SiNWs:Tb^(3+)的光学稳定性及Si纳米线对其发光特性的影响

The Optical Stability of SiNWs:Tb^(3+)and the Effects of Si Nanowires on Its Luminescent Properties

荧光纳米材料不但具备纳米材料的优势,同时还具有优异的光学性质,被广泛应用于荧光标记、离子识别、荧光免疫分析、光学成像和医学诊断等方面。因此,荧光纳米材料的制备、结构分析和荧光特性等方面的研究备受人们的关注。为了获得发光强度大、荧光量子效率高和制备过程可控的Si基荧光纳米材料,实验进一步研究了Si纳米线对样品发光特性的影响和样品的光学稳定性。首先,基于固-液-固生长机制,在反应温度为1 100℃、 N_2气流量为1 500 sccm、生长时间为15～60 min等工艺条件下,分别以"抛光"和"金字塔"织构表面的单晶Si(100)为衬底,生长出不同长度和分布的Si纳米线;以Au或Au-Al合金膜层作为金属催化剂,生长出密度分别约为10~8和10^(10) cm^(-2)的Si纳米线;然后,利用L4514自动控温管式加热炉,基于高温固相法,在温度为1 100℃、掺杂时间为60 min和N_2气流量为1 000 sccm等工艺条件下,以高纯Tb_4O_7(99.99%)粉末为稀土掺杂剂对不同Si纳米线衬底进行稀土掺杂,制备一系列的荧光纳米材料SiNWs:Tb^(3+)样品;室温下利用Hitachi F-4600型荧光分光光度计,固定激发光波长为243 nm、激发光狭缝为2.5 nm、发射光狭缝为2.5 nm、扫描波长范围为450～650 nm、光电倍增管(photomultiplier lube, PMT)电压为600 V等参数下,测量了不同样品的光致发光特性;最后,实验测试了该荧光纳米材料的光学稳定性,如时间(0～30 d)、温度(300～500 K)、酸碱(pH 1和11)、抗光漂白(0～120 min)等稳定性以及水溶性和分散性。结果显示,在衬底为"金字塔"织构表面上、生长时间为30 min、以Au为金属催化剂等条件下制备的Si纳米线为Tb^(3+)掺杂衬底时, SiNWs:Tb^(3+)的绿光发射强度较大,其发光强峰值位于554 nm,属于能级~5D_4→~7F_5的跃迁,另外在波长为494, 593和628 nm出现了三条发光谱带,它们分别属于能级~5D_4→~7F_6,~5D_4→~7F_4和~5D_4→~7F_3的跃迁。另外,样品展示出了优异的时间、温度、酸碱和抗光漂白等光学稳定性,同时还具有良好的水溶性和分散性。如温度升高到500 K时,光发射强度仅降低了约8.9%左右;抗光漂白能力较强,用波长为365 nm、功率为450 W的紫外光源照射120 min,样品的绿光发射强度无衰减;酸、碱稳定性好,在pH 1的强酸(HCl)溶液中120 min未见衰减,在pH 11的强碱(NaOH)溶液中15 min内衰减较小,随后发光强度出现了缓慢下降的趋势;当60 min后,样品的发光强度变得极其微弱。分析认为,在SiNWs:Tb^(3+)表面有一层SiO_2包覆层,而NaOH溶液容易和SiO_2发生化学反应,随着时间延长SiO_2层被破坏,故样品发光强度降低;样品溶于水中放置30 d未见沉淀物,发光亮度均匀且分散性较好。在研究了制备温度、气体流量和掺杂时间等工艺条件之后,深入研究了Si纳米线自身变化对Tb^(3+)绿光发射的影响。该材料展示出了良好的光学稳定性、水溶性和分散性,使其作为荧光标记物具有一定的应用价值。

Fluorescent nanomaterials not only have the advantages of nanomaterials,but also have excellent optical properties.They are widely used in fluorescent labels,ion recognition,fluorescence immunoassays,optical imaging and medical diagnostics.Therefore,researches on the preparation,structure analysis and fluorescence characteristics of fluorescent nanomaterials have received much attention.In order to obtain Si-based fluorescent nanomaterial with high luminous intensity,high fluorescent quantum efficiency and better controlling of preparation process,the effects of Si nanowires on the luminescence properties and the optical stabilities of the samples were investigated.First,based on the solid-liquid-solid growth mechanism,Si nanowires were grown under the conditions of reaction temperature of 1 100℃,N2 gas flow rate of 1 500 sccm and growth time of 15~60 min.The Si nanowires with different lengths and distributions were grown on single-crystal Si(100)substrates with"polishing"and"pyramid"texture surfaces respectively.And the Si nanowires with density of about 10^8 and 10^10 cm^-2 were grown with Au or Au-Al alloy film as metal catalyst.Then,a series of fluorescent nanometers SiNWs:Tb^3+samples were prepared using L4514 automatic temperature control tube heating furnace based on high-temperature solid-state method under the temperature 1 100℃,doping time 60 min,N2 gas flow rate 1 000 sccm,different Si nanowire substrates and high-purity Tb 4O 7(99.99%)powder as doping agent.Next,at room temperature,the photoluminescence characteristics of different samples were measured by the Hitachi F-4600 fluorescence spectrophotometer with the fixed excitation light wavelength of 243 nm,the excitation light slit of 2.5 nm,the emission light slit of 2.5 nm,the scanning wavelength range of 450~650 nm and the PMT voltage of 600 V.Finally,the optical stabilities of the fluorescent nanomaterial was experimentally tested,such as time stability(0~30 d),temperature stability(300~500 K),acid and alkali stability(pH 1 and pH 11),anti-photobleaching stability(0~120 min),etc.Besides the water solubility and the dispersibility were tested.The results showed that SiNWs:Tb^3+produced strong green light emission with Si nanowires substrate which was prepared with the growth time 30 min,the"pyramid"texture surface and Au as the metal catalyst.The peak of green emission was 554 nm,which belongs to energy level transition 5D4→7F5.At the same time,three bands appeared at wavelengths of 494,593 and 628 nm,which belong to the energy levels transitions 5D4→7F6,5D4→7F4 and 5D4→7F3,respectively.In addition,the sample was shown to have excellent optical stabilities such as time,temperature,acid-base,anti-photobleaching,good water solubility and dispersibility.When the temperature is increased to 500 K,the light emission intensity is reduced by only about 8.9%.The green light luminescence intensity of the sample is not attenuated when irradiated with an UV light source with a wavelength of 365 nm and a power of 450 W for 120 min.In the strong acid solution of pH=1,no attenuation was found in 120 min and the attenuation was less in 15 min in the strong alkaline solution of pH 11.Subsequently,the luminous intensity showed a slow decline,but the luminous intensity of the sample became extremely weak after 60 min.The analysis showed that there is a layer of SiO2 coating on the surface of SiNWs:Tb^3+,and NaOH solution easily reacts with SiO2.As time increases,the SiO2 layer is destroyed,so the luminescence intensity of the sample decreases.There was no deposit found when the sample dissolved in water for 30 days.At the same time,the luminance of solution was uniform.After studying the process conditions such as preparation temperature,gas flow rate and doping time,the influence of Si nanowires on Tb^3+green light emission was studied in depth.The material showed good optical stabilities,water solubility and dispersibility.It has a certain application value as a fluorescent marker.