Study On The Spectral Regulation Of Mn⁴⁺ Doped Fluoride Red Phosphors

With the further pursuit of lighting quality,white LEDs have developed from the simple pursuit of efficiency to a brighter and more vivid direction.Mn⁴⁺doped fluoride red phosphors cannot meet the requirements of high luminous efficiency and wide color gamut at the same time.Usually,the 630 nm band emitted by the fluoride red phosphor is located at the edge of the human eye sensitive area,and the matching degree with the human eye sensitive area is not high,so the spectrum needs to be modulated in the direction of short-wave.At the same time,the x-coordinate value of the narrow-band red light with the strongest emission peak at 630 nm is usually less than 0.7 in the chromaticity coordinate,which restricts the further broadening of the color gamut of the packaged white LED display,and it also needs to be modulated to the long-wave band.However,Mn⁴⁺doped fluoride red phosphors are limited by the parity forbidden transition emission of Mn⁴⁺,and it is very difficult to tune their spectra.At the same time,long-wave and short-wave modulation are contradictory and cannot be satisfied at the same time.In this paper,a new type of Mn⁴⁺doped fluoride red phosphor was designed and synthesized.By selecting Mn⁴⁺non-equivalent doped fluoride matrix,the local environment symmetry of Mn⁴⁺was reduced and its ZPL emission was enhanced.At the same time,the reduction of symmetry splits its energy level,and the high covalent nature of the matrix enhances the electron diffusion effect,which reduces the ²E_gemission energy level and redshifts the spectrum.The fluoride red phosphor with long-wavelength phonon sidebands and strong ZPL emission far exceeding the vibration peak was successfully obtained.In addition,the effect of different structures on the luminescence properties of Mn⁴⁺was investigated by changing the structure of the fluoride in the same system to produce a phase transition.The tuning effect of the fluoride structure on the spectrum was described,which provided a reference for obtaining fluoride red phosphors with strong ZPL emission and long-wavelength phonon sideband.The main research contents are as follows:（1）A novel fluoride red phosphor Cs₂NaGaF₆:Mn⁴⁺was successfully prepared by a simple two-step co-precipitation method at room temperature.The phosphor has a strong ZPL emission at 627 nm,which successfully improves the matching degree between the spectrum and the human eye sensitive area.At the same time,the Cs₂NaGaF₆:Mn⁴⁺spectrum shows a6.5 nm red shift and a long-wavelength phonon sideband at 636.5 nm,and the color coordinates（0.7026,0.2910）with x value greater than 0.7 are obtained.In addition,in order to show the superiority of its spectrum,the phosphor was encapsulated into WLED1 for lighting and WLED2 for display.WLED1 has a lumen efficiency of 115.7 lm/W,a CCT of3390 K,a color rendering index of Ra of 92.5,and a chromaticity coordinate of（0.4110,0.3922）.The color coordinates of the encapsulated WLED2 are（0.3149,0.3262）,the color gamut is 118.4%of the National Television System Committee（NTSC）value,and the lumen efficiency is 81.7 lm/W.（2）For Mn⁴⁺doped fluoride spectral tuning difficulties,the cubic phase K₂LiAlF₆:Mn⁴⁺was selected,and Rb ions were introduced to change its structure.The red phosphors of RbKLiAlF₆:Mn⁴⁺and Rb₂LiAlF₆:Mn⁴⁺with rhombohedral phase were successfully prepared.The effects of different structures on luminescence were studied,and the spectral tuning of structure and phase transition was successfully realized.The ZPL emission of K₂LiAlF₆:Mn⁴⁺is very weak,and the ZPL emission of RbKLiAlF₆:Mn⁴⁺and Rb₂LiAlF₆:Mn⁴⁺after structural transformation is greatly enhanced.At the same time,a spectral red shift of about 6 nm is generated,and long-wavelength phonon sidebands are realized at about 636.5 nm and 637 nm,respectively.The luminous efficiency of WLED3 encapsulated by RbKLiAlF₆:Mn⁴⁺is 81.25lm/W,the color coordinate is（0.3019,0.3262）,the color rendering index is 80.6,and the display color gamut is 117.5%of the NTSC value;the WLED4 encapsulated by Rb₂LiAlF₆:Mn⁴⁺has a lumen efficiency of 98.4 lm/W,a color coordinate of（0.3019,0.3262）,a color rendering index of 83.3,and a display gamut of 117.9%of NTSC.