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The nonlinear optical properties of carbon dots have been in the spotlight in recent years. In light of the complexity and diversity of factors affecting the nonlinear optical properties of carbon dots, how to reveal the origin and physical mechanism of the nonlinear optical properties of carbon dots accurately has become a problem. In this work, a template-free method was designed to prepare carbon dots via solid-phase reaction with phloroglucinol as a single carbon source and sodium bisulfate as the catalyst. This method is simple, green, safe, and easy to be prepared on a large scale. Three carbon dots with different luminous colors were obtained by simply adjusting the reaction temperature. The rise of reaction temperature affects the surface functional groups, and then hinders the luminescence of surface states, leading to the change of luminescence properties. The nonlinear optical properties of carbon dots were analyzed by the Z-scan technique. Surprisingly, all carbon dots have nonlinear optical responses, but there are differences in performance. Results prove the increase in sp2 domains may contribute to the significant improvement of the nonlinear optical properties of carbon dots, indicating a direction to improve the nonlinear optical properties of carbon dots. [ABSTRACT FROM AUTHOR]

Using polyaluminum chloride residue as raw material, the effects of roasting temperature, roasting time, additive ratio and other factors on the activation effect of silicon dioxide in polyaluminum chloride residue were studied by single factor experiment and orthogonal design, and the technological conditions for producing silicon fertilizer from polyaluminum chloride residue were determined. The results show that the significant influence of three factors effective silicon content and the activation rate of silicon in polyaluminum chloride waste residue is as follows: activator dosage > calcination temperature > calcination time. The amount of activator and calcination temperature have obvious influence on the content of effective silicon in the calcined product, while the calcination time has no obvious influence on the content of effective silicon in the calcined product. With the increase of the amount of activator, the effective silicon content in the product increases. When the amount of activator reaches 41%, the effective silicon content tends to be stable, and the correlation coefficient between the amount of activator and the effective silicon content reaches 0.9829; with the increase of calcination temperature, the effective silicon content in the product increases, and reaches the peak after 1250°,when the temperature is 1240~1270°, the time is 30~40 min and the dosage of activator is 41%~45%, the content of effective silicon in the product is the highest, reaching about 30%. [ABSTRACT FROM AUTHOR]