Improvement Research On Moisture Resistance Of Mn⁴⁺ Doped Fluoride Red Phosphor

In recent years,Mn⁴⁺doped fluoride phosphors as red components have attracted widespread attention in the fields of liquid crystal display?LCD?and solid-state lighting?SSL?.Although fluoride phosphors with a narrow emission at around 630nm exhibit unique luminescence performance under blue light excitation,the deterioration of luminescent properties as a result of obvious hydrolysis has limited their large-scale application.Therefore,this paper selects K₂SiF₆:Mn⁴⁺or K₂TiF₆:Mn⁴⁺phosphors as the research objects.From two perspectives of straight-forward preventive and reverse restoration,the surface modification of fluoride phosphors aims to achieve the experimental purpose of not losing the initial brightness of the phosphors and improving their moisture resistance,so as to further expand their scope of application.The research content and results are as follows:?1?Treating K₂SiF₆:Mn⁴⁺red phosphor with a seed-induced growth method can reduce the optical loss and prevent the phosphor from being attacked by moisture.The experimental results show that the amount of saturated solution determines the growth mode of seed-induced deposition.With the increase of the amount,the growth mode gradually changes from layer-layer to layer-island.By optimizing the experimental conditions,the optimal treatment time is 40 minutes,take 1000 mL of saturated solution as standard,the volume of saturated solution is 600 mL,and the number of depositions is one.After aging for 12 days under simulated conditions of 150?high temperature and 100%humidity,the luminous intensity of the red light emitting LED device encapsulated by K₂SiF₆:Mn⁴⁺sample treated with 400 mL saturated solution?T-KSFM?is 90.9%of the initial intensity,the red light emitting LED device encapsulated by T-KSFM sample treated with 600 mL of saturated solution still has93.92%of the initial intensity.White light emitting diode?WLED?is produced by packaging T-KSFM red phosphor,commercial?-sialon:Eu²⁺green phosphor and InGaN blue LED chip.At a drive current of 20 mA,the WLED device produces white light emission with a relative color temperature?CCT?of 7934 K and a lumen efficiency of 97.92 lm/W.The color coordinate in the CIE 1931 color coordinate space is?0.2932,0.3139?,and the color gamut space is 117.6%of the color gamut value of the National Television Standards Committee?NTSC?.?2?Unlike the straight-forward preventive strategies,a reverse strategy“Good comes from bad”was successfully developed to maintain the luminous properties of Mn⁴⁺doped fluoride phosphors and enhance the moisture resistance at the same time.After treatment with an oxalic acid solution as restoration modifier,the emission intensity of the almost completely degraded K₂SiF₆:Mn⁴⁺?D-KSFM?phosphor can be restored to 103.68%of the original K₂SiF₆:Mn⁴⁺red phosphor?O-KSFM?without any treatment,and the moisture resistance is remarkably improved.The restored K₂SiF₆:Mn⁴⁺?R-KSFM?maintains approximately 65%of its initial relative emission intensity after immersing in deionized water for 300 min,while the reference commercial K₂SiF₆:Mn⁴⁺with a protective coating?C-KSFM?is only 32%.As a proof of general applicability,this strategy was also conducted to K₂TiF₆:Mn⁴⁺phosphor,which is less moisture-stable than K₂SiF₆:Mn⁴⁺.The luminescence intensity of the degraded K₂TiF₆:Mn⁴⁺?D-KTFM?phosphor can be restored to 162.59%of original level of the K₂TiF₆:Mn⁴⁺synthesized through a cation exchange approach without any treatment?O-KTFM?.The emission intensity of the restored K₂TiF₆:Mn⁴⁺?R-KTFM?phosphor retains 58%of its initial emission intensity after soaking in deionized water for 300 min.Finally,the R-KSFM phosphors were packaged into white light-emitting diodes with blue InGaN chips and Y₃Al₅O₁₂:Ce³⁺yellow phosphors.The WLEDs display excellent color rendition with higher color rendering index,lower color temperature?WLED-?:R_a=83.6,R₉=57.3,3743 K,?_l=199.68lm/W;WLED-?:R_a=90.4,R₉=94.2,2892 K,?_l=183.3 1m/W?.The above results show that the reverse strategy can be applied in those phosphor materials with poor moisture resistance to restore luminescence properties and improve moisture resistance without excessively care about the deterioration during the production,storage and transportation.