Efficient Red/Near-Infrared-Emissive Carbon Nanodots with Multiphoton Excited Upconversion Fluorescence.

Red/near-infrared (NIR) emissive carbon nanodots (CNDs) with photoluminescence (PL) quantum yield (QY) of 57% are prepared via an in situ solvent-free carbonization strategy for the first time. 1-Photon and 2-photon cellular imaging is demonstrated by using the CNDs as red/NIR fluorescence agent due to the high PL QY and low biotoxicity. Further study shows that the red/NIR CNDs exhibit multiphoton excited (MPE) upconversion fluorescence under excitation of 800-2000 nm, which involves three NIR windows (NIR-I, 650-950 nm; NIR-II, 1100-1350; NIR-III, 1600-1870 nm). 2-Photon, 3-photon, and 4-photon excited fluorescence of the CNDs under excitation of different wavelengths is achieved. This study develops an in situ solvent-free carbonization method for efficient red/NIR emissive CNDs with MPE upconversion fluorescence, which may push forward the application of the CNDs in bioimaging.

Supra-(carbon nanodots) with a strong visible to near-infrared absorption band and efficient photothermal conversion.

A novel concept and approach to engineering carbon nanodots (CNDs) were explored to overcome the limited light absorption of CNDs in low-energy spectral regions. In this work, we constructed a novel type of supra-CND by the assembly of surface charge-confined CNDs through possible electrostatic interactions and hydrogen bonding. The resulting supra-CNDs are the first to feature a strong, well-defined absorption band in the visible to near-infrared (NIR) range and to exhibit effective NIR photothermal conversion performance with high photothermal conversion efficiency in excess of 50%.

[Effect of hole transporting materials on photoluminescence of CdSe core/shell quantum dots].

Photoluminescence quenching of colloidal CdSe core/shell quantum dots in the presence of hole transporting materials was studied by means of steady state and time resolved photoluminescence spectroscopy. With increasing hole transporting materials concentration in the CdSe core/shell quantum dot solution, the photoluminescence intensity and lifetime decreased gradually. The photoluminescence quenching of CdSe/ZnSe quantum dots with adding hole transporting material N,N'-bis(1-naphthyl)-N, N'-diphenyl-1,1 '-biphenyl-4, 4'-diamine (NPB) is more efficient than N,N'-diphenyl-N, N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD). And compared with CdSe core/shell quantum dots with ZnSe shell, the ZnS shell is an effective one on the surface of CdSe quantum dots for reducing photoluminescence quenching efficiency when interacting with hole transporting material TPD. Based on the analysis, there are two pathways in the photoluminescence quenching process: static quenching and dynamic quenching. The static quenching results from the decrease in the number of the emitting centers, and the dynamic quenching is caused by the hole transfer from quantum dots to hole transporting materials molecules. The efficiency of the photoluminescence quenching in CdSe core/shell quantum dots is strongly dependent on the structure of the shells and the HOMO levels of the hole transporting materials. The results are important for understanding the nature of quantum dots surface and the interaction of quantum dots and hole transporting materials.