CsPbX₃ (X = Cl, Br, I) perovskite quantum dots (QDs) are an extremely attractive material with a narrow fluorescence peak and tunable emission color by halogen composition. Surface ligands have a variety of effects, including control of size and shape, uniform dispersion through good affinity with solvents and matrices, elimination of quenching sites due to surface defect capping effects and subsequent improvement of luminescent properties, and improvement of stability through surface protection. CsPbX₃ QDs can be synthesized by hot injection and room temperature precipitation methods, using oleic acid (OA) and oleylamine (OLA) as surface ligands. One of the problems with these QDs is their low stability; the mechanism of degradation of QDs is the easy proton transfer between the carboxylate groups of OA and the ammonium groups of OLA on the surface of the QDs, resulting in the desorption of OA and OLA from the QD surface. Ligand desorption creates halogen vacancies, which act as trap levels that cause nonradiative recombination; therefore, it is important to design ligands that hardly desorb from the QD surface to suppress degradation of the QDs. In this talk, we will introduce our results on surface ligand of perfluorocarboxylic acid that improves thermal stability of CsPbBr₃ QDs [1].

Fluorescent carbon quantum dots (CQDs) are attracting attention as an alternative material to toxic QDs. In order to synthesize CQDs with a variety of fluorescent colors, it is effective to select aromatic compounds as carbon sources. The fluorescence color of CQDs changes depending on the polarity of the dispersant. This fluorescence solvatochromism is attributed to the change in the HOMO-LUMO energy gap of CQDs through the dipolar and hydrogen bonding interactions between CQDs and the dispersant molecules. In this talk, we will show that fluorescence solvatochromism of CQDs synthesized from p-phenylenediamine can be modulated by surface modification with perfluorocarboxylic acid [2].

[1] D. Sato, Y. Iso, T. Isobe, ACS Omega, 5, 1178-1187 (2020).

[2] K. Sato, R. Sato, Y. Iso, T. Isobe, Chem. Commun., 56, 2174-2177 (2020).