荧光俘获效应对Er^(3+)/Yb^(3+)共掺杂碲钨酸盐玻璃光谱性质的影响

Effect of Radiation Trapping on Spectroscopic Properties of Er^(3+)/Yb^(3+) Codoped Tungsten-Tellurite Glasses

制备了掺杂浓度相同而厚度不同的Er3+/Yb3+共掺杂碲钨酸盐玻璃样品,测量了样品的吸收光谱和970nmLD激发下的Er3+离子1.5μm发射的荧光光谱和荧光寿命,计算了Er3+离子的发射截面,研究了荧光俘获效应对Er3+离子1.5μm发射的光谱性能的影响。结果表明,样品中Er3+离子存在很强的荧光俘获效应,且荧光俘获效应随样品厚度的增加而增强。荧光俘获效应使测得的荧光寿命比计算的自发辐射寿命要长,随样品厚度的增加,Er3+离子1.5μm发射的荧光寿命增加;其荧光有效线宽Δλeff与次峰值强度和主峰值强度的比值Is/Ip也增加,且Δλeff与Is/Ip存在很好的线性关系。首次提出采用Er3+1.5μm波段荧光谱的次峰值强度和主峰值强度的比值Is/Ip与从McCumber理论计算得到的次峰值发射截面和主峰值发射截面的比值(σes/σep)的差值或比值来判断基质中Er3+1.5μm波段荧光俘获效应强弱的方法。

The Er^(3+)/Yb^(3+) codoped TeO_2-WO_3-ZnO (TWZ) glass samples with same doping concentration and different thickness were prepared. The absorption spectra, 1.5 μm emission spectra and fluorescence lifetimes of Er^(3+), excited by 970 nm, were measured. The absorption cross-section was calculated based on measured absorption spectra at room temperature. The emission cross-sections were calculated by McCumber theory. The effect of radiation trapping on the spectroscopic properties of Er^(3+) in TWZ glass was discussed. Because of the high refractive index of the glass and very large overlapping around 1.5 μm between the absorption cross section and the emission cross section of Er^(3+) in TWZ glass, the radiation trapping in the TWZ glass samples was very strong. The radiation trapping became stronger with the increase of the thickness of samples. Due to the effect of the radiation trapping, the measured fluorescence lifetime was longer than the calculated one, which caused the quantum efficiency large than 100%. The emission spectra were also broadened and the emission peak wavelength shifted to the longer wavelength slightly. When the sample thickness increased from 0.50 mm to 3.15 mm, the fluorescence lifetime increased from 2.60 ms to 3.10 ms and the quantum efficiency increased from 111% to 132%. At the same time, the fluorescence effective line width, Δλ_(eff), increased from 76.2 nm to 91.7 nm and the emission intensity ratio of the main peak to the second peak, I_s/I_p, also increased gradually. The fitting results showed that the Δλ_(eff) increased linearly with the increasing of the ratio value of I_s/I_p. Based on the obtained linear equation for Δλ_(eff) and I_s/I_p, the effective line width in the glass sample without the exis-tence of radiation trapping was deduced, which was 72.1 nm. The value was very close to the Δλ_(eff) calculated from the emission cross-section curve, which was 70.3 nm. So we suggested that the Δλ_(eff) calculated from the emission cross-section curve could be used to determine the Δλ_(eff) of Er^(3+) emission at 1.5 μm without the radiation trapping effect. For the first time, the opinion that the ratio of the I_s/I_p to the σ_(es)/σ_(ep), or the difference between the I_s/I_p and the σ_(es)/σ_(ep) can be used to evaluate the radiation trapping of Er^(3+) at 1.5 μm band. Here the σ_(es) and the σ_(ep) are the emission cross sections at wavelength of the second peak and the strongest peak, respectively, calculated by McCumber theory.