The light of carbon dots: From mechanism to applications

As a class of carbon-based nanomaterials, carbon dots (CDs) have attracted enormous attention because of their tunable optical and physicochemical properties, such as absorptivity and photoluminescence from ultraviolet to near-infrared, high photostability, biocompatibility, and aqueous dispersity. These characteristics make CDs a promising alternative photonic nanoagent to conventional fluorophores in disease diagnosis, treatment, and healthcare managements. This review describes the fundamental photophysical properties of CDs and highlights their recent applications to bioimaging, photomedicine (e.g., photodynamic/photothermal therapies), biosensors, and healthcare devices. We discuss current challenges and future prospects of photonic CDs to give an insight into developing vibrant fields of CD-based biomedicine and healthcare.

Photonic Carbon Dots as an Emerging Nanoagent for Biomedical and Healthcare Applications.

Carbon-based quantum dots (CQDs), including spherical carbon dots and graphene quantum dots, are an emerging class of photoluminescent (PL) materials with unique properties. Great progress has been made in the design and fabrication of high-performance CQDs, however, the challenge of developing solid-state PL CQDs have aroused great interest among researchers. A clear PL mechanism is the basis for the development of high-performance solid-state CQDs for light emission and is also a prerequisite for the realization of multiple practical applications. However, the extremely complex structure of a CQD greatly limits the understanding of the solid-state PL mechanism of CQDs. So far, a variety of models have been proposed to explain the PL of solid-state CQDs, but they have not been unified. This review summarizes the current understanding of the solid-state PL of solid-state CQDs from the perspective of energy band theory and electronic transitions. In addition, the common strategies for realizing solid-state PL in CQDs are also summarized. Furthermore, the applications of CQDs in the fields of light-emitting devices, anti-counterfeiting, fingerprint detection, etc., are proposed. Finally, a brief outlook is given, highlighting current problems, and directions for development of solid-state PL of CQDs.

Carbon-Based Quantum Dots with Solid-State Photoluminescent: Mechanism, Implementation, and Application.

Multicolor bandgap fluorescent carbon quantum dots (MCBF-CQDs) from blue to red with quantum yield up to 75% are synthesized using a solvothermal method. For the first time, monochrome electroluminescent light-emitting diodes (LEDs) with MCBF-CQDs directly as an active emission layer are fabricated. The maximum luminance of blue LEDs reaches 136 cd m-2 , which is the best performance for CQD-based monochrome electroluminescent LEDs.

Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light-Emitting Diodes

Single-component multicolor luminescence, particularly phosphorescence materials are highly attractive both in numerous applications and in-depth understanding the light-emission processes, but formidable challenges still exist for preparing such materials Herein, a very facile approach is reported to synthesize carbon dots (CDs) (named MP-CDs) that exhibit multicolor fluorescence (FL), and more remarkably, multicolor long-lived room temperature phosphorescence (RTP) under ambient conditions The FL and RTP colors of the CDs powder are observed to change from blue to green and cyan to yellow, respectively, with the excitation wavelength shifting from 254 to 420 nm Further studies demonstrate that the multicolor emissions can be attributed to the existence of multiple emitting centers in the CDs and the relatively higher reaction temperature plays a critical role for achieving RTP Given the unique optical properties, a preliminary application of MP-CDs in advanced anti-counterfeiting is presented This study not only proposes a strategy to prepare photo-stimulated multicolor RTP materials, but also reveals great potentials of CDs in exploiting novel optical materials with unique properties

Photo-Stimulated Polychromatic Room Temperature Phosphorescence of Carbon Dots

Due to the prominent characteristics of carbon-based luminescent nanostructures (known colloquially as carbon dots), such as inexpensive precursors, excellent hydrophilicity, low toxicity, and intrinsic fluorescence, these nanomaterials are regarded as potential candidates to replace traditional quantum dots in some applications. As such, research in the field of carbon dots has been increasing in recent years. In this mini-review, we summarize recent progress in studies of multicolor carbon dots focusing on potential photoluminescence (PL) mechanisms, strategies for effective syntheses, and applications in ion/molecule and temperature sensing, light emitting diodes and high-resolution bioimaging techniques.

Xiao Xiao Yao

Papers

Synthesis, applications and potential photoluminescence mechanism of spectrally tunable carbon dots