2008 Volume 92 Issue 11 Pages 762-768
The work function of an oxide-coated tungsten filament in low pressure Hg discharge lamps was measured using the photoelectric effect with and without discharge. The plasma had been excited in a lamp with 2.45-GHz microwaves to reduce the power loading to the electrodes, which made the measurement of photoelectric current from the electrodes possible in plasma. Lasers with wavelengths of 325, 405, 532, and 633 nm irradiated the surface of the electrodes to induce photoelectric current. The work function of the electrode of an as-received lamp was determined to be 2.5 eV. Discharge operation of the lamp reduced the work function by activating the oxide-coated materials. The lowest observed work function ranged from 2.2 to 2.3 eV.