氮掺杂石墨烯量子点的激发波长依赖性发光研究

Origin of excitation wavelength dependent photoluminescence of nitrogen-doped graphene quantum dots

激发波长依赖发光是碳基荧光材料中有趣的光学性质之一,其在不同激发波长下呈现的多彩发光对某些实际应用很重要.本文以氧化石墨烯为碳源,采用酸氧化法制备了尺寸约为3~5nm的少层石墨烯量子点(GQDs),然后将其与乙二胺(EDA)在160℃下进行水热反应,得到了石墨烯边缘氮掺杂的石墨烯量子点(NGQDs).采用傅立叶变换红外光谱(FTIR)证实了N-GQDs中酰胺键和胺C-N键的形成.GQDs的吸收主要来自C=C的π-π*跃迁(265nm)和C-O相关的n-π*跃迁(340nm),而N-GQDs中出现了C(=O)NHR相关的新能级(386nm).GQDs荧光峰随着激发光波长的移动Δλem/Δλex呈现线性变化,斜率约为0.43,而N-GQDs的Δλ_(em)/Δλ_(ex)出现两段线性变化,激发波长在420nm以后斜率增大到0.78,表明C(=O)NHR相关的荧光偶极子具有更强的激发波长依赖性发光特性.

The excitation wavelength dependent photoluminescence is a common phenomenon observed in the carbon-based fluorescent materials.It can afford multi-PL colors under the different excitation wavelengths,that is important for certain practical applications.In this work,a few layer graphene quantum dots（GQDs）with a size of 3-5nm were prepared via acidic oxidation of graphene oxide,and then were treated with ethylenediamine（EDA）under 160 ℃hydrothermal to obtain the nitrogen doped graphene quantum dots（N-GQDs）.Fourier transform infrared spectroscopy（FT-IR）demonstrated that the C-N bonds of amide and amine were formed.The PL excitation peaks of 265 nm and 340 nm can be attributed to the C=C relatedπ-π＊transitions and C-O related n-π＊transitions,respectively.New energy levels was observed at 386 nm due to C（=O）NHR related local molecular structure.The slope of the change in the peak emission wavelength for a given change in excitation wavelength,Δλ_（em）/Δλ_（ex） creating a linear slope ~0.43,but theΔλ_（em）/Δλ_（ex） shows two linear range,creating a larger slope^0.78when λ_（ex）420nm.So the C（=O）NHR related fluorescence dipole induces stronger excitation wavelength dependent photoluminescence.