稀土掺杂氟化物多层核壳纳米晶上转换和量子剪裁的研究

发布时间：2019-05-27 12:40

【摘要】：稀土掺杂材料的特殊光学性质,使其在太阳能电池领域、生物成像、生物传感器等具有广泛的应用。尤其是在太阳能电池领域,稀土掺杂发光材料可以有效地针对两种损失效应,解决太阳能电池转化率低的问题:通过上转换将低于吸光材料带隙宽度的光子转换到其吸收范围内;通过量子剪裁过程将一个高能量的光子剪切成两个或多个低能量的光子,解决紫外高能量光子无法被有效吸收的问题。但是目前,在这方面的研究都集中在块状材料。针对以上问题,本论文设计了稀土氟化物多层核壳结构,实现了低于硅带隙宽度的光子的上转换,实现了紫外光高能量光子的量子剪裁,实现了这两种发光机制在一种纳米晶中的共同作用。分别通过Er~(3+),Ho~(3+),Tm~(3+)三种离子的单掺体系,将硅带隙(1100nm)以下的波段的光子通过上转换过程,转换到硅带隙(1100nm)以内。研究了Er~(3+)单掺体系(1523nm)在三种氟化物掺杂纳米晶基质中的发光性能,结果显示NaYF_4为最佳基质。调节Er~(3+)在NaYF_4基质中的掺杂浓度,当掺杂浓度为10%时其上转换发光最强。通过外延生长方法在三种Er~(3+)单掺杂纳米晶表面分别包覆一层同质惰性壳层,包覆后三种基质核壳结构纳米晶的发光强度较核纳米晶都得到显著增加,其中NaYF_4:10%Er~(3+)@NaYF_4效果最佳,高于其他两种基质核壳结构纳米晶1倍左右,积分球测得其量子产率为3.9%,在目前报道的Er~(3+)单掺体系中,发光强度最高。与Er~(3+)单掺体系相类似,以NaYF_4为基质对Ho~(3+)(1157nm)单掺体系和Tm~(3+)(1213nm)单掺体系进行研究。选择NaYF_4为基质,合成多层核壳结构纳米晶将Er~(3+),Ho~(3+),Tm~(3+)三种离子分别掺杂在不同的壳层中,并在每个活性层之间,引入惰性隔离层阻止掺杂层与掺杂层之间的交叉弛豫。合成了NaYF_4:10%Er~(3+)@NaYF_4@NaYF_4:10%Ho~(3+)@NaYF_4@NaYF_4:1%Tm~(3+)@NaYF_4多层核壳结构纳米晶。相比于无隔离层的NaYF_4:10%Er~(3+)@NaYF_4:10%Ho~(3+)@NaYF_4:1%Tm~(3+)@NaYF_4多层核壳结构纳米晶,以及共掺的NaYF_4:10%Er~(3+),10%Ho~(3+),1%Tm~(3+)@NaYF_4核壳结构纳米晶,在1523nm激光激发下,发光强度分别增强1.9倍和16.7倍;在1157nm激光激发下,发光强度分别增强2.1倍和14.5倍;在1213nm激光激发下,发光强度分别增强1.4倍和6.7倍。在此基础上分别研究Er~(3+),Ho~(3+),Tm~(3+)单掺的上转换发光机理。测试了含有隔离层多层核壳结构纳米晶的激发光谱,其对于硅带隙以下红外波段的响应范围扩大到270nm。以NaYF_4为基质,研究Tb~(3+)-Yb~(3+)掺杂对,Pr~(3+)-Yb~(3+)掺杂对和Er~(3+)单掺杂氟化物纳米晶对紫外光的量子剪裁过程。控制Tb~(3+)掺杂浓度为2%,调节NaYF_4:2%Tb~(3+),x%Yb~(3+)(x=0、20、40、60、80)纳米晶的形貌和尺寸,得到尺寸一致、分散均一的纳米颗粒。发现随着Yb~(3+)掺杂浓度的增加,其量子剪裁发光增强;超过20%后,发光逐渐减弱。通过研究发光强度和激发功率的依附关系,提出量子剪裁机理,通过理论计算,得到量子剪裁效率为183.7%。研究了壳层对NaYF_4:2%Tb~(3+),x%Yb~(3+)(x=0、20、40、60、80)量子剪裁的影响,在惰性壳层包覆下,其量子剪裁的发光全部增强,并且趋势与核纳米颗粒相比有所变化,随着Yb~(3+)掺杂浓度的增加,核壳结构纳米晶发光逐渐增强,Yb~(3+)掺杂浓度为80%时发光最强。通过多层核壳结构同时实现了转换(Er~(3+))和量子剪裁(Tb~(3+)-Yb~(3+))两个过程在一种纳米颗粒中。合成了NaYF_4:10%Er~(3+)@Na Lu F_4@NaYF_4:2%Tb~(3+),20%Yb~(3+)@NaYF_4核壳结构纳米晶,Na Lu F_4作为中间隔离层不但可以有效的减弱两种掺杂壳层中的的交叉弛豫,同时Lu和Y的原子质量差异使其可以通过透射电子显微镜直接观察到多层核壳的结构。采用相对法测量了上转换和量子剪裁过程的量子效率,上转换以NaYF_4:10%Er~(3+)@NaYF_4为标准样,得到量子产率为3.6%左右,量子剪裁以罗丹明6G作为标准样,测出量子剪裁的量子产率为130%左右。
[Abstract]:The special optical property of the rare-earth doped material has wide application in the field of solar cells, biological imaging, biological sensors and the like. in particular in that field of solar cell, the rare-earth-doped luminescent material can effectively solve the problem of low conversion rate of the solar cell aiming at the two loss effect: the photons which are lower than the band-gap width of the light-absorbing material are converted into the absorption range by the up-conversion; By the quantum cutting process, a high-energy photon is cut into two or more photons with low energy, and the problem that the ultraviolet high-energy photon cannot be effectively absorbed can be solved. At present, however, research in this area is focused on the bulk material. In view of the above problems, this paper designs a rare-earth fluoride multi-layer core-shell structure, realizes the up-conversion of photons below the silicon band gap width, realizes the quantum cutting of the high-energy photons of the ultraviolet light, and realizes the common action of the two light-emitting mechanisms in a nano-crystal. In the single-doping system of Er ~ (3 +), Ho ~ (3 +) and Tm ~ (3 +), the photons of the band below the band gap (1100 nm) are converted into the silicon band gap (1100 nm) by the up-conversion process. The light-emitting performance of Er ~ (3 +) single-doping system (1523 nm) in three kinds of fluoride-doped nanocrystalline matrix is studied. The results show that NaYF _ 4 is the best matrix. The doping concentration of Er ~ (3 +) in the NaYF _ 4 matrix is adjusted. When the doping concentration is 10%, the conversion luminescence is the strongest. in that method, a layer of homogeneous inert shell layer is respectively coat on the surface of the three Er-(3 +) single-doped nano-crystal by an epitaxial growth method, and the luminescence intensity of the nano-crystal of the three matrix core-shell structure is obviously increased compared with that of the nuclear nano-crystal, wherein the effect of NaYF _ 4:10% Er-(3 +) @ NaYF _ 4 is the best; The quantum yield was 3.9% higher than that of the other two core-shell structures, and the luminous intensity was the highest in the currently reported Er ~ (3 +) single-doped system. The single-doping system of Ho ~ (3 +) (1157 nm) and Tm ~ (3 +) (1213 nm) single-doping system were studied with NaYF _ 4 as the matrix. When NaYF _ 4 is selected as a matrix, the three ions of Er ~ (3 +), Ho ~ (3 +), Tm ~ (3 +) are respectively doped in different shell layers, and the cross-relaxation between the doped layer and the doped layer is prevented by introducing an inert isolation layer between each active layer. Synthesis of NaYF _ 4:10% Er ~ (3 +) @ NaYF_4@NaYF_4:10% Ho ~ (3 +) @ NaYF_4@NaYF_4:1% Tm ~ (3 +) @ NaYF _ 4 multi-layer core-shell structure. Compared with NaYF _ 4:10% Er ~ (3 +) @ NaYF _ 4:10% Ho ~ (3 +) @ NaYF _ 4:1% Tm ~ (3 +) @ NaYF _ 4:1% Tm ~ (3 +) @ NaYF _ 4 multi-layer core-shell structure, and the co-doped NaYF _ 4:10% Er ~ (3 +),10% Ho ~ (3 +),1% Tm ~ (3 +) @ NaYF _ 4 core-shell structure, the luminescence intensity is increased by 1.9 and 16.7 times respectively at 1523 nm laser excitation, and the luminous intensity is increased by 2.1 and 14.5 times respectively at the excitation of 1157 nm laser; Under the excitation of 1213 nm laser, the luminescence intensity was increased by 1.4 and 6.7 times, respectively. The up-conversion luminescence mechanism of Er ~ (3 +), Ho ~ (3 +) and Tm ~ (3 +) was studied. The excitation spectrum of the nano-crystal containing the multi-layer core-shell structure of the isolation layer is tested, and the response range of the infrared band below the silicon band gap is expanded to 270 nm. In this paper, the quantum cutting process of the (3 +)-Yb ~ (3 +)-doped pair, Pr ~ (3 +)-Yb ~ (3 +)-doped pair and Er ~ (3 +) single-doped fluoride nano-crystal on the ultraviolet light was studied with NaYF _ 4 as the matrix. Controlling the morphology and size of the nano-crystal of NaYF _ 4:2% Tb ~ (3 +), x% Yb ~ (3 +) (x = 0,20,40,60,80) by controlling the doping concentration of Tb ~ (3 +) to 2%, and obtaining the nano-particles with uniform size and uniform dispersion. It is found that with the increase of the doping concentration of Yb ~ (3 +), its quantum cut-off luminescence is enhanced; after more than 20%, the luminescence is gradually reduced. By studying the dependence of the luminescence intensity and the excitation power, the quantum cutting mechanism is proposed, and the quantum cutting efficiency is 183.7% by the theoretical calculation. The effect of the shell layer on the quantum cut of NaYF _ 4:2% Tb ~ (3 +), x% Yb ~ (3 +) (x = 0,20,40,60,80) was studied. Under the blanket of the inert shell, the emission of the quantum cut was enhanced, and the trend was changed compared with that of the core. The doping concentration of Yb ~ (3 +) is 80%, and the light emission is the strongest. The two processes of conversion (Er ~ (3 +)) and quantum cutting (Tb ~ (3 +)-Yb ~ (3 +)) are realized by multi-layer core-shell structure. The synthesis of NaYF _ 4:10% Er ~ (3 +) @ Na Lu F_4@NaYF_4:2% Tb ~ (3 +),20% Yb ~ (3 +) @ NaYF _ 4 core-shell structure nanocrystals, Na Lu F _ 4 as the intermediate isolation layer not only effectively weaken the cross relaxation in the two doped shell layers, but also the atomic mass difference of Lu and Y makes it possible to directly observe the structure of the multi-layer core-shell by the transmission electron microscope. The quantum efficiency of the upconversion and quantum cutting process was measured by relative method, and the quantum yield was about 3.6% by using NaYF _ 4:10% Er ~ (3 +) @ NaYF _ 4 as the standard sample. The quantum yield of the quantum cut was about 130%.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ422;TB383.1

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