研究了甲基橙溶液的pH对纳米银荧光增强效应的影响。 当pH 1.5和2.1时, 纳米银对溶液的吸收光谱影响甚小。 当pH 3.1时, 吸收峰蓝移26 nm, 且强度明显降低。 当pH值在3.8～8.2范围时, 不仅吸收峰蓝移而且在426～456 nm出现宽吸收带。 在任何pH值的甲基橙溶液中加入纳米银, S2→S0跃迁荧光发射带强度下降, 但下降比率受pH值影响不大； S1→S0跃迁荧光发射带强度增强, 其增强比率受pH值影响较大。 当pH 2.1时, 荧光增强比率最大； 当pH 4.8时, 荧光增强比率最小。 分析认为, pH值对甲基橙溶液光谱性质的影响与不同pH值条件下甲基橙分子结构的改变以及分子在纳米银粒子表面不同的吸附方式、 介质环境等因素相关, 尤其与甲基橙分子与纳米银粒子间的距离密切相关。

In the present paper, the effect of pH value of methyl orange solution on the fluorescence enhancement effect of silver nanoparticles was studied. When pH 1.5 and 2.1 the absorption spectra had little change with added silver colloid. When pH 3.1 a blue shift of 26 nm and a decrease in the intensity of the absorption peak were observed. When the values of pH are in the range of 3.8～8.2 a blue shift of the absorption peak and a 426～456 nm broad absorption band were observed. When silver colloids were added into methyl orange solutions with different pH values the fluorescence intensity of S2→S0 electronic transition decreased and was little impacted by pH value; while the fluorescence intensity of S1→S0 electronic transition was enhanced and was impacted by pH value. The largest and smallest fluorescence enhancement ratios were observed at pH 2.1 and 4.8, respectively. The results indicated that the reasons of effect of pH of methyl orange solution on the fluorescence enhancement of silver colloid depend on methyl orange structure, molecular adsorption mode, media and so on, especially the distance between molecule and silver nanoparticle.