Investigation of Steady-State and Time-dependent Luminescence Properties of Colloidal InGaP Quantum Dots.
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Investigation of Steady-State and Time-dependent Luminescence Properties of Colloidal InGaP Quantum Dots. Subhasish Chatterjee1,3, Nikesh V. Valappil1 and Vinod M. Menon1,2 * 1
Laboratory for Nano and Micro Photonics (LaNMP)-Department of Physics, Queens CollegeCUNY, Flushing, NY, 2The Graduate Center of CUNY, New York, NY. 3 Department of Chemistry, City College of New York and the Graduate Center of CUNY, New York, NY. ABSTRACT Quantum dots play a promising role in the development of novel optical and biosensing devices. In this study, we investigated steady state and time-dependent luminescence properties of InGaP/ZnS core/shell colloidal quantum dots in a solution phase at room temperature. The steady state experiments exhibited an emission maximum at 650 nm with full width at half maximum of ~ 85 nm, and strong first-excitonic absorption peak at 600 nm. The time-resolved luminescence measurements depicted a bi-exponential decay profile with lifetimes of τ1~ 47 ns and τ2~ 142 ns at the emission maximum. Additionally, luminescence quenching and lifetime reduction due to resonance energy transfer between the quantum dot and an absorber are demonstrated. Our results support the plausibility of using these InGaP quantum dots as an effective alternative to highly toxic conventional Cd or Pb based colloidal quantum dots for biological applications. INTRODUCTION Quantum dot (QD), often described as an ‘artificial atom’, exhibits discrete energy levels and the spacing of the energy levels can be precisely modulated through the variation of their size [1]. Consequently, QDs act as robust light emitters with finely tunable fluorescence emission that asserts a great advantage over conventional organic chromophores [2]. Nanoscopic size, stability in organic and aqueous phases, strong fluorescence, and a combination of large molar absorbities and high quantum yields, are the unique properties that make QDs very attractive for biosensing and as fluorescent labels in biological research [2-5]. QDs show promising technological potential in the development of photonic transistors [6], photovoltaic devices [7], light emitting diodes [8], and lasers [1]. Furthermore, QDs can serve as efficient fluorescent donors in resonance energy transfer (RET) process [2, 9], a powerful tool for structural investigation of biological and synthetic macromolecules [10]. RET phenomenon involving a pair of fluorescent donor and quencher has been extensively utilized to depict biomolecular conformational changes, which are imperative to understand the structure-function characteristics of proteins [11] and nucleic acids [12, 13]. The long radiative lifetime of QDs (>10 ns) facilitates continuous and long-term tracking of slow biological process and conformational dynamics of biomolecules with large distance changes, a challenging task with conventional organic fluorophores [2-4]. Indeed, the applications of CdSe and CdS QDs have proven to be promising in this context [3, 4, 9, 12].
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