Smooth pyroelectric luminescence in β-BaB2O4 single crystals via Fowler-Nordheim tunneling

Abstract

The smooth pyroelectric luminescence in β-BaB2O4 single crystals is investigated for low ambient pressures (down to 10-6 mbar) and temperature changes, in particular between 235–250 K for heating and 240–255 K for cooling cycles respectively. This faint, continuous emission of light due to temperature-induced changes of permanent polarization is brought about by charge carrier recombination inside the crystal, contrasting the well-known spike-like emission due to discharges in the ambient atmosphere. A microscopic model of the luminescence allows the description of the time-dependent pyroelectric luminescence, in particular the determination of deep trap potentials that are otherwise inaccessible to thermal activation. Using this model, we show that the behavior of this emission in the polar β-BaB2O4 crystals is consistent with the release of trapped electrons by Fowler-Nordheim tunneling under the influence of intense electric fields generated due to the pyroelectric effect. We also discuss the barrier lowering of both Coulomb and Dirac potentials through the Poole-Frenkel emission but only achieve good fitting of the experimental data for unrealistic combinations of values of the electron emission rates, capture cross-section, activation energies and high-frequency permittivity.