Experiments on Electroluminescence

Abstract

A summary of recent observations of the properties of ZnS:Cu:Pb and ZnS:Cu:Pb:Mn electroluminescent phosphors is reported. The experiments include studies of the optical and electrical response of these phosphors dispersed in "Lucite" to sudden changes in a constant applied field, as well as microscopic studies of the luminescence of individual particles. Both green and yellow phosphors were studied. The most important results observed primarily on green phosphors are the following: Slow changes are found to take place in a phosphor in any given constant electric field, but a steady state is finally approached. A sudden departure from this state produced by changing the applied field will in general produce very little light compared to that produced on returning promptly to the conditions under which the steady state was established. Further, the luminescence in alternating electric fields of individual grains is extremely inhomogeneous, being restricted to small "pinpoints" or "spots" very much smaller than the individual particles. The spots studied luminesced only once per cycle.It is concluded that excitation of luminescent centers occurs primarily by ionization, with recombination and radiation occurring when subsequent electrical changes make this possible. Although excitation of luminescent centers to bound states followed by prompt radiation does occur, under the conditions of these experiments this process is of secondary importance in producing light in all the phosphors studied, and is quite negligible in the green phosphors. These and other results are discussed in connection with the several possible mechanisms by which electric fields may bring about the excitation of luminescent centers.

Studies on the Orientation of ACEL ZnS:Cu Particles in Applied AC Fields

“…Also lines (or streaks) of emitted light in our case parallel to the fault planes are observed in some crystals in Figures 4, 5 and 6 (particularly the latter which shows two crystals under higher magnification), possibly explaining the "streaks" of light observed by others in previous studies. [12][13][14][15][16]24,27 A FESEM micrograph is presented in Figure 4d of the phosphor particles shown in the previous optical images in Figure 4a to 4c, the exact orientation of all particles is now clearly revealed. The brightest ACEL emitting particles (see Figure 4c) are shown to be oriented with cubic [111] axis at various angles, generally in a perpendicular direction to the applied alternating electric field that radiates across the gap between conducting tracks.…”

“…23 This view that the orientation of ZnS:Cu particles relative to the applied field direction is of significance with regards to ACEL emission has also been supported by other workers. 8,[13][14][15][16][17] Low magnification optical microscope studies reveal that commercial ACEL panels when excited with an electric field have a speckled appearance, the particles have a diameter between 10 to 50 micrometers are observed to emit with different intensities independent of particle size. 24 A number of particles in all ACEL panels do not display electroluminescence.…”

“…This model found acceptance due to the observation by Fischer 12,13 of localized double comets of light that were emitted alternately on field reversal along the direction of the stacking faults and subsequently reported by other workers. 14,15 In addition to localized comets of light, spots and patches have also been observed indicating that the light emission is inhomogeneous in this material. [14][15][16] …”

“…14,15 In addition to localized comets of light, spots and patches have also been observed indicating that the light emission is inhomogeneous in this material. [14][15][16] …”

Электролюминесценция

“…Вопрос будет рассмотрен более детально в разделе 9, а. Эти факты делают совершенно понятной зави-симость от частоты. Сообщалось уже, что электро-люминесценция происходит только в небольшой части рошка, помещенного 136,142,143 ооъема по-в образец или одиночного кристал-…”