Mechanistic Insights and Controlled Synthesis of Radioluminescent ZnSe Quantum Dots Using a Microfluidic Reactor

We describe the controlled colloidal synthesis and characterization of ZnSe quantum dots using a continuous-flow microfluidic reactor. A systematic investigation of the synthetic route reveals a possible two-stage pathway for ZnSe nanocrystal formation. The first stage corresponds to the formation of zinc selenide nuclei at low temperatures (160 °C), followed by the growth of ZnSe nanocrystals at higher temperatures (340 °C). The quantum dots exhibit sharp exciton absorption, with tunable emission spectra between 370 and 430 nm. The photoluminescence of ZnSe nanocrystals is characterized by narrow emission linewidths of 14-21 nm. For the first time, we report luminescent emission from ZnSe nanocrystals upon X-ray excitation, revealing that radioluminescence emission is associated to confined excitons, and that the radioluminescence intensity is a linear function of the fluence/dose rate of X-rays. The precise control of the synthesis of particles with uniform sizes and excellent optical properties associated with the microfluidic synthesis opens a new avenue for the controlled production of heavy-metal-free luminescent and radioluminescent nanocrystals in flow.