CsPb(Br,I) 3 quantum dots (QDs) show application potential for optoelectronic devices. However, their thermal degradation is a significant problem. In this work, the effects of perfluorodecanoic acid (PFDA) modification on the photoluminescence (PL) and thermal resistance of CsPb(Br,I) 3 QDs were evaluated. The PL intensity of oleic-acid-modified quantum dots (OA-QDs) in toluene decreased drastically upon heating at 100°C. The PL quantum yield of the QDs increased from 69.6% to 77.4% upon modification with PFDA. Furthermore, the PL intensity of the QDs modified with PFDA (PFDA-QDs) increased to 140.6% upon heating, because of the reduction of surface defects upon adsorption of PFDA and its optimized adsorption state. A solid-film PFDA-QDs sample heated at 80°C for 4 h showed temporary PL enhancements for the OA-QDs and PFDA-QDs films to 445% and 557% of their initial values, respectively, upon heating for 0.25 h. This was attributed to the optimized adsorption states of the surface ligands. PFDA-QDs film maintained 354% after 4 h of heating, whereas that of OA-QDs film was 104%. Thus, PFDA modification enhances PL intensity and suppresses PL degradation under heating, which is important for wavelength converters for optoelectronic device applications.

Photoinduced desorption of surface ligands causes photodegradation of nanophosphors due to enhanced non-radiative relaxation, which is attributed to generated surface defects. We previously reported the self-recovery of photodegraded CsPbBr3 nanocrystals (NCs) and revealed that its mechanism can be attributed to readsorption of the desorbed surface ligands. Thus, using different surface ligands would change the photodegradation and subsequent self-recovery behaviors. Accordingly, in the present work, perfluorodecanoic acid (PFDA) was added to pre-synthesized CsPbBr3 NCs modified with oleic acid and oleylamine to evaluate its effects on photodegradation and subsequent self-recovery. The as-prepared NCs (OA-NCs) and PFDA-modified NCs (PFDA-NCs) were dispersed in nanocomposite ethylene-vinyl acetate resin films to suppress concentration quenching. OA-NCs showed monotonical photoluminescence (PL) decrease under blue excitation light and self-recovery during subsequent dark storage. In contrast, the PFDA-NCs exhibited temporary PL enhancement under excitation irradiation. The photo-activation is attributed to optimization of the adsorption states of the surface ligands in the early stage, while the influence of photodegradation due to ligand desorption becomes dominant later. However, increased PFDA modification prevented self-recovery, indicating that desorbed PFDA may be resistant to readsorption on the NC surface.