Output luminescence of Zn2SiO4 : Mn phosphor saturates under intense vacuum ultraviolet radiation having a relatively high excitation duty ratio. The saturation is attributed to the depletion of activators at the ground level. This depletion originates from the long decay time constant of the phosphor. The saturation mechanism is explained analytically using a simple model, and the conditions for efficient phosphor excitation are derived.
Mercury‐free flat discharge lamps with diagonal sizes ranging from 5.0 to 5.2 inches have been developed for LCD backlights. The lamps have simple structures with insulated electrodes. Uniform discharges are obtained by adjusting drive pulse voltage and waveforms. As lamp diagonal becomes larger, luminance and efficacy increa‐se, and the dimming can be varied in wider range.
An intense vacuum ultraviolet spike 0.2 μs in width is observed at the initial stage of low-pressure Xe discharge, i.e., Xe Townsend discharge, in submillimeter tubes. The intensity of the 147 nm resonance line reaches 1.3 W/cm2, about 200 times stronger than that obtained from the steady-state Xe positive column. Efficiency of the vacuum ultraviolet radiation exceeds 24%, or 32 lm/ W when green phosphor is excited, four times higher than that of the positive column, or more than an order of magnitude higher than that of the negative glow. This high intensity and efficiency originate from the optimized electron energy which can be adjusted externally by changing the electric field and pressure, contrary to that in the positive column or negative glow. Another important feature of the Townsend discharge is its wide dynamic range of operation, which is advantageous when driving a panel having a large number of cells with scattered discharge characteristics. Consequently, a gas discharge display panel utilizing the Townsend discharge has more than an order of magnitude higher efficiency than the positive column or negative glow panels.
The luminous efficacy of a Zn2SiO4:Mn-coated, low-pressure Xe-positive-column fluorescent tube is found to be as high as 100 l/W which corresponds to an electric to 147-nm radiation energy conversion factor of 66%. This high efficacy can be attained under conditions (pressure)×(column diameter)≃1 Torr cm and (current density)?3 mA/cm2.
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