Structural and optical properties of Mn2+-doped ZnCdS/ZnS core/shell quantum dots: New insights in Mn2+ localization for higher luminescence sensing

The synthesis methods (one- or two-pot) of stable Mn2+ doped ZnxCd1-xS and ZnxCd1-xS/ZnS quantum dots are reported in this study with a quantum yield (QY) of ∼ 60% in anhydrous and ∼ 30% in aqueous media for Mn2+ photoluminescence (PL). Mn2+-localization in the prepared QDs was characterized by electron paramagnetic resonance (EPR). Structural parameters were established by X-ray diffraction (XRD). Femtosecond transient absorption spectroscopy, time-gated luminescence measurements allowed to elucidate the relaxation dynamics of exciton, traps and 4T1 excited Mn2+. High-order derivative spectral analyses of the photoluminescence (PL) bands of Mn2+ accompanied with Gauss peaks decomposition have been employed. This analysis revealed narrow peaks in the spectral range from green (∼537 nm) to far-red (∼655 nm). These PL peaks can be associated with different locations of Mn2+ in QDs that are characterized by different strengths of the crystal field around Mn2+. Dopant localization sites and relaxation processes control the quantum yield of Mn2+, providing higher photocatalytic activity, pronounced electroluminescence, and higher sensitivity.