Enhancement of optical and photo-physical properties of fluorescein dye by CdS quantum dots

Abstract A fluorescence enhancement strategy was successfully demonstrated by complexing fluorescein dye with cadmium sulfide (CdS) semiconductor quantum dots (QDs). The influence of varying QD concentrations on the photophysical behavior of 1 × 10⁻ 4 M fluorescein revealed that 5% w/w CdS QDs yielded the optimal balance for energy transfer efficiency and spectral modulation. Additionally, the effect of different dye concentrations within the complex was evaluated to understand concentration-dependent emission dynamics. Comprehensive photophysical characterization of the [Fluorescein: CdS QDs] system in ethanol was conducted, with particular focus on the underlying energy transfer mechanism. FRET-based analyses were employed to extract key parameters, including the critical transfer distance ( R ₀), thereby elucidating the nature and extent of QD-to-dye energy coupling. Fluorescence enhancement efficiencies were systematically studied under variable input powers using a continuous-wave blue diode laser ( λ = 450 nm). The QD-dye hybrid exhibited relatively high emission efficiency, along with a significantly elevated fluorescence quantum yield.