Synthesis And Investigation Of Solely Doped Single-phase Materials With White Emission For White Light Emitting Diodes

Single-phase solely doped white light emitting phosphors will become a new hot area of research,which can effectively solve the problem of low color rendering index that resulted from the deficiency of red component in YAG:Ce³⁺ phosphor and blue chip system,and the problem of difficult to control the proportion of each phosphor in RGB phosphor and UV chip system.In the paper closely focused on the theme of single-phase solely doped white light emitting,two novel phosphors excited by UV light and activated by Eu²⁺ ions were developed.The results are as follows:A series of single-phase white light Ba₃GdNa?PO₄?₃F: Eu²⁺ phosphors were synthesized by solid-state reactions.The crystal structure of Ba₃GdNa?PO₄?₃F was found to crystallize in a hexagonal crystal system with space group of P6.The Eu²⁺-activated Ba₃GdNa?PO₄?₃F phosphors exhibited broad excitation spectra ranging from 250 to 420 nm,which matched well with the n-UV LED chips.Under the excitation of 365 nm,the emission spectrum almost covered the entire visible region including two emission band peaked at 472 nm and 640 nm.Three different Eu²⁺ emission centers in Ba₃GdNa?PO₄?₃F: Eu²⁺ phosphor were confirmed by their fluorescence decay lifetimes.The CIE value of Ba_2.95GdNa?PO₄?₃F: 0.05Eu²⁺ was calculated to be?0.3283,0.3011?.The influence of fired temperature and holding time were investigated systematically.In addition,the effect of ions substitution on crystal structure and luminescent properties were investigated.Small amount of Ca²⁺ substitution for Ba²⁺ decreased the cell volume and enhanced the emission intensity without changing the CIE obviously.A solid solution was formed with Y³⁺ ions occupying Gd³⁺ ions sites and lead to the emission spectrum shift to red region.The incorporation of Si4+ ions entered into interstitial sites rather than occupied P⁵⁺ ions sites and the introduction of small amount Si⁴⁺ helped to improve thermal stability.The substitution of Cl-ions for F-ions changed the crystal of the host and resulted in the disappeared of red emission peak,and the emission color ranged from white to blue-green.A series of novel single-phase color-tunable phosphor,Eu²⁺-activated Li₄SrCa(Si₂O₄N_8/3): Eu²⁺ phosphor were synthesized via the conventional solid-state reaction method.The crystal structure of Li₄SrCa(Si₂O₄N_8/3)was determined by Reitveld refinement on XRD diffraction data.Li₄SrCa(Si₂O₄N_8/3)crystallizes in an orthorhombic unit cell with space group Pbcm.Under an excitation UV light,the phosphor showed two main emission bands peaking at 430 nm and 578 nm,which corresponds to the Eu²⁺ occupying the ten-coordination Sr sites and six-coordination Ca sites,respectively.The energy transfer existed in different Eu²⁺ emission centers.Under 375 nm excitation,the color hue tuned from blue to yellow,including white light with the increase of Eu²⁺ concentration.When the concentration of Eu²⁺ were 0.03 and 0.04,the CIE were?0.3387,0.3153?and?0.3537,0.3385?,respectively.The phosphor showed very good thermal stability and color stability.A white light-emitting diode was fabricated with Ba_2.95GdNa?PO₄?₃F: 0.05Eu²⁺ phosphor and a 370 nm UV chip.When the applied current was 100 mA,the white LED achieved a CIE of?0.3317,0.3019?with a color-rendering index of 73.9 around the CCT of 6283 K.A white-LED was fabricated with Li₄SrCa_0.97(Si₂O₄N_8/3): 0.03Eu²⁺ phosphor and a 375 nm LED chip.When the applied current was 80 mA,the white LED had a CIE of?0.3568,0.3111?and Ra of 82.5 around the CCT of 3318 K,achieved warm white light.