Preparation And Optical Properties Of Diamond-structured Carbon Nanocrystals

As one of the members of the fluorescent nanomaterials,the carbon nanoparticles have special p Hysical and chemical properties and superior fluorescence properties,so they have attracted more and more research interest.Previously,the researchers had paid much attention to the developments of the various facial and economical synthesis methods for the carbon nanoparticles as well as explorations of their luminescence mechanisms.The luminescence of the carbon nanoparticles is tunable,and their surface engineering can make their fluorescence controllable.We mainly studied the synthesis of the carbon nanoparticles by using the hydrothermal method,discussed the variations of their crystal structures,and studied their luminescence properties,focusing on how the crystallization temperature influences their luminescence properties.The diamond-structured carbon nanoparticles with sizes of 2.5–9.5 nm were synthesized by using the hydrothermal method employing glucose as the source material.We studied how the crystallization temperature influences the luminescence properties of the diamond-structured carbon nanoparticles.The result shows that the sizes of the synthesized carbon nanoparticles depend only weakly on the crystallization temperature.In contrast,the crystallization temperature strongly affects their luminescence properties.The peak intensity and wavelength of the different emission bands of the diamond nanoparticles have different dependence on the crystallization temperature.The result shows that surface functional groups of the diamond nanoparticles are dependent on the crystallization temperature,and the lower temperature is favorable for the formation of the C=O related groups,when the crystallization temperature rises,partial C=O groups will be converted into C–O–C groups.As a result,the carbon nanoparticles synthesized at higher temperatures have more C–O–C groups on their surfaces.Such variations lead to the variations of the associated surface defects,and then results in the crystallization temperature dependence of the luminescence properties of the diamond nanoparticles.We used the alkali solution to tune the p H of the diamond nanoparticles synthesized hydrothermally,and studied how the p H affects the luminescence properties and the luminescence lifetimes.Through analysis of the fluorescence spectra,we found that the luminescence properties of the diamond nanoparticles are dependent on the p H value.This is because the OH~–ions in the solution change the surface functional groups of the carbon nanoparticles,and thus change the surface fluorescence defects,thereby leading to the variation of the fluorescence.The luminescence mechanism of the carbon nanoparticles is always under debate.Previously,some researchers regarded that the luminescence of the carbon nanoparticles stems from their surface defects,and thought that the large amount of oxygen-containing surface functional groups of the carbon nanoparticles determine their luminescence properties.We observed the influence of the variation of the surface defects of the carbon nanoparticles on their luminescence properties,either by changing the crystallization temperature or by changing the p H value.The research results tend to support that the luminescence of the carbon nanoparticles originates from the surface defects.