Study Of Up/Down-conversion Fluorescent Nanomaterial With SiO₂ Coated-rare-earth Nanoparticles On Si Nanowires

Fluorescent nanomaterials not only retain the advantage of nanomaterials but they have their unique optical properties.They have been widely adopted in a wide variety of applications including immunofluorescence analysis,ion recognition,protein activity assay,fluorescence labeling,optical imaging,and medical diagnosis.Therefore,it is of great significance to carry out the research on the preparation,structure characterization,luminescence properties and stability of fluorescent nanomaterials.This paper presents research work on the preparation,luminescence properties and applications of SiO₂ coated rare earth(Eu³⁺,Tb³⁺,Ce³⁺,Er³⁺ and Yb³⁺,etc.)nanoparticles on the surface of Si nanowires.First,the high density and large area Si nanowires?SiNWs?were grown from the Si?100?surface by using metal?Au/Au-Al?as catalyst based on the solid-liquid-solid growth mechanism.Then,the SiO₂ coated rare earth nanoparticles were formed on the surface of the nanowires by mixed the rare earth oxides?Eu₂O₃,Tb₄O₇,CeO₂,Y₂O₃,Er₂O₃ and Yb₂O₃?and Si nanowires under high temperature treatment.Which realized up/down-conversion fluorescent emission.Next,the structure and luminescence properties of Si nanowire fluorescent nanomaterials under different process parameters?e.g.heat treatment temperature,time and nitrogen flow,etc.?and rare earth doped concentration were investigated using transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,X-ray diffraction?XRD?and fluorescence spectrometer device.Our major research results are summarized as follows:?1?The synthesis of down-conversion fluorescent nanomaterial Si NWs:Eu³⁺(Tb³⁺ and Ce³⁺)under the temperature of 1000-1200? and N₂ gas flow rate of 1000 sccm with Eu₂O₃,Tb₄O₇ and CeO₂ powder as the impurity source.TEM measurement results show that there are a large number of SiO₂ with thickness is 5-30 nm coating rare earth nanoparticles on SiNWs surface.Si nanowire fluorescent nanomaterial has significant application value due to the important properties of SiO₂ including non-toxic,pollution-free,excellent stability and surface easy modification.At room temperature,the samples realized the red,green and blue optical emission.The results demonstrate that the Eu³⁺-doped SiNWs have a strong red luminescencent with an emission peak position at 619nm?⁵D₀?⁷F₂?and four emission band of 576 nm?⁵D₀ ?⁷F₀?,596nm?⁵D₀ ?7F1?,658 nm?⁵D₀?7F3?and 708nm?⁵D₀?7F4?were observed as well.Also,the Tb³⁺-doped SiNWs have a strong green luminescencent with an emission peak position at 554nm?5D4?7F5?and three emission band of 494 nm?5D4?7F6?,593nm?5D4?7F4?and 628nm?5D4?7F3?were observed,with the fluorescence quantum efficiency as 60.66%.Additionally,the Ce³⁺-doped SiNWs have a strong blue luminescencent with a wide emission peak position at 405nm(5D?²F_5/2)and the full width at half maxim?FWHM?is 36.7nm.The fluorescence quantum efficiency is 90.57%.Finally,the experimental test shows that,the structural materials are suitable as a fluorescent because they have good properties such as time,temperature,acid and alkali,anti light bleaching stability and good water solubility and dispersion.?2?To improve the red emission intensity of Eu³⁺,the fluorescent nanomaterial SiNWs: Eu³⁺,Y3+ was prepared by Y₂O₃ and Eu₂O₃ powders co-doped SiNWs at high temperature.The results show that as the ratio of Y3+ is 2.5%,the intensity of red emission of Eu³⁺ is higher than that of undoped Y3+,and the strength is increased by approximately 110%.Therefore,the optimization of Y3+/Eu³⁺ ratio can effectively improve the Eu³⁺ red emission intensity.At the same time,the FWHM of 619 nm emission peak is reduced from 10.2nm to 7.2nm and thus it can improve the sensitivity and resolution of nanomaterials for fluorescent labeling.?3?To improve the green emission intensity of Tb³⁺,the fluorescent nanomaterial SiNWs: Tb³⁺,Ce³⁺ was prepared by Tb₄O₇ and CeO₂ powders co-doped Si nanowires.The emission spectrum of Ce³⁺ and the excitation spectrum of Tb³⁺ have some overlapping areas,which makes the energy transfer possible from Ce³⁺ to Tb³⁺.When the total doping amount is constant,the emission intensity of the characteristic peak of Tb³⁺ grows slowly and then drops with the increase of Ce³⁺ doping concentration and decrease of Tb³⁺ concentration.When the ratio of Ce³⁺ doping is 15%,the strength of green light emission is increased by approximately 250%.At the same time,the material can be realized from the "blue-green to yellow-green" light emission under different excitation light,and hence it can effectively increase its application range.?4?The upconversion fluorescent nanomaterial SiNWs:Er³⁺,Yb³⁺ was realized by Yb₂O₃ and Er₂O₃ powders co-doped Si nanowires with the temperature as 1200?,doping time as 60 min,the N₂ flow rate as 1000 sccm,and the ratio of Yb³⁺:Er³⁺ as 2:1.The SiNWs:Er³⁺,Yb³⁺ produced green and red emission band of Er³⁺ with 520-570nm?2H11/2? 4S3/2?and 640-680nm?4F9/2?4I15/2?using laser excitation with a wavelength of 980 nm.The Yb³⁺ as a sensitizer absorbed the infrared light of near 980 nm and then transferred energy to the luminescence center of Er³⁺.?5?The CD44 protein were fluorescently labeled by the upconversion of SiNWs:Er³⁺,Yb³⁺.First,silane coupling agent is used to enable SiO₂ to carry the carboxyl;Second,SiO₂ coated layer of carboxyl were activated through the EDC and then crosslinked with sheep anti mouse IgG;Finally,cross-linking with the mouse anti human CD44 and fluorescence color were carried out.The SiNWs:Er³⁺,Yb³⁺ shows good brightness and long term stability.