Improved Moisture Resistance And Device Application Of Fluoride Red Phosphor

White light-emitting diodes（WLEDs）are widely used in indoor lighting and liquid crystal displays due to their high luminous efficiency,green environmental protection,and simple preparation.The popular WLEDs packaging method on the market is mainly a combination of blue In Ga N chips and YAG:Ce³⁺(Y₃Al₅O₁₂:Ce³⁺)yellow phosphors.However,adding only yellow phosphors to WLEDs will cause some problems,such as high light source color temperature（CCT>4000 K）,low color rendering index（CRI,Ra<80）.Finding suitable red phosphors is the key to improving the light and color performance of WLEDs.Recently,Mn⁴⁺-doped fluoride phosphors have attracted great attention in the field of solid-state lighting and have been rated as the most promising red phosphors in WLEDs.Mn⁴⁺doped fluoride red phosphor has many advantages,such as narrow red light emission,high quantum yield,excellent thermal stability and low production cost.However,the Mn⁴⁺-doped fluoride red phosphor has the problem of poor moisture resistance.In humid environment,Mn⁴⁺is easily hydrolyzed into manganese oxides and hydroxides,resulting in a decrease in the luminous efficiency of the phosphor,which has a certain impact on the practical application in the field of WLEDs.Therefore,the research direction chosen in this paper is the strategy and mechanism of improving the moisture resistance of Mn⁴⁺doped fluoride red phosphor.The main research content and results of this article are as follows:（1）A strategy to passivate the surface with glyoxylic acid（GA）is proposed.Based on the reducibility of GA solution,it effectively removes Mn⁴⁺on the surface of fluoride,forming a homogeneous K₂Si F₆ protective shell layer on the surface of K₂Si F₆:Mn⁴⁺red phosphor.The phosphor K₂Si F₆:Mn⁴⁺-GA passivated by glyoxylic acid exhibits high luminous efficiency and good moisture resistance.The luminous intensity of phosphor K₂Si F₆:Mn⁴⁺-GA is about 99.7%of KSFM luminous intensity.After 360 hours of water immersion,K₂Si F₆:Mn⁴⁺-GA phosphor can still maintain 97.5%of the initial fluorescence intensity,and the internal quantum yield is as high as 98.43%.The strategy of using glyoxylic acid solution to improve the humidity resistance of phosphors is also applicable to K₂Ge F₆:Mn⁴⁺and K₂Ti F₆:Mn⁴⁺phosphors.The hydrolyzed fluoride phosphor can also be repaired by glyoxylic acid solution,the body color is restored to the original yellow,and the luminous intensity can be restored to 99.1%of the unhydrolyzed K₂Si F₆:Mn⁴⁺.With passivated fluoride phosphor as the red light component,when the correlated color temperature（CCT）of the packaged WLED is 3249 K,the lumen efficiency is as high as 126.95 lm/W and the color rendering index（Ra）is higher than90.After 500 hours of aging（temperature 85o C,humidity 85%）,WLEDs can still maintain 85%of the initial lumen efficiency.（2）The-hydroxy acid lactobionic（LA）passivation strategy is used to improve the moisture resistance of K₂Si F₆:Mn⁴⁺phosphors.The luminescence intensity of LA passivated fluoride(K₂Si F₆:Mn⁴⁺-LA)maintains 99.4%of KSFM.After 360 hours of water immersion,the luminous intensity of K₂Si F₆:Mn⁴⁺dropped to 63%,while the K₂Si F₆:Mn⁴⁺-LA phosphor could still maintain 87.5%of the initial luminous intensity.Lactobionic acid solution can also improve the humidity resistance of phosphors K₂Ge F₆:Mn⁴⁺and K₂Ti F₆:Mn⁴⁺.In addition,the lactobionic acid solution can also repair the hydrolyzed fluoride phosphor and restore its luminous properties.WLEDs packaged with surface passivated fluoride as the red light component have high lumen efficiency（130.61 lm/W）,low color temperature（3518 K）and high color rendering index（88.5）.After 500 hours of aging under high temperature and high humidity（temperature 85o C,humidity 85%）,the WLEDs can still maintain 90.5%of the initial lumen efficiency.In this work,the experimental procedure of treating fluoride phosphors with glyoxylic acid and lactobionic acid solutions is simple and low in cost,which provides a reference for the mass synthesis of fluoride phosphors with good moisture resistance.