溴氧化物上转换荧光粉及白光LED用硅酸盐荧光粉的性质研究
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摘要
由于稀土离子独特的电子层结构使得稀土离子掺杂的发光材料具有其它发光材料所不具有的许多优异性能。稀土发光材料具有发光亮度高、寿命长、无辐射污染等优异性能特点,一直是国内外发光材料的研究热点。其中上转换发光材料在三维立体显示、红外辐射探测、商标激光防伪等领域具有广泛应用。另外随着白光LED制备技术的不断发展及其应用领域的不断扩展,LED用白光荧光粉的性能和制备的研究越来越受到人们的重视,尤其是可被紫外光激发的稀土激活碱土硅酸盐白光荧光粉。本论文的主体分为两个部分,第一部分是关于稀土离子掺杂的溴氧化物荧光粉的上转换发光性质的研究；另一部分是白光LED用Sr2Si04:Eu2-荧光粉的研究。
第一章概述了上转换发光的研究进展和上转换发光理论。
第二章用高温固相法合成了纯相正交晶系Gd3O4Br:Er3+上转换荧光粉,通过X射线衍射、场发射扫描电子显微镜、拉曼光谱和傅立叶变换红外光谱研究了其结构特性。结果表明Gd3O4Br声子能量低,暗示了Gd3O4Br:Er3+具有高的发光效率。在980 nm激光激发下,观测到Er3+掺杂的Gd3O4Br样品强的绿色(514-582 nm)和红色(645-692nm)上转换发光。Gd3O4Br:Er3+(0.1%)样品在泵浦功率为1mW(980 nm)激光的激发下,肉眼明显可见强的绿光发射,表明此荧光粉可以作为上转换荧光粉。
第三章通过高温固相法合成了纯相四方晶系GdOBr:Er3+上转换荧光粉,通过X射线衍射、拉曼光谱和上转换光谱研究了其结构特性和光学性质。拉曼光谱证明了正方晶系的GdOBr具有低的声子能量,暗示了GdOBr:Er3+具有高的上转换发光效率。在980 nm和785 nm激光激发下,分别测量了Er3+掺杂的GdOBr样品强的绿色(514-582 nm)和弱的红色(645-692 nm)上转换发光。通过上转换发光峰的强度对泵浦激光功率的依赖关系研究了上转换发光机制,结果表明上转换发光是激发态吸收过程。值得关注的是GdOBr:Er3+(1%)样品在泵浦功率为1mW(980 nm)激光的激发下,肉眼明显可以看到很强的绿光发射,表明GdOBr：Er3+荧光粉很适合作为上转换荧光粉。
第四章介绍了在白光LED用荧光粉的工作。在还原气氛下采用以NH4F为助熔剂的高温固相反应法合成了白光LED用Sr2SiO4:Eu2+荧光粉,详细地研究了NH4F对Sr2SiO4:Eu2+荧光粉的结构和发光性质的影响。XRD结果表明,加入适量的NH4F,在1100℃高温下生成的Sr2SiO4:Eu2+为纯相单斜晶系β-Sr2SiO4。当NH4F添加量为6wt%时,Sr2SiO4:Eu2+荧光粉的荧光最强。其发射光谱由两个谱带组成,峰值分别位于474nm和540nm处,归结为Sr2SiO4晶体中占据两种不同Sr格位的Eu2+离子的5d→4f跃迁发射。此外比较了不同种类的助熔剂对Sr2SiO4:Eu2+的发光性质的影响,用NH4F作为助熔剂对Sr2SiO4:Eu2+荧光粉的荧光增强效果明显优于NH4Cl和Li2CO3。研究结果表明用NH4F作为助熔剂合成的Sr2SiO4:Eu2+是一种很好的近紫外芯片激发的白光LED用荧光粉。
第五章对本论文的主要工作进行了总结。
Because of the special electronic structure of rare earth ions (REI), the REI-doped luminescent materials have been proved to be outstanding luminescent materials than other type materials. Owning to their high brightness, long lifetime and non-radiation substance, more attention has been paid to the investigations of REI activated luminescent material. For examples, upconversion materials show extensively applications in three-dimensional displays, infrared radiation detectors, laser anti-counterfeiting brands and so on. The investigation on the fabrication and luminescent properties of white LED (WLED) phosphor, such as REI activated alkaline earth silicate phosphor, has aroused scientists' interest due to the development of elaboration technology of WLED and the extension of applied fields. The thesis contains two parts:(A) upconversion in REI doped Oxybromide-based phosphors, and (B) investigation on Sr2SiO4:Eu2+ WLED phosphors.
In Chapter 1, the research progress and the upconversion mechanisms of upconversion phosphors were reviewed.
In Chapter 2, pure orthorhombic Gd3O4Br:Er3+ upconversion phosphors were synthesized by a solid-state reaction method and the structural properties of Gd3O4Br:Er3+ were investigated by X-ray diffraction, field emission scanning electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The results show that Gd3O4Br has low phonon cutoff energy, indicating that Gd3O4Br:Er3+ may have high luminescent efficiency. Intense green (514-582nm) and strong red (645-692nm) upconverted luminescence of Gd3O4Br:Er3+ were observed under 980 nm laser excitation. The bright green emission is visible to the naked eyes even for 1 mW of the pump power (980 nm) for Gd3O4Br:Er3+ (0.1%) samples, indicating that Gd3O4Br:Er3+ may be used as upconversion phosphors.
In Chapter 3, pure and Er3+ doped GdOBr phosphors were synthesized by a simple solid-state reaction method. X-ray diffraction, Raman spectroscopy and photoluminscent spectroscopy were used to characterize the structural and photoluminscent properties of GdOBr:Er3+. Raman spectra show that tetragonal GdOBr has low phonon energy, indicating that GdOBr:Er3+ may have high upconversion efficiency. Under 980 nm and (or) 785 nm laser excitation, GdOBr:Er3+ samples present strong green (2H11/2,4S3/2→4I15/2) and red (4F9/2→4I15/2) upconverted emissions. The upconversion mechanisms were studied in detail through laser power dependence and excited state absorption process is discussed as the possible upconversion mechanisms. More interesting, the bright green upconverted emission is visible to the naked eyes for GdOBr:Er3+(1%) samples even excited by 1 mW 980 nm laser. Such phenomenon indicates that GdOBr:Er3+ may be used as upconversion phosphors.
In Chapter 4, the investigation on Sr2SiO4:Eu2+ based white LED phosphors is introduced briefly. Sr2SiO4:Eu2+ phosphors were prepared by a conventional solid-state reaction method using NH4F as a flux. The effect of NH4F flux on the structural and luminescent properties of Sr2Si04:Eu2+ was investigated in detail. X-ray diffraction (XRD) results showed that pure monoclinicβ-Sr2SiO4 phase can be elaborated at low annealing temperature (1100℃) by adding appropriate amount of NH4F. The Sr2Si04:Eu2+ phosphors show two emission spectra peaked at 540 and 474 nm originated from the 5d-4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. The intensities of Eu2+ emissions increased with increasing NH4F amount up to 6 wt%. By compared NH4F flux with other fluxes used in preparation of Sr2Si04:Eu2+ phosphors, it is found that NH4F flux is more superior to NH4Cl and Li2CO3 flux. Our investigation indicates that Sr2SiO4:Eu2+ is a good light-conversion phosphor candidate for near-UV chip and NH4F is a good flux for Sr2SiO4:Eu2+.
In Chapter 5, the conclusions of the thesis were summarized.
第一章概述了上转换发光的研究进展和上转换发光理论。
第二章用高温固相法合成了纯相正交晶系Gd3O4Br:Er3+上转换荧光粉,通过X射线衍射、场发射扫描电子显微镜、拉曼光谱和傅立叶变换红外光谱研究了其结构特性。结果表明Gd3O4Br声子能量低,暗示了Gd3O4Br:Er3+具有高的发光效率。在980 nm激光激发下,观测到Er3+掺杂的Gd3O4Br样品强的绿色(514-582 nm)和红色(645-692nm)上转换发光。Gd3O4Br:Er3+(0.1%)样品在泵浦功率为1mW(980 nm)激光的激发下,肉眼明显可见强的绿光发射,表明此荧光粉可以作为上转换荧光粉。
第三章通过高温固相法合成了纯相四方晶系GdOBr:Er3+上转换荧光粉,通过X射线衍射、拉曼光谱和上转换光谱研究了其结构特性和光学性质。拉曼光谱证明了正方晶系的GdOBr具有低的声子能量,暗示了GdOBr:Er3+具有高的上转换发光效率。在980 nm和785 nm激光激发下,分别测量了Er3+掺杂的GdOBr样品强的绿色(514-582 nm)和弱的红色(645-692 nm)上转换发光。通过上转换发光峰的强度对泵浦激光功率的依赖关系研究了上转换发光机制,结果表明上转换发光是激发态吸收过程。值得关注的是GdOBr:Er3+(1%)样品在泵浦功率为1mW(980 nm)激光的激发下,肉眼明显可以看到很强的绿光发射,表明GdOBr：Er3+荧光粉很适合作为上转换荧光粉。
第四章介绍了在白光LED用荧光粉的工作。在还原气氛下采用以NH4F为助熔剂的高温固相反应法合成了白光LED用Sr2SiO4:Eu2+荧光粉,详细地研究了NH4F对Sr2SiO4:Eu2+荧光粉的结构和发光性质的影响。XRD结果表明,加入适量的NH4F,在1100℃高温下生成的Sr2SiO4:Eu2+为纯相单斜晶系β-Sr2SiO4。当NH4F添加量为6wt%时,Sr2SiO4:Eu2+荧光粉的荧光最强。其发射光谱由两个谱带组成,峰值分别位于474nm和540nm处,归结为Sr2SiO4晶体中占据两种不同Sr格位的Eu2+离子的5d→4f跃迁发射。此外比较了不同种类的助熔剂对Sr2SiO4:Eu2+的发光性质的影响,用NH4F作为助熔剂对Sr2SiO4:Eu2+荧光粉的荧光增强效果明显优于NH4Cl和Li2CO3。研究结果表明用NH4F作为助熔剂合成的Sr2SiO4:Eu2+是一种很好的近紫外芯片激发的白光LED用荧光粉。
第五章对本论文的主要工作进行了总结。
Because of the special electronic structure of rare earth ions (REI), the REI-doped luminescent materials have been proved to be outstanding luminescent materials than other type materials. Owning to their high brightness, long lifetime and non-radiation substance, more attention has been paid to the investigations of REI activated luminescent material. For examples, upconversion materials show extensively applications in three-dimensional displays, infrared radiation detectors, laser anti-counterfeiting brands and so on. The investigation on the fabrication and luminescent properties of white LED (WLED) phosphor, such as REI activated alkaline earth silicate phosphor, has aroused scientists' interest due to the development of elaboration technology of WLED and the extension of applied fields. The thesis contains two parts:(A) upconversion in REI doped Oxybromide-based phosphors, and (B) investigation on Sr2SiO4:Eu2+ WLED phosphors.
In Chapter 1, the research progress and the upconversion mechanisms of upconversion phosphors were reviewed.
In Chapter 2, pure orthorhombic Gd3O4Br:Er3+ upconversion phosphors were synthesized by a solid-state reaction method and the structural properties of Gd3O4Br:Er3+ were investigated by X-ray diffraction, field emission scanning electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The results show that Gd3O4Br has low phonon cutoff energy, indicating that Gd3O4Br:Er3+ may have high luminescent efficiency. Intense green (514-582nm) and strong red (645-692nm) upconverted luminescence of Gd3O4Br:Er3+ were observed under 980 nm laser excitation. The bright green emission is visible to the naked eyes even for 1 mW of the pump power (980 nm) for Gd3O4Br:Er3+ (0.1%) samples, indicating that Gd3O4Br:Er3+ may be used as upconversion phosphors.
In Chapter 3, pure and Er3+ doped GdOBr phosphors were synthesized by a simple solid-state reaction method. X-ray diffraction, Raman spectroscopy and photoluminscent spectroscopy were used to characterize the structural and photoluminscent properties of GdOBr:Er3+. Raman spectra show that tetragonal GdOBr has low phonon energy, indicating that GdOBr:Er3+ may have high upconversion efficiency. Under 980 nm and (or) 785 nm laser excitation, GdOBr:Er3+ samples present strong green (2H11/2,4S3/2→4I15/2) and red (4F9/2→4I15/2) upconverted emissions. The upconversion mechanisms were studied in detail through laser power dependence and excited state absorption process is discussed as the possible upconversion mechanisms. More interesting, the bright green upconverted emission is visible to the naked eyes for GdOBr:Er3+(1%) samples even excited by 1 mW 980 nm laser. Such phenomenon indicates that GdOBr:Er3+ may be used as upconversion phosphors.
In Chapter 4, the investigation on Sr2SiO4:Eu2+ based white LED phosphors is introduced briefly. Sr2SiO4:Eu2+ phosphors were prepared by a conventional solid-state reaction method using NH4F as a flux. The effect of NH4F flux on the structural and luminescent properties of Sr2Si04:Eu2+ was investigated in detail. X-ray diffraction (XRD) results showed that pure monoclinicβ-Sr2SiO4 phase can be elaborated at low annealing temperature (1100℃) by adding appropriate amount of NH4F. The Sr2Si04:Eu2+ phosphors show two emission spectra peaked at 540 and 474 nm originated from the 5d-4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. The intensities of Eu2+ emissions increased with increasing NH4F amount up to 6 wt%. By compared NH4F flux with other fluxes used in preparation of Sr2Si04:Eu2+ phosphors, it is found that NH4F flux is more superior to NH4Cl and Li2CO3 flux. Our investigation indicates that Sr2SiO4:Eu2+ is a good light-conversion phosphor candidate for near-UV chip and NH4F is a good flux for Sr2SiO4:Eu2+.
In Chapter 5, the conclusions of the thesis were summarized.
引文
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