Carbon quantum dots capped with metal ions for efficient optoelectronic applications

Abstract

Fluorescent carbon dots (C-dots) with high optical properties and biocompatibility have great potential for various types of optoelectronic applications. Although many approaches have been used for producing high-quality C-dots, it is still a challenge to produce high-quality C-dots with required properties via a simple and efficient approach. In this work, by controlling the addition of different types of divalent (e.g. Mn and Sr) or trivalent (e.g. Al, Ga and In) metal ions, we synthesized fluorescent C-dots with single or double emissions with quantum yield (QY) as high as 61% using a simple heating approach. Transient fluorescence spectroscopy and transient absorption spectroscopy reveal that the double emission and an excitation-dependent photoluminescence behavior of trivalent ion-capped C-dots originate from the existence of multiple energy levels. Based on these optical properties, the as-prepared C-dots can be effectively used as building blocks for fabricating various types of optoelectronic devices. A single emission Mn-C-dot based large-area luminescent solar concentrator (LSC) (225 cm²) achieved a power conversion efficiency (PCE) of 1.3% under natural sunlight (50 mA cm⁻²); double emission Al–C-dots showed excitation wavelength dependent fluorescent codes, showing great potential for application in developing anti-counterfeiting codes; and magnetic tests showed that Mn-capped C-dots are superparamagnetic and this may be useful for magnetically driven fluorescence imaging in biomedical applications. This study offers an eco-friendly and efficient approach for producing large-scale high-quality C-dots, demonstrating great potential for optical and electrical applications.