MgO film is coated on the surface of the phosphor.

　　The coating method is as follows: conjugate acid-base system with pH value of 8.0 ~ 12.0 was used to prepare the pH buffer solution, and the concentration of the buffer solution was greater than 0.1M and less than 2M. According to the ratio of MgO and phosphor weight ratio of (0.25 ~ 15)∶100, the corresponding amount of water-soluble magnesium salt was weighed and prepared into the water-soluble magnesium salt titration solution with concentration of 0.01 ~ 1M.

　　The phosphor powder was put into the pH buffer solution, and the phosphor powder suspension with the concentration of 0.2 ~ 5% was prepared. The phosphor powder was dispersed in the buffer solution by stirring and ultrasonic dispersion.

　　Phosphor powder suspending liquid is heated to 20 ~ 70 ℃ and the temperature control in the 100 r/m ~ 300 r/m speed stirring and water soluble magnesium salt titration solution drip into the phosphor powder suspension, the dropping speed of 2 ~ 15 ml/min, and then continue to heat preservation and mixing 30 ~ 180 min, coated phosphor powder suspending liquid, after separation, washing, dehydration, drying under 60 ~ 120 ℃, and the moisture content of the coated phosphor is less than 0.25%, 200 ~ 400 ℃ calcination under 1 ~ 3 h, along with the furnace air cooling.