We study the band-edge exciton fine structure and in particular its bright-dark splitting in colloidal semiconductor nanocrystals by four different optical methods based on fluorescence line narrowing and time-resolved measurements at various temperatures down to 2 K. We demonstrate that all these methods provide consistent splitting values and discuss their advances and limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5 monolayers are chosen for experimental demonstrations. The bright-dark splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional to the nanoplatelet thickness. Good agreement between experimental and theoretically calculated size dependence of the bright-dark exciton slitting is achieved. The recombination rates of the bright and dark excitons and the bright to dark relaxation rate are measured by time-resolved techniques.

Three-dimensional (3D) lithiophilic host is one of the most effective ways to regulate the Li dendrites and volume change in working Li metal anode. The state-of-the-art 3D lithiophilic hosts are facing one main challenge in that the lithiophilic layer would melt or fall off in high-temperature environment when using the thermal infusion method. Herein, a 3D porous CuZn alloy host containing anchored lithiophilic Zn sites is employed to prestore Li using the thermal infusion strategy, and a 3D composite Li is thus fabricated. Benefiting from the lithiophilic Zn sites with a strong adsorption capacity with Li, which is based on the analyses of the nucleation overpotential, binding energy calculation, and the operando optical observation of Li plating/stripping behaviors, facile uniform Li nucleation and dendrite-free Li deposition could be achieved in the interior of the 3D porous CuZn alloy host and the 3D composite Li shows remarkable enhancement in electrochemical performance.