Excitation-Intensity-Dependent Color-Tunable Dual Emissions from Manganese-Doped CdS/ZnS Core/Shell Nanocrystals

摘要

Manganese-doped semiconductor nanocrystals exhibit unique optical and magneto-optical properties, which make them excellent testbeds for both fundamental studies and technological applications in fields ranging from spintronics to biomedical diagnosis. Large Zeeman effects have been observed in Mn-doped ZnS, ZnSe, and CdSe nanocrystals, which indicate that quantum-confined excitons feel a large effective magnetic field of up to 400 Tesla induced by the presence of a few Mn~(2+) ions inside the nanocrystals. Spin-polarizable excitonic photoluminescence (PL) has also been observed in Mn-doped CdSe nanocrystals. Additionally, Mn dopants can introduce new luminescence properties to nanocrystals, resulting in particles with dual emission properties. Recent work has shown that Mn-doped CdS/ZnS core/shell nanocrystals possess dopant-position-dependent PL properties, and Mn dopants can be used as a radial pressure gauge for measuring the lattice strains in the nanocrystals. Moreover, the PL from Mn dopants in Mn-doped ZnSe nanocrystals can be reversibly depleted by light-driven modulation using two excitation sources with different wavelengths. Therefore, Mn-doped nanocrystals are a potential new class of optical microscopy markers that can improve optical imaging resolution in the far field. Herein, we show that Mn-doped CdS/ZnS core/shell nanocrystals exhibit color-tunable dual emissions under a single-wavelength excitation source at varying intensities. This new finding provides important insight into the fundamental mechanisms of internal electronic transitions in Mn-doped semiconductor nanocrystals, which is important for applications such as photoswitchable markers for biomedical imaging and diagnosis.