荧光粉/SiO_(2)荧光膜用于高显指激光照明

Phosphor/silica Phosphor Films as a Promising Color Converter for White Laser Lighting with Superior Color Rendering

利用“蓝光激光+无机荧光体”的方式产生白光是当前激光照明的主流技术,具有结构简单、成本低等优势。但现有的无机荧光体光谱中缺乏青绿光和红光成分,导致激光照明的显色指数偏低。本工作通过引入电荷补偿剂Na^(+)的方式,制备出高效的蓝绿色Ca_(3)Sc_(2)Si_(3)O_(12):Ce^(3+),Na^(+)荧光粉,其内/外量子效率分别达到86%和55%;然后结合商用CaAlSiN_(3):Eu^(2+)红粉,以二氧化硅溶胶为无机黏结剂,在蓝宝石衬底上低温制备出高效的复合荧光膜。该荧光膜具有良好的热稳定性,200℃时其荧光强度仍保持在常温下的84%;荧光膜中绿光、黄光、红光成分均匀分布,其半高宽达176 nm;在蓝光激光激发下产生647 lm的白光,光效122 lm/W,光源的显色指数88。这些结果表明荧光粉/SiO_(2)复合荧光膜在高显色激光照明中有广阔的应用前景。

Introduction Laser-driven white lighting has received much attention due to its high brightness,high efficiency,and compact size.Blue laser active inorganic color converter technology is a commonly used method to produce white laser lighting due to its cost-effectiveness and simple structure.However,the existing laser lighting endures a low color rendering index(CRI)because of insufficient cyan-green and red light components in the spectra of existing color converters.Therefore,there is a demand for the development of color converters with intense cyan-green and red emission to improve the optical performance of laser lighting.Methods(Ca_(0.98–x)Na_(x)Ce_(0.02))_(3)Sc_(2)Si_(3)O_(12)(x=0,0.02,0.04,0.06,0.08)(CSS)phosphors were synthesized by a solid-state reaction method.The prepared CSS phosphors were then blended with commercial CaAlSiN_3:Eu~(2+)(CASN)phosphors at different weigh ratios(abbreviated as R/G),which were chosen to be 1/8,1/12 and 1/20.An inorganic binder used was commercially available silica colloidal particles,while an organic binder was polyvinyl pyrrolidone(PVP).Firstly,phosphors,PVP and silica colloidal particles were prepared by thoroughly mixing at a mass ratio of 150:50:1.The resulting slurries were coated on the sapphire substrates via blade coating.Finally,the dried samples were sintered in a muffle furnace at 600℃ for 20 min to remove the organic residues.Results and discussion The CSS host has a cubic Garnet-type structure with the Iaˉ3d space group.Na^(+)ions are introduced into the CSS host to function as a charge compensator.This enables the elimination of the impurity phases of phosphors.Under the excitation of blue light at 450 nm,the CSS phosphors emit a broadband cyan-green light with a peak at 507 nm.As Na^(+)content increases,the emission intensity of CSS phosphors gradually increases due to the enhanced absorption efficiency(AE)and internal quantum efficiency(IQE).As x=0.06,the emission intensity reaches its maximum,which is corresponding to internal/external quantum efficiencies(IQE/EQE)of 86% and 55%,respectively.Dense CSS films were produced using colloidal silica.Clearly,the film is composed of tightly packed phosphors and the gaps between phosphor particles are also filled with SiO_(2).The film is bonded to the substrate tightly,which can be ascribed to the adhesion function of the colloidal SiO_(2).The surface of the film is sufficiently smooth without polishing,and its thickness is 135μm.The SiO_(2)colloidal particles serve as an effective inorganic binder,a filler of gaps and a protective coating.The excitation and emission spectra,decay curves and quantum efficiency of the CSS film are similar to those of the related CSS phosphors.The unimpaired luminescence properties of the film indicate that sintering does not impair the intactness of CSS phosphors.The CSS film displays a thermal quenching at evaluated temperature,and the decrease of the integrated emission intensity of CSS film aligns with that of CSS phosphors,retaining 86%of its initial value at 200℃.When the incident laser power increases from 0.3 W to 5.30 W,the emission intensity of the film increases monotonously.However,when the laser power further increases to6.20 W,the emission intensity of the film decreases sharply and a luminous saturation appears.The maximum luminous flux of717 lm is achieved at an incident laser power of 5.30 W,and the corresponding luminous efficacy is 135 lm/W.Although the CSS film exhibits a high thermal stability and a high luminous efficacy,the CRI of this phosphor-converted white light is 57 due to the deficiency of red light components.To improve the CRI,a composite film comprising CASN and CSS phosphors was fabricated.When the mass ratio of CSS and CASN phosphors is 1/12,the spectral analysis of the composite film reveals a uniform distribution of cyan-green,yellow and red light components,with a half-height width of 176 nm.Also,when excited by 5.3 W blue laser,the composite film emits a white light with a high luminous flux of 647 lm,a luminous efficacy of122 lm/W and a CRI of 88.Conclusions Highly efficient cyan-green CSS phosphors with an IQE/EQE of up to 86%/55% were prepared via introducing charge compensatory additives Na^(+).A composite phosphor film was developed on thermally conductive sapphire substrates using silica colloidal particles as an inorganic binder via combining the prepared cyan-green CSS and commercial red CaAlSiN_(3):Eu^(2+)phosphors.The phosphor film exhibited a superior thermal stability and it maintained 84%of its room-temperature luminescence intensity even at 200℃.The spectral analysis of the film showed an even distribution of cyan-green,yellow and red light components,with a half-height width of 176 nm.Under 5.3 W blue laser excitation,the composite film emitted a white light with a high luminous flux of 647 lm,a luminous efficacy of 122 lm/W and a CRI of 88.These results indicated that the composite phosphor film could have a promising potential for application in high-brightness laser lighting with superior color rendering.