December 09, 2019

Study on phosphor coating and lamp coating

In recent years, in the wide application of rare earth trichromatic phosphors, the problem of light decay has always been a focus of attention. In order to improve the light decay of rare earth trichromatic phosphors, especially BaMgAl10O17:Eu blue powder (BAM powder), it is proposed to surface coat the phosphor particles to form a protective film on the surface of the powder to reduce short-wave ultraviolet radiation. Impact of harmful factors such as bombardment, adsorption and deposition of mercury; or coating a protective film on the surface of the lamp glass to reduce the interaction between the surface components of the glass and mercury and the migration to the phosphor coating. These measures can reduce the light decay of the fluorescent lamp during use and improve the lumen maintenance of the fluorescent lamp. In the research report on protective films, the effects of Al2O3 films and the like in various film layers have been confirmed. The actual effect of the protective film application is related to the material properties, the coating conditions, the coating state of the film, and the like. In the experiment, the sol method was applied to coat the BAM powder with a nano-sized aluminum sol, and a BAM phosphor coated with an aluminum oxide film layer was obtained. The surface morphology and composition of BAM powder were studied by SEM and XPS. The adsorption and deposition of mercury on the surface of phosphor powder was carried out with uncoated BAM powder as control. It was also the main factor causing fluorescence light decay. The change of the amount of mercury adsorbed on the surface of the BAM phosphor was also examined to study the effect of the coating on the adsorption and deposition of mercury on the surface of the powder. At the same time, we used aluminum sol to coat the glass tube used in the fluorescent lamp, so that the surface of the glass was coated with a thin layer of aluminum oxide film and the film was tested. Then, the phosphor powder was coated on the film layer to make a fluorescent lamp, and the light decay data of different ignition time was obtained. A series of experimental results show that the surface coating treatment of BAM phosphor can protect the powder, improve the surface stability, improve the thermal degradation performance of the phosphor, and reduce the adsorption and deposition of mercury. The synergistic effect is to reduce the light of the fluorescent lamp. The lamp coating treatment also reduces the influence of certain glass components and mercury during the operation of the fluorescent lamp, reduces the blackening of the lamp, protects the phosphor, and reduces the deterioration. The effect of the protective layer of the lamp can also be obtained from the fluorescent lamp. The reduction in light decay is confirmed. In the experimental part of the experiment, we used aluminum sol as the coating material, applied the sol-gel method, and applied the surface coating treatment to the BAM phosphor powder, and applied the coating treatment on the inner surface of the fluorescent glass tube. The aluminum sol used was synthesized by the laboratory, and it was found by SEM that the particle size of the sol particles was about 10 nm. (1) Treatment and testing of BAM phosphors 1 BAM powder coating treatment using sol method, reaction and adsorption composite means for BAM phosphor coating, after drying, burning, etc., the surface has alumina (γ- BAM powder of Al2O3) film layer. 2 Phosphor surface analysis The surface of the sample was measured by a Philips XL Scanning Electron Microscope (SEM) in the Netherlands. The Perkin-Elmer PHI 5000C ESCA System was used to measure the photoelectron spectroscopy (XPS) to analyze the aluminum oxide coating on the surface of the phosphor. 3 Luminescence performance test The same batch of BAM powder without surface coating treatment was used as a control to test the relative luminescence brightness of BAM powder after coating treatment; burning in air at 500 ° C, 550 ° C, 600 ° C, 650 ° C After 30 min, after cooling, the relative luminescence brightness was tested and the thermal stability of the coated BAM powder was compared. The coated powder and the control powder were respectively made into 7W double U-shaped monochromatic lamp and 18W3U-shaped monochromatic lamp, and ignited. At different times, the light decay test of the monochromatic lamp ignition point was carried out, and the effect of surface film treatment on the luminescence of the phosphor was studied. 4 Determination of mercury content on the surface of the powder. Fluorescent tubes after the ignition point are collected at different times. The phosphor samples on the inner wall of the tube are collected. After chemical treatment, the amount of mercury deposited on the surface of the powder is determined by cold atomic absorption (CVAAS) method. The same batch of powder sample control without coating treatment was used to understand the effect of the coating on the adsorption and deposition of mercury on the surface of the powder. (2) Treatment and testing of fluorescent glass tube 1 The inner surface coating treatment of the lamp is carried out by applying a method similar to that of the powder in the production of the lamp, and applying the sol to the glass surface in the fluorescent tube at an appropriate concentration and flow rate. After heating and baking at -500 ° C, the inner surface of the tube has a thin layer of a very transparent aluminum oxide (γ-Al 2 O 3 ) film layer. The test uses different concentrations of sol A and sol B as the sol coating film, and the A concentration is twice the B concentration. 2 Morphological analysis of the surface layer of the glass was taken by cutting the glass with the protective film and using a Philips XL30 scanning electron microscope (SEM) to measure the shape and thickness of the film formed on the surface of the glass. . 3 Light-fat test after lamp-making The 18W3U-shaped fluorescent lamp was made of the glass tube treated with the above coating film, and the light and light effect of the lamp were tested by the same batch of lamps without coating treatment. These lamps were ignited at different times for light decay test, and the improvement effect of the lamp coating treatment on the luminescent properties of fluorescent lamps was studied. RESULTS AND DISCUSSION (1) BAM phosphor powder 1 coated surface analysis of the phosphor powder can be observed from the SEM photograph: the BAM powder with a typical hexagonal crystal shape has a clear and flat corner. After the coating treatment, there is a clear crystal surface. A layer of fine grained coating. XPS analysis showed that the surface composition of the phosphor after coating by the sol method changed significantly, and the proportion of aluminum contained was significantly improved. The results are shown in Table 1. According to the calculation of the area occupied by various atoms, the coverage of the aluminum oxide film layer is about 90%. This film layer is very stable, and even after the steps of washing, coating, baking, and lamp making, the alumina coverage of the powder surface remains unchanged. 2 Thermal stability of the phosphor The relative luminescence brightness of the coated BAM powder was tested by the same batch of BAM powder sample without coating treatment; and the luminescence brightness attenuation was tested by burning at different temperatures in the air. Their thermal stability is compared, see Table 2. The test results show that the initial luminescence brightness of the coated phosphor is slightly lower than that of the control, but the brightness decay ratio after burning is significantly reduced. The brightness decay ratio after burning at 550 °C is 0%, while the control sample is 7 %. It can be seen that the coating treatment improves the thermal degradation performance of the BAM phosphor and improves the thermal stability of the BAM powder. 3 The light-fading performance of the phosphor lamp was prepared by coating the BAM powder with the uncoated control sample, and respectively made the 7W double U-shaped monochrome lamp group 2 and the 18W3U monochrome lamp group, and the ignition points were different at different times. The light decay data of the monochromatic lamp is shown in Table 3. The test results show that the initial light flux of the lamp made by the surface coating treatment phosphor is slightly lower than that of the control sample, but the light decay during the working process is smaller than that of the control sample, and the light transmittance of the 7W double U-shaped monochrome lamp after 1000 hours The maintenance rate was 79.8%. The luminous flux maintenance rate of the 18W3U monochromatic lamp after 1000 hours was 70.3% and 55.5%. The light attenuation of the coated powder sample lamp was reduced by 6.1% and 18.5%, respectively. It can be seen that the surface coating treatment of the phosphor is an effective method for reducing the decay of the fluorescent light. The amount of mercury deposited on the powder surface of the coating powder was measured by cold atomic absorption (CVAAS) method. The results are shown in Table 4. From the above results, it can be observed that as the lighting time is prolonged and the light decay of the fluorescent lamp increases, the amount of mercury adsorbed and deposited on the surface of the phosphor is also gradually increased, and the amount of mercury adsorbed and deposited on the surface of the coated phosphor is significantly smaller than that of the control sample. . This result indicates that the coating treatment can protect the powder and reduce the deposition of mercury on its surface. The above test of the BAM powder indicates that the BAM phosphor coated with the stabilized alumina film layer can be obtained by the sol method using the aluminum sol as the coating material, and the thermal stability of the coated phosphor is improved. The phenomenon of light decay after lamp making and the phenomenon of adsorption of mercury on the surface of the powder during work have also been significantly improved. (2) The material obtained by the film-treated fluorescent tube sol method often has some special advantages. Compared with the method of coating a glass tube with a coating liquid prepared by using ultrafine γ-Al 2 O 3 powder, the coating effect obtained is different. The glass coated with the aluminum sol and heat treated remains transparent, which is the same as the uncoated glass tube; careful observation shows that the glass surface is covered with a very thin layer of aluminum oxide (γ-Al2O3). Membrane layer. The film thickness of the alumina is related to factors such as the sol concentration, the flow tube speed, the coating time, the heating temperature, and the like used in coating the tube. In this experiment, the sol is applied to the vertical tube of different conditions of the glass tube, and after heating and baking at 400-500 ° C, the thickness of the general transparent film layer can reach 100-500 nm, and the coverage on the glass surface is complete. . The SEM photograph of the Al2O3 film on the surface of the glass shows that the thickness of the Al2O3 film formed by heating with a sol A vertical flow tube and baking at 500 °C is about 300 nm, and the surface of the glass is completely covered and covered uniformly. It can be maintained even after washing. The glass tube treated with the above sol A or sol B coating film was respectively made into an 18W3U-shaped fluorescent lamp, and the luminous flux and the light effect of the lamp produced by the same batch of glass tubes which were not coated with the film were tested. The light decay test of the coated lamp tube was carried out at different ignition times, and the measured result data is shown in Table 5. It was observed from the experiment that the initial light flux of the fluorescent lamp made of the coated glass tube is similar to that of the control sample, and the light flux of the sol A coated tube with a larger concentration is slightly lower; with the extension of the lighting time, the coated glass is coated. The light passage of the lamp made by the tube gradually exceeded the control sample, the attenuation of the light passage was lower than that of the control sample, and the light decay of the sol A coated tube was especially improved. The light decay after 1000 hours was lower than that of the control sample by 3.6%, after 3000 hours. The light decay was lower than 7.0% of the control, and the light decay after 5000h was lower than that of the control 7.5%; the blackening phenomenon of the fluorescent lamp made by the coated glass tube was also significantly reduced compared with the control. It can be seen that the sol-coated aluminum sol can form a uniform transparent alumina (γ-Al2O3) protective film on the fluorescent glass tube, reduce the influence of some glass components and mercury during the operation of the fluorescent lamp, and improve the blackening of the lamp. In other words, the protection of the phosphor reduces the degree of deterioration, thereby reducing the light decay of the fluorescent lamp. The above series of experimental studies show that the use of sol method with aluminum sol as coating material, surface film treatment of BAM phosphor powder, and coating of protective film on fluorescent glass tube are of practical significance for improving the light decay of fluorescent lamps.


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