| When using energy-saving lamps, a kind of very popular light, the problem of its darkening circle could not be ignored. The darkening circle, on the one hand, breaks the beauty of the total light, on the other hand, decreases the lumen maintaining rate, and reduces the service life of the energy-saving lamps. So studying and solving the problem of darkening circle of energy-saving lamps are very realistic. In this paper the word "darkening circle" refers to the color change near and around filament in the energy-saving lamp tube. The simple description is that the part of the tube close to the filament is yellow, and much later become black.In this paper, the inner wall surface coated with phosphors was observed with super depth microscope. We could see the imperfection of accumulation of phosphor powder; there were some holes more or less. These holes was due to the distribution of powder particle size was not very concentrated, and holes appeared when organic matter and gas escaped from phosphors powder layer during grilling light tube. And these holes increased the surface roughness, and then increased the surface area of bombardment by ions indirectly. Thus, the darkening circle of light tube appeared more easily.Trichromatic phosphors used in coating a lamp as phosphor powder layer was tested by XRD, and the indicative composition was red powder (Y0.95Eu0.05)203, green powder Ce0.67Tbo.33MgAl11O19, blue powder Ba0.956Mg0.9i2Al10.088017(Eu2+). And Through their emission spectrum (excited by254nm), red powder had a strong emission peak at610nm (transition of5D0â†'7F2), and weak emission peaks of D0â†'7F0,5D0â†'7F1,5D0â†'7F3,5D0â†'7F4; green powder had the strongest emission peak at543nm (5D4â†'7Fs), another less stronger emission peak at486nm (5D4â†'7F6), two weak peaks in the584nm (5D4â†'7F4),620nm (5D4â†'7F3); blue powder had strongest emission peak at454nm, belonging to the5dâ†'4f transition.Also SEM analysis was made on the surface of parts of the fluorescent tubes with darkening circle. It could be clearly observed that some very fine powder material that was attached to the surface.And the average particle size of the fluorescent particles in the powder layer is about4.51μm. By electron probe X-ray microscopy test on darkening circle parts and non-darkening circle parts, the results informed that the blackening material was composed of SrO, generated by electronic powder of the filament, and Hg oxides.Then, based on the principle of photoluminescence of phosphor, the decrease of photoluminescence intensity of anti-embedded core-shell structure phosphor was talked. The reason for that could be explained by following:(1) reduction of the effective ion concentration;(2) defects distribution probability increased when phosphor as shell;(3) nuclear layer blocked some of the energy transfer path, an increase of non-radiative transition probability. The factor that caused the decrease of photoluminescence intensity of anti-embedded core-shell structure phosphor was complex, and it was needed to find appropriate mathematical model for the theoretical calculation, as well as accurate experimental verification. |
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