Here we present a facile aqueous approach to synthesize heterostructured CdSe/CdS QDs with all-inorganic chalcogenide S²⁻ ligands under mild conditions. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and steady-state emission spectroscopy demonstrate that the heterostructured CdSe/CdS QDs with sulfur-rich surface composition are formed by heterogeneous nucleation of Cd²⁺ and S²⁻ precursors on the CdSe QDs. After adsorption of small Ni(OH)₂ clusters over the surface in situ, the CdSe/CdS–Ni(OH)₂ photocatalyst enables H₂ production efficiently with an internal quantum yield of 52% under visible light irradiation at 455 nm, up to an 8-fold increase of activity to that of spherical CdSe QDs–Ni(OH)₂ under the same conditions. Femtosecond transient absorption spectroscopy, X-ray transient absorption (XTA) spectroscopy, steady-state and time-resolved emission spectroscopy show that the quasi-type-II band alignment in the CdSe/CdS heterostructure is responsible for the efficiency enhancement of light harvesting and surface/interfacial charge separation in solar energy conversion. The unprecedented results exemplify an easily accessible pattern of aqueous synthesis of all-inorganic heterostructured QDs for advanced photosynthetic H₂ evolution.

Concentration quenching of rare-earth doped upconversion nanoparticles severely limits the dopant concentration, and this greatly hinders their potential applications. Therefore, it is necessary to understand the roles of dopant concentration in photon population and luminescence quenching for materials designed with improved upconversion luminescence (UCL). Herein, the excited-state dynamics of well-accepted NaYF₄:Yb³⁺,Er³⁺ nanocrystals were investigated as models based on the Kohlrausch-function. The use of the Kohlrausch-function successfully disentangled the rise and decay of dynamics data and well revealed the kinetics. Photon population and concentration quenching mechanisms depending on the sensitizer concentration are deeply revealed by the regular variations of the fitting parameters. The results indicated that high doping of sensitizers will accelerate the population of both green and red emitting energy levels, but cause significant concentration quenching in green emission and little quenching in red emission. Our work opened up new pathways of kinetics analysis, which is beneficial for further mechanism development, and established detailed photon population and concentration quenching models depending on the doping concentration of the sensitizer.