Efficient Photoluminescence of Mn2+-Doped ZnS Quantum Dots Sensitized by Hypocrellin A

Xianlan Chen,Shanqing Pan,Ling Shi,Wei Liu,Guowei Zhang,Na Wu

doi:10.1155/2015/412476

Xianlan Chen, Shanqing Pan + Show 4 more

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https://doi.org/10.1155/2015/412476

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Abstract

Mn2+-doped ZnS semiconductor quantum dots reveal remarkably intense photoluminescence with the4T1(4G) f6A1(6S) transition. In this study, following growth doping technique, Mn2+-doped ZnS quantum dots (ZnS:Mn2+QDs) with high-quality optical properties and narrow size distribution were synthesized successfully. The dopant emission has been optimized with various reaction parameters, and it has been found that the percentage of introduced dopant, reaction temperature, and time as well as the pH of a reaction mixture are key factors for controlling the intensity. Photoluminescence emission (PL) measurements of ZnS:Mn2+QDs show Mn2+d-d orange luminescence along with band-edge blue luminescence. Moreover, the electron transfer from singlet states of hypocrellin A (HA) to colloidal ZnS:Mn2+QDs has been examined by absorption spectra and fluorescence quenching. The absorption spectrum gave an evidence of the increases in the extinction coefficient and the red-shift of the absorption maxima in the absorption spectra of HA in the presence of ZnS:Mn2+QDs, demonstrating the occurrence of surface interactions between the sensitizer and the particle surface. Fluorescence quenching by ZnS:Mn2+QDs also suggested that there were a complex association between HA and ZnS:Mn2+QDs, which was necessary for observing the heterogeneous electron-transfer process at the interface of sensitizer-semiconductor.

Highlights

Light emitting semiconductor nanocrystals, otherwise known as quantum dots (QDs), have been widely investigated during the last two decades in view of their size-tunable optical properties, wide range of excitations, emission color purity, high quantum efficiency, and applications as a light emitting source in various optoelectrical devices, imaging, solar cells, environment, remediation, and therapeutics and in biological applications [1, 2]
We report here large-scale synthesis of high-quality Mn2+-doped ZnS nanocrystals using common and inexpensive chemicals following a simple and reproducible synthetic technique; hypocrellin A (HA) acting as an electron donor adsorbs directly onto the surface of Mn2+-doped ZnS nanocrystals and can transfer an electron from its singlet excited state into the conduction band of Mn2+-doped ZnS nanocrystals
The fluorescence emission of HA was quenched upon successive addition of ZnS:Mn2+ QDs to a solution of 1.8315 × 10−4 M HA (Figure 10). This quenching behavior was similar to that of other organic dyes used for the sensitization of large-band gap semiconductors [25], which were caused by the electron injection from the singlet excited state of sensitizers to the conduction band of colloidal ZnS:Mn2+ QDs. This suggested that there was a complex association between HA and

Summary

Introduction

Otherwise known as quantum dots (QDs), have been widely investigated during the last two decades in view of their size-tunable optical properties, wide range of excitations, emission color purity, high quantum efficiency, and applications as a light emitting source in various optoelectrical devices, imaging, solar cells, environment, remediation, and therapeutics and in biological applications [1, 2]. It is widely believed that the excitation takes place through the host lattice and is followed by energy transfer to the impurity to yield the Mn luminescence band in Mn2+doped ZnS quantum dots. The chemistry, photochemistry, and photophysics of HA have been studied and reviewed [20], but photosensitization of the doping semiconductor nanocrystals with HA by the injection of electrons from its singlet excited state in aqueous solution is little studied. We report here large-scale synthesis of high-quality Mn2+-doped ZnS nanocrystals using common and inexpensive chemicals following a simple and reproducible synthetic technique; HA acting as an electron donor adsorbs directly onto the surface of Mn2+-doped ZnS nanocrystals and can transfer an electron from its singlet excited state into the conduction band of Mn2+-doped ZnS nanocrystals

Reagents and Apparatus

Results and Discussion

Conclusions