Preparation And Research On Surface Modification Of Colloidal Silicon Quantum Dots

Colloidal silicon quantum dots(Si NCs)are quasi-zero-dimensional semiconductor nanomaterials that are used in a wide range of applications because of their unique optoelectronic properties,non-toxicity,low cost of preparation,good dispersion,and good biocompatibility.The Si NCs can obtain photoluminescence(PL)in the visible range and the optical properties are adjustable.However,the luminescence mechanism is not systematically explained and the fluorescence quantum yields(PL QYs)is generally low.After several years of research,people have made in-depth research on the preparation and surface modification of Si NCs,and have a deep understanding of its physical and chemical properties and modification methods.In this paper,femtosecond(fs)pulsed laser in liquid was used to ablate the target to prepare the functionalized nanoparticles.The relationships between the laser parameters,solution environment of the fslaser and size as well as fluorescence of the nanoparticles were studied.The main contents are as follows:(1)Si NCs were prepared by ablation of single crystal silicon powder in1-octene solution via fslaser ablation in liquid(LAL)method.The structure and optical properties of Si NCs were studied under different laser ablation time(LAT).The results show that the average size of Si NCs decreases from ?4.23 to 1.42 nm as LAT is extended from 30minutes to 120 minutes,and with LAT increasing,surface passivations of Si NCs with carbon chains were enhanced.Moreover,oxidation remains almost unchanged.The room-temperature blue emissions peaked at 405 and 430 nm originated from the radiative recombination of electron-hole pairs via the oxygen-deficient centers related to Si-C-H₂and Si-O-Sibonds of Si NCs prepared in 1-octene,respectively.Due to good surface passivation and increased density of Si NCs,the PL QYs of Si NCs increased significantly with the increasing ablation time.(2)Si NCs were prepared by ablation of single crystal silicon powder in styrene solution via fs LAL method,and 0 to 11.1 vol.%of HF was added to the mixed solution.The structural transformation,PL properties and significantly improved PL QYs of the prepared Si NCs were investigated in detail.The results show that the average particle size of Si NCs decreases from 6.5 to 2.7 nm,the surface alkyl group-related molecular passivations were enhanced and the dangling bond densities between Si/SiO₂ interface regions were reduced with increasing of HF concentration.It is shown that adding HF to the styrene solution is found to remove the oxide layers and then replace the related dangling bonds by alkyl-related bonds under fslaser ablation,leading to the lower defect densities of non-radiative P_b defect centers.We propose that the blue emission of Si NCs originates from the following process:when illuminated,excitons are excited at the?point in Si NCs,then some excitons are captured by the non-radiative P_bcenter,while the rest of excitons transfer to the alkyl-related radiation recombination center and emit blue PL at2.82 and 3.01 eV.As the HF concentration increased from 0 to 11.1 vol.%,effective passivation and inhibition of non-radiative P_bcenters resulted in an increment of PL QYs from 16.3 to 76.5%.