| Carbon quantum dots(CDs) are spherical dispersed nano particles, their main ingredient is carbon, particles’ size is less than 10 nm, they are widely used due to the good fluorescence. Compared with the semiconductor quantum dots, CDs have the advantage of low toxicity, biocompatibility, cheap and easy to obtain. Currently, the research on CDs mainly concentrated in the biological detection, sensor, nonlinear optics, photoelectric conversion and photocatalysis aspects. Research the nonlinear optical properties of CDs, which having important sense to explore the properties of CDs and obtain the excellent nonlinear materials.In this paper, we used Z-scan technique to measure the nonlinear absorption properties of water-soluble and oil-soluble carbon quantum dots of the fluorescence emission wavelengths were 450 nm and 550nm(when excitation wavelength is 400nm). Using based on phase object’s pump-probe technology to study the ultrafast dynamics of two kinds of CDs, the study found:1. In the nanosecond laser pulses, the water-soluble carbon quantum dots having nonlinear absorption characteristics, and the CDs of fluorescence emission wavelength is 450 nm presents saturable absorption, the CDs of fluorescence emission wavelength is 550 nm presents reverse saturable absorption. Oil-soluble carbon quantum dots no nonlinear absorption characteristics. We educed CDs particles’ size affects its nonlinear absorption, and this relates to quantum size effect.2. In the picosecond laser pulse, different emission wavelengths’ CDs of water-soluble and oil-soluble still exhibit different non-linear absorption characteristics, the water-soluble CDs of fluorescence emission wavelength is 450 nm and the oil-soluble CDs of fluorescence emission wavelength is 550 nm showed saturable absorption, and water-soluble CDs of fluorescence emission wavelength is550 nm and oil-soluble CDs of fluorescence emission wavelength is 450 nm showed reverse saturable absorption. We get that nonlinear absorption of CDs is not only affected by the quantum size effect, but also affected by the solvent effect.3. In the femtosecond laser pulse, firstly, we compared the different excitation energy affected CDs’ nonlinear absorption properties, and found that as the excitation energy increases, nonlinear absorption coefficient decreases, mainly due to two-photon absorption effect. Secondly, compared the effects of different solvents to the nonlinear absorption of CDs, the water-soluble CDs of fluorescence emission wavelength is 450 nm presents reverse saturable absorption, the oil-soluble CDs of fluorescence emission wavelength is 450 nm also presents reverse saturable absorption, but the nonlinear absorption properties of oil-soluble CDs is stronger than water-soluble CDs, we can derive that solvent affect nonlinear absorption coefficient of CDs. Finally, comparing the effects of different fluorescence emission wavelength of CDs, and once again proven nonlinear absorption of CDs are affected by quantum size effect.4. Using based on phase object’s pump-probe technology to study the femtosecond ultrafast dynamics of CDs. When the laser input wavelength is 515 nm, the laser pulse width is 190 fs, we obtain the kinetic curve of water-soluble CDs and oil-soluble CDs. |
