Synthesis And Luminescence Spectra Properties Of Red Phosphors For Warm White LED

White light emitting diode as a new generation of light source have been widely concerned due to their excellent properties such as small volume,high lighting efficiency,and environmental friendliness.Recently,Mn⁴⁺doped fluoride red phosphors have become the research focus.They can gradually replace the traditional commercial Eu²⁺/Eu³⁺doped oxide/nitride red phosphors.Mn⁴⁺belongs to transition metal ions with outer 3d³ electronic configuration.The novel Mn⁴⁺doped fluoride phosphors can exhibit the broad excitation bands in the blue light region and show the red emission under blue light excitation.This dissertation is devoted to the synthesis of novel Mn⁴⁺activated fluorides red phosphors and the application in the warm white LED.The main research works are as follows.A series of Mn⁴⁺activated K₂NaAlF₆ red phosphors were synthesized via a hydrothermal route.The influence of the molar ratio of KF to NaF,reaction temperature and reaction time on the crystal structure and luminescence properties were investigated in detail.The luminescence spectra demonstrate that two intense excitation bands are located at the near-UV and blue region.The phosphor can emit an intense red light upon 460 nm excitation.The thermal stability of the samples was also evaluated.The white LED fabricated with the as-prepared red phosphor exhibits a low color temperature of 4310 K,higher color rendering index of 78.7 and luminous efficacy of 60.22 lm W^-1.The results show that K₂NaAlF₆:Mn⁴⁺can effectively improve color rendering index and decrease color temperature of LEDs.A series of red phosphors based on the subsitution of Mn⁴⁺for Ga³⁺in the lattice of K₂LiGaF₆ were synthesized via a co-precipitation method.The effects of different reaction materials,reaction solvents and surfactants CTAB on the crystal structure,morphology and luminescence properties of the phosphor were investigated.In addition,concentration quenching and thermal quenching were also discussed in detail.The white light-emitting diodes?WLEDs?fabricated with red phosphor K₂LiGaF₆:Mn⁴⁺exhibit good performance that possesses a colour rendering index?R_a=79.6?,a low colour temperature?4378 K?and luminous efficacy of 109.91 lm W^-1.The results show that the K₂LiGaF₆:Mn⁴⁺phosphor can be used as the red component to achieve the warm white light of LEDs.A novel Mn⁴⁺doped narrow-band red phosphors,M₂NaInF₆:Mn⁴⁺?M=K and NH₄?,have been designed and synthesized via a co-precipitation method.To verity the crystal structure and morphology of M₂NaInF₆:Mn⁴⁺,the as-prepared samples were characterized by X-ray diffraction and scanning electron microscopy.The influecnes of different reaction time and sodium materials on the luminescent properties of phosphor K₂NaInF₆:Mn⁴⁺were discussed.The luminescence spectra exhibit that the two phosphors K₂NaInF₆:Mn⁴⁺and?NH₄?₂NaInF₆:Mn⁴⁺can emit red emission under blue light excitation.The fabricated WLED with color rendering index 83.4 and low color temperature 4444 K is attained by adding the prepared red phosphor K₂NaInF₆:Mn⁴⁺.These results show that K₂NaInF₆:Mn⁴⁺and?NH₄?₂NaInF₆:Mn⁴⁺have potential applications in warm white LEDs.