Cyan And White Luminescence Of Eu-doped Single Matrix Materials For UV-LED

Commercial LED phosphor YAG:Ce presents cool color temperature,low color rendering index（CRI）,color drift and blue damage for long-term lighting due to the lack of red component when excited with blue light,which is not conducive to color reproduction and lighting health.Tri-chromatic fluorescent phosphors excited by near-ultraviolet（NUV）for LED have uniform spectral composition and high CRI,but cyan gap（480-520 nm）still exists in commercial materials,which leads to difficult to achieve the standard of health lighting with high CRI and full-spectra.It is significant to research on new-type cyan fluorescent materials for realizing high CRI and healthy lighting.In this paper,high efficiency emission from red to cold white and cyan were realized in Eu doped single-host-materials under the excitation of UV/NUV,which were prepared by reducing agents in different degrees:1.Red,cold white and cyan emission of Eu²⁺/Eu³⁺doped Ca₂Gd₈（Si O₄）₆O₂phosphors:Ca₂Gd₈（Si O₄）₆O₂phosphors diped with Eu were synthesized by high-temperature solid-phase method.During the process of preparation,Eu³⁺could be partly or all reduced to Eu²⁺by C.Under the excitation of UV/NUV,the red,cold white and cyan emission can be realized in these Ca₂Gd_8-x（Si O₄）₆O₂:x Eu phosphors.When all Eu³⁺is reduced to Eu²⁺,cyan phosphor with FWHM of 153 nm and color coordinate of（0.27,0.36）can be obtained.Fine structure analysis shows that Ca²⁺occupies two different lattice sites of Ca₂Gd₈（Si O₄）₆O₂,namely[Ca O₇]and[Ca O₉]respectively,which induced two different luminescent centers at 470 and 525 nm,so cyan emission can be obtained.In addition,cold white light can be obtained in this material when Eu³⁺partially reduced with color coordinate（0.33,0.31）and CRI 78.2.Red,cold white and cyan emission of Eu²⁺/Eu³⁺doped glasses containing Na YF₄nanocrystals:Eu doped Na YF₄glass-ceramics were prepared by high temperature solid phase melting and quenching method.By adding different amounts of Si₃N₄during the preparation process,Eu³⁺can be reduced to varying degrees until completely reduced,and the Na YF₄glass-ceramics can emit red,cold white and cyan light under the excitation of near-ultraviolet light of 395 nm.When 0.5 mol%Si₃N₄was added,Eu²⁺doped Na YF₄glass-ceramics have the color coordinate of（0.29,0.37）,which can fill the cyan gap,and when 0.05 mol%Si₃N₄was added,a cold white light of Eu³⁺/Eu²⁺co-doped Na YF₄glass-ceramic obtained with the color coordinate of（0.32,0.32）and CRI of 84.In addition,thermal vibration cycle experiments show that these glass ceramics have good thermal stability and can be encapsulated to white light LED devices.