinsic structural defects

Abstract

The blue-green photoluminescence emitted by pure and electron-doped strontium titanate under intense pulsed near-ultraviolet excitation is studied experimentally, as a function of excitation intensity and temperature. Both emission spectra and time-resolved decays of the emission are measured and analyzed in the framework of simple phenomenological models. We find an interesting blue-to-green transition occurring for increasing temperatures in pure samples, which is instead absent in doped materials. The luminescence yield and decay rate measured as a function of temperature can be modeled well as standard activated behaviors. The leading electron-hole recombination process taking place in the initial decay is established to be second-order, or bimolecular, in contrast to recent reports favoring a third-order interpretation as an Auger process. The temporal decay of the luminescence can be described well by a model based on two interacting populations of excitations, respectively identified with interacting defect-trapped (possibly forming excitons) and mobile charges. Finally, from the measured doping and sample dependence of the luminescence yield, we conclude that the radiative centers responsible for the luminescence are probably intrinsic structural defects other than bulk oxygen vacancies.