Photoluminescence of Drying Droplets with Silicon Nanoparticles

This study is dedicated to the formation of structures during drying of droplets of sols of silicon nanoparticles (SiNPs) in dimethylsulfoxide (DMSO) with a diameter of 1-5 mm on the horizontal glass and mica surfaces. Drying of such droplets with pinning (sticking) of the droplet contact line causes gradual gathering of the SiNPs on its edge with the formation of a thin ring. It has been found that the integral photoluminescence intensity I_PL greatly varies during the drying process. At the initial stage, I_PL monotonically decreases by several orders of magnitude and then abruptly increases several times at the final stage of ring formation. It has been shown that the rate of I_PL decrease is maximal at a very early stage and depends both on the aggregative state (solid film SiNPs/sols of the SiNPs) and volume of the SiNPs sols. It is minimal for the solid film SiNPs and gradually increases as the volume of SiNPs sol in DMSO decreases (optical cell → big droplet → small droplet). The obtained experimental dependencies between the luminescence decrease rate and aggregative state and volumes of the SiNPs sol in DMSO are attributed to the combination of three mechanisms of luminescence quenching: photobleaching, quenching with atmospheric oxygen, and Förster resonance energy transfer quenching. The appearing of the luminescence leap at the final stage of ring formation is associated with the emergence of cracks in the ring.