Regular Article

Impact of damaging and recovery on the temperature dependence of the work function of oxide electrodes in fluorescent lamps

¹ Institut für Physik, Lehrstuhl für Experimentalphysik II, Universität Augsburg, Universitätsstraße 1, 86159 Augsburg, Germany
² LEDVANCE GmbH (former part of OSRAM AG), Berliner Allee 65, 86136 Augsburg, Germany

^* e-mail: Reinhard.Langer-physik@t-online.de
^† Present address: Deutsches Patent- und Markenamt, Zweibrückenstraße 12, 80331 München, Germany. This article represents the author's personal opinion and not that of the German Patent and Trademark Office.
^‡ Present address: Instrument Systems Optische Messtechnik GmbH, Kastenbauerstraße 2, 81677 Munich, Germany.

Received: 2 July 2021
Received in final form: 26 August 2021
Accepted: 30 August 2021
Published online: 29 September 2021

Abstract

In the present work the work function of electrons for oxide cathodes in operating fluorescent lamps is measured before and after damaging the cathodes by cold starting of the lamp. A strong increase of the absolute value and a decrease of the temperature dependence of the work function is observed. The values recover partly after operating the lamp for a certain time. The results are interpreted as the consequence of a thin metallic layer generated during cold starting at the surface of the oxide and its effect on the depletion of electrons of donor-like colour centres (appearing in the oxide due to oxygen vacancies) under the ultraviolet radiation present in an operating fluorescent lamp, and on the magnitude and temperature dependence of the work function in the plated regions, invoking the patch effect to generate an averaged value of the work function, which is then assumed to be observed experimentally. Moreover, barium surface states are considered, yielding reasonable values for the not plated regions, when calculating the work function, as well for the assumption of a depletion of also these states by ultraviolet radiation, as also when only regarding a thermal excitation of the surface states applying the Fowler equation. Finally, a model of a diffusion governed dynamical equilibrium yielding a T^3∕2 dependence for the donor concentration is proposed.