Preparation And Characterization Of Green-emitting Phosphor Ba₂Si₃O₈:Eu²⁺ For White-LEDs

White light-emitting diodes have been considered as the next generation light source because of their advantages such as energy-conservation,environmental protection,high-efficiency and reliability,which provides tremendous economic and social benefits.With the continuous development of near-UV-LED chip technology,it has important research significance and application value to explore novel trichromatic phosphor which can be excited effectively by near ultraviolet LED.In this thesis,research progress of trichromatic phosphor for white LED was summarized.Based on the thermal properties stability and chemical properties stability of the silicate matrix,a novel green phosphor Ba₂Si₃O₈:Eu²⁺ was succussfully synthesized by solid-state reaction and sol-gel method.The formation process, microscopic structure,luminescence properties of the phosphors were studied by DTA, TG,XRD,SEM,TEM,PL measurement,etc.The morphology and luminescent properties of phosphor synthesized by two different technique routes were compared. Furthermore,the morphology of the phosphor was designed with the core-shell structure phosphor SiO₂@Ba₂Si₃O₈:Eu²⁺,whish was synthesized by Pechini sol-gel method followed by post-annealing process using mono-dispersive SiO₂ microspheres as cores and Ba₂Si₃O₈:Eu²⁺ as shells.A novel green phosphor Ba₂Si₃O₈:Eu²⁺ was successfully synthesized by solid-state reaction.With the increase of calcining tempereture,the sample has experienced the phase evolution process from BaSiO₃→Ba₂Si₃O₅.The excitation spectrum of product Ba₂Si₃O₈:Eu²⁺ phosphor is a broad band covered 300nm～450nm with peak center around 370nm,which well-matched with the emission of near-UV-LED chips.On the other hand,the emission spectrum is a single intense broad band centered at 502nm and exhibits intensity green light.The broad emission spectral band could be attributed to the Eu²⁺ activator with classical 4f⁶5d¹-4f⁷ parity allowed transitioncenter.It was revealed that the preparation parameters for phosphors such as calcine temperature,reaction time,flux concentration,activator concentration have great impact on morphologies and luminescent properties of as-prepared phosphors.The optimized parameters for present phosphors were determined as follows:calcine temperature of 1250℃,holding time of 3h,flux concentration of 5wt%and activator concentration of Eu ions be 0.05.The concentration quenching mechanism of Eu ions was supposed to be the dipole-dipole interaction.In the solid-solution matrix of alkaline-earth metal such as Ca²⁺ and Sr²⁺ ions replaced Ba²⁺ in the lattice,the luminescence properties change too.It was found that the Ca²⁺ replacement makes blue-shift in the emission peak and a little amount of Ca²⁺ replacement for Ba²⁺ enhances the emission intensity while access amount of Ca²⁺ replacement reduces the emission intensity.On the contrary,the Sr²⁺ replacement reduces the emission intensity and causes red-shift within the doping level. Furthermore,the sensitization effect of Ce³⁺ ions has been verified and the luminescence intensity of Eu²⁺ emission could significantly enhanced by Ce³⁺ co-doping.The energy transfer process between Ce³⁺ and Eu²⁺ was observed and the optimized concentration of Ce³⁺ ions is 0.04,which could increase the luminescence intensity for almost 8.6 times as much as that of Ce³⁺-free Ba₂Si₃O₈:Eu²⁺ phosphor.It was revealed that the phase evolution process is Ba₂SiO₄→BaSiO₃→Ba₂Si₃O₈ with increasing temperature for sol-gel derived samples.The excitation spectra of the prepared phosphor covers 300nm～450nm with peak center at 370nm,which matches well with the emission spectrum of near-UV-LED chips.The emission spectrum consists of a single intense broad band centered at 502nm and exhibits intensity green light.The broad emission spectral band could be attributed to the Eu²⁺ activator with classical 4f⁶5d¹-4f⁷ parity allowed transition center.Well dispersed phosphor with average particle size around 2～4μm could be obtained by sol-gel method with merits of ball milling process free.However,it was found that the luminescence intensity of sol-gel derived phosphor is weaker than that of solid-state reaction derived phosphor.Core-shell structure phosphor SiO₂@Ba₂Si₃O₈:Eu²⁺ was successfully synthesized by Pechini sol-gel method using size-controllable,low-cost SiO₂ microspheres as cores and Ba₂Si₃O₈:Eu²⁺ phosphor as shells.The XRD,SEM,TEM results indicated that Ba₂Si₃O₈:Eu²⁺ phosphor could be successfully coated on the surface of SiO₂ microspheres.The obtained core-shell structure SiO₂@Ba₂Si₃O₈:Eu²⁺ phosphor has good dispersion state and maintains spherical structural features with particle sizes around 330nm.The phosphor shows broad band covered 300nm～450nm with peak center around 370nm,which matches well with the emission of near-UV-LED chips. Its emission spectrum consisted of a single intense broad band centered at 502nm and exhibits intensity green light.The broad emission band could be attributed to the Eu²⁺ activator with classical 4f⁶5d¹-4f⁷ parity allowed transition center.Furthermore,the luminescence intensity of SiO₂@Ba₂Si₃O₈:Eu²⁺ phosphor could be enhanced by increasing the numbers of coated times.