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Model of ageing process of electroluminescent structures The electroluminescent structures are more and more widely applied, as the light emitted by them is characterised by low power consumption, uniform emission from the whole active surface, the possibility of continuously variable control of light . These structures are however subject to the ageing process, the rate of which depends upon many factors. Under the influence of the electric field applied and climatic operating conditions, i.e. temperature and humidity, irreversible changes take place in the electroluminophore structure that result in a systematic decrease in luminance of the light emitted. In order to propose a model of the ageing process of electroluminescent structures and determine the dynamics of luminance change processes, the authors have screen-printed the thick-film electroluminescent structures on flexible substrates and carried out a series of operation tests where the major parameter assessed was the luminance value. 2. SAMPLE PREPARATION In Fig. 1, a schematic diagram of the sandwich electroluminescent structures composed of screen-printed layers is presented. Fig. 1. Arrangement of layers in an electroluminescent structure: 1 – polyester foil with an ITO film; 2 – transparent thermosetting resin; 3 – electroluminophore grains; 4 – dielectric layer; 5 – conductive layer (opaque). Rys. 1. Układ warstw w strukturze elektroluminescencyjnej: 1– folia poliestrowa z warstwą ITO; 2 – przeźroczysta żywica termoutwardzalna; 3 – ziarna elektroluminoforu, 4 – warstwa dielektryczna; 5 – warstwa przewodząca. The following polymer ink films have subsequently been deposited onto the polyester substrates of the dimensions of 30 mm x 20 mm, pre-coated with an ITO 118
Z. Porada, M. Cieź, W. Prochwicz (Indium Tin Oxide) layer of a sheet resistance of 400Ω/‪: an electroluminophore film whose major component are the grains composed of the Cu-activated and Cl- -co-activated ZnS crystals suspended in the resin, a dielectric layer composed of the BaTiO 3 powders also suspended in the resin, and a conductive layer, a composition composed of silver powders and thermosetting resin. After deposition, each layer was cured at a temperature of approx. 130°C for 30 minutes. After the curing processes have been completed, the structure underwent visual inspection and luminance measurements were subsequently carried out at the a.c. voltage with an amplitude value of 100 V at a frequency of 400 Hz. The luminance measurements were performed with a Tektronix J18 luminance meter and the error of measurement did not exceed 5%. 3. TEST PROCEDURES The following tests have been carried out on fabricated samples: - a reliability test at the temperatures of +20°C, +40°C, +60°C, at a supply voltage U p-p = 180 V, f = 400 Hz. The results of the test are shown in Fig. 2, Fig. 2. Changes of luminance during reliability tests. Rys. 2. Zmiany luminancji podczas badań niezawodności. - a reliability test at the ambient temperature of +20°C, at variable supply voltages and a constant frequency 400 Hz. The results of the test are shown in Fig. 3, - a reliability test at the ambient temperature of +20°C, at variable frequency and a constant supply voltage 150 V. The results of the test are shown in Fig. 4, - a moisture resistance test under conditions of the prolonged exposure to moisture 119
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INSTYTUT TECHNOLOGII MATERIAŁÓW E
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SPIS TREŚCI ARTYKUŁY WPŁYW PROMI
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6 Wpływ promieniowania jonizujące
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2. STRUKTURA I DEFEKTY W YAP I LN W
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Wpływ promieniowania jonizującego
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16 Wpływ promieniowania jonizując
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2. MICROVIA FORMING PROCESS Analysi
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Analysis of blind microvias forming
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