有趣的贵金属表面等离激元的光学性质, 尤其是在发光增强领域的表现, 使得它已经成为全球的一个研究热点。 表面等离激元就是光与贵金属中的自由电子相互作用时, 自由电子和光波电磁场由于共振频率相同而形成的一种集体振荡态。 该文研究了碲化物玻璃中银纳米颗粒的表面等离激元共振增强铒离子的发光。 我们测量了吸收谱、 激发谱、 发光谱以及荧光寿命。 首先, 我们挑选365.5和379.0 nm吸收峰作为激发波长测量了385～780 nm波长范围的可见发光光谱, 发现有4个发光峰, 依次位于408.0, 525.0, 546.0和658.5 nm, 容易指认出它们依次为铒离子的2H9/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2和4F9/2→4I15/2的荧光跃迁; 可以计算出［80 nm平均粒径纳米银的Er3+(0.5%)Ag(0.2%): 碲化物玻璃的样品A］的上述4个可见发光的峰值强度是［Er3+(0.5%): 碲化物玻璃的样品C］的大约1.44～2.52倍。 同时, ［50 nm平均粒径纳米银的Er3+(0.5%)Ag(0.2%): 碲化物玻璃的样品B］的上述4个可见发光的峰值强度是样品C的大约1.08～1.55倍。 随后, 我们挑选365.5和379.0 nm 吸收峰作为激发波长测量了928～1 680 nm波长范围的近红外发光光谱, 发现近红外波段有两个发光峰, 位于979.0和1 530.0 nm, 容易指认出它们依次为铒离子的4I11/2→4I15/2和4I13/2→4I15/2的荧光跃迁; 同样可以计算出样品A的上述2个近红外发光的峰值强度是样品C的大约1.43～2.14倍。 同时, 样品B的上述2个近红外发光的峰值强度是样品C的大约1.28～1.82倍。 因此, 发光的最大增强大约是2.52倍。 从荧光寿命动力学实验, 我们发现样品A的荧光寿命为τA(550)=43.5 μs, 样品B的荧光寿命为τB(550)=43.2 μs, 样品C的荧光寿命为τC(550)=48.6 μs。 这些实验结果证实了τA≈τB ＜τC。 它意味着样品(B)相对于样品(C)的发光增强是源于自发辐射增强效应。 然而, 它也意味着样品(A)相对于样品(B)的发光增强是源于纳米银颗粒的粒径尺寸r效应。 也就是说当粒径尺寸r增大的时候, 散射截面Cs和r6成正比, 而吸收截面Ca和r3成正比, 因此散射截面Cs增大的速度会远大于吸收截面Ca增大的速度, 而散射截面Cs是荧光增强的原因, 吸收截面Ca是荧光减弱的原因, 所以随着银纳米颗粒尺寸的增大, 其散射截面占主要部分, 当发光材料和金属表面等离子体SP发生耦合时, 能量快速的转移到金属表面等离子体SP上, 而后被散射到远场, 这有利于增强荧光。 其综合的结果就导致了发光强度会随r的增大而增强。 上述实验的结果对太阳能电池的光伏发电和生物物理应用等领域都有着很好的应用前景。

Interesting optical properties of metal surface plasmon, especially the behavior on luminescence enhancement field, have become a hot research topic globally. The surface plasmon is just a kind of collective oscillation made of free electron and light electromagnetic fields because their resonant frequencies are similar when they are interacting with each other. In present paper, the erbium luminescence resonant enhanced by surface plasmon of Ag nanoparticles (NPs) in telluride glass is studied. The absorption, excitation, luminescence spectra, and lifetime are measured. First, we select the 365.5 and 379.0 nm excitation peaks as excitation wavelength to measure the visible luminescence spectra in the wave range of 385～780 nm. We find 4 luminescence peaks positioned at 408.0, 525.0, 546.0, and 658.5 nm. They are, respectively, the fluorescence transitions of 2H9/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 of Er3+ ions. It is easy to calculate the peak intensities of the above 4 visible luminescence of (A) Er3+(0.5%)Ag(0.2%): Telluride glass with the average diameter of 80 nm for Ag NPs are about 1.44～2.52 times larger than that of the (C) Er3+(0.5%): Telluride glass. Moreover, the peak intensities of the above 4 visible luminescence spectra of (B) Er3+(0.5%)Ag(0.2%): Telluride glass with the average diameter of 50 nm for Ag NPs are about 1.08～1.55 times larger than that of the sample (C). Then, we select the 365.5 and 379.0 nm excitation peaks as excitation wavelength to measure the near infrared luminescence spectra in the wave range of 928～1 680 nm. It is found that near infrared luminescence peaks are positioned at 979.0 and 1 530.0 nm. They are, respectively, the fluorescence transitions of 4I11/2→4I15/2 and 4I13/2→4I15/2 of Er3+ ions. The peak intensities of the above 2 near infrared luminescence spectra of sample (A) are about 1.43～2.14 times larger than that of the sample (C). Similarly, the peak intensities of the above 2 near infrared luminescence spectra of sample (B) are about 1.28～1.82 times larger than that of the sample (C). Therefore, the largest enhancement is about 2.52 times larger. From the experiments of fluorescence lifetime dynamics, we find that the 550 nm fluorescence lifetime of sample (A) is about τA(550)=43.5 μs, that of sample (B) is about τB(550)=43.2 μs, and that of sample (C) is about τC(550)=48.6 μs. The experimental results illustrate that τA≈τB＜τC. This means that the luminescence enhancement of sample (B) relative to sample (C) results from the spontaneous radiation enhancement effect. However, this also means that the luminescence enhancement of sample (A) relative to sample (B) results from the Size r effect, in which the increased of the scattering cross section Cs is much larger than that of the absorption cross section Ca when r is enlarged, because the scattering cross-section Cs are proportional positive ratio to r6 and the absorption cross-section Ca are proportional positive ratio to r3. As we know that the scattering cross-section Cs is the reason for the increase of fluorescence, meanwhile the absorption cross-section Ca is the reason for the decease of fluorescence. When r is increase, scattering cross-section Cs is the main part. When luminescent material couples with the metallic surface Plasmon, the energy is transferred quickly to metallic surface Plasmon, and then scattered to the far field. It’s beneficial for the enhancement of fluorescence. As a comprehensive result, the fluorescence is enhanced when r is enlarged. It has excellent application prospects in the optogalvanic electricity generation of solar cell and biophysical application other as well as fields.