The Study Of Plasma-assisted Atomic Layer Deposition Of Al₂O₃ Coating Phosphor Powders For Light Emission Diode Application

With the widespread use of white light-emitting diodes（LEDs）,the instability and short life of phosphors used in white LEDs have become a bottleneck and restricted their development.At present,phosphors,especially red and green phosphors,meet the challenge of poor moisture resistance and sensitivity in the humid environment.In this thesis,atomic layer deposition technique with a vibrating fluidized bed equipment is utilized to deposit Al₂O₃ protecting the phosphor from humidity.The trimethylaluminum（TMA）is admitted as a precursor,water or oxygen plasma as an oxidant,respectively,in ALD process for coating the surface of silicon-based nitride phosphors and silicate phosphors.The grown coatings by thermal atomic layer deposition（T-ALD）and plasma-assisted atomic layer deposition（PA-ALD）are analyzed by scanning electron microscopy,transmission electron microscopy,X-ray energy spectrum analysis,Fourier transform infrared spectroscopy,Zeta potential meter,transient steady-state fluorescence spectrometer,pH meter,etc,for surface morphology,shape conformality,film composition,powder dispersibility,luminescence properties,water resistance,thermal stability,respectively.After the performances are s compared,the following conclusions were obtained:（1）T-ALD and PA-ALD aluminum oxide can realize high conformal coating the powder surfaces,and the growth rates of alumina are about 0.1 nm/cycle and 0.15nm/cycle,respectively;（2）When T-ALD and PA-ALD Al₂O₃run the cycles of 500 and 400,respectively,a better moisture resistance of the phosphor can be achieved.Among them,PA-ALD Al₂O₃ demonstrates a better water blocking effect than that done by T-ALD Al₂O₃,and the coated powder remains almost unchanged pH value after immersing into water;（3）The alumina coatings exhibit little effect on the luminescence intensity of the powders but not color temperature,which is relatively lowers after coating.The T-ALD Al₂O₃ coating causes an increaseof color temperature;（4）T-ALD and PA-ALD Al₂O₃ coating phosphors improve the thermal stability of the phosphor.