Recent advances and the current status of challenging light-harvesting nanomaterials, such as semiconducting quantum dots (QDs), metal nanoparticles, semiconductor-metal heterostructures, π-conjugated semiconductor nanoparticles, organic-inorganic heterostructures, and porphyrin-based nanostructures, have been highlighted in this review. The significance of size-, shape-, and composition-dependent exciton decay dynamics and photoinduced energy transfer of QDs is addressed. A fundamental knowledge of these photophysical processes is crucial for the development of efficient light-harvesting systems, like photocatalytic and photovoltaic ones. Again, we have pointed out the impact of the metal-nanoparticle-based surface energy transfer process for developing light-harvesting systems. On the other hand, metal-semiconductor hybrid nanostructures are found to be very promising for photonic applications due to their exciton-plasmon interactions. Potential light-harvesting systems based on dye-doped π-conjugated semiconductor polymer nanoparticles and self-assembled structures of π-conjugated polymer are highlighted. We also discuss the significance of porphyrin-based nanostructures for potential light-harvesting systems. Finally, the future perspective of this research field is given.

Erbium-doped ZrO 2 nanoparticles are prepared by a sol-emulsion-gel technique. The effects of the Er 3+ concentration and different codopants (Yb 3+ and Y 3+ ) in the ZrO 2 matrix on the upconverted emission are reported. Green and red upconversion emission at 550 and 670 nm were observed from these oxide nanocrystals with 980 nm excitation. The overall intensity decreases with an increasing concentration of erbium in zirconia. The presence of codopants (Y 3+ and Yb 3+ ) also increases the overall intensity of the upconverted emission. The emission spectra and the pump intensity dependence of the luminescence intensities are used to understand the excitation mechanism. These results confirm that upconverted emission in these materials is due to a two-photon excited-state absorption (ESA)/energy transfer upconversion (ETU) process.

We demonstrate the surface defect-related luminescence properties of SnO2 nanorods and nanoparticles using steady-state and time-resolved spectroscopy. Defect-related bands are identified by Raman and EPR spectroscopy. On the basis of the experimental results, we propose a schematic model for different relaxation processes in SnO2 nanocrystals upon photoexcitation. Analysis suggests that the visible emission of SnO2 nanocrystals is due to a transition of an electron from a level close to the conduction band edge to a deeply trapped hole in the bulk (V0 ••) of the SnO2 nanocrystals. Analysis suggests that the surface-related defects are more prominent in smaller nanocrystals than in nanorods. It is found that the PL emission and decay time strongly depend on the shape of the nanocrystals. This proposed model is further confirmed by time-resolved spectroscopy.

Doping in carbon nanomaterial with various hetero atoms draws attention due to their tunable properties. Herein, we have synthesized nitrogen containing carbon dots [C-dots (N)], phosphorus co-doped nitrogen containing carbon dots [C-dots (N, P)], and boron co-doped nitrogen containing carbon dots [C-dots (N, B)]; and detailed elemental analysis has been unveiled by X-ray photoelectron spectroscopy (XPS) measurements. Our emphasis is given to understand the effect of doping on the photophysical behavior of carbon dots by using steady-state and time-resolved spectroscopy. Nitrogen containing carbon dots have quantum yield (QY) of 64.0% with an average decay time of 12.8 ns. Photophysical properties (radiative decay rate and average decay time) are found to be increased for phosphorus co-doping carbon dots due to extra electron incorporation for n-type doping (phosphorus dopant) to carbon dots which favors the radiative relaxation pathways. On the contrary, boron (p-type dopant) co-doping with nitrogen containing carbon dots favors the nonradiative electron–hole recombination pathways due to incorporation of excess hole; as a result QY, radiative rate, and average decay time are decreased. To understand the effect of doping on charge transfer phenomena, we have attached nickel (II) phthalocyanine on the surface of C-dots. It is seen that phosphorus co-doping carbon dots accelerates the electron transfer process from carbon dots to phthalocyanine. In contrast, after boron co-doping in carbon dots, the electron transfer process slows down and a simultaneous hole transfer process occurs.

We propose a stochastic model for the kinetics of energy transfer from quantum dots or rods of CdS to Nile Red dye molecules. We assume that the distribution of the dye molecules around quantum dots or rods follows Poisson statistics. By analyzing time-resolved fluorescence decay curves of quantum dots or rods, we obtained the average number of dye molecules attached to the surface of quantum dots or rods as a function of the concentration of dyes and that of quantum dots or rods. The equilibrium constants for attachment/detachment of dye molecules to/from the surface of quantum dots or rods were evaluated. The quenching rate constants per dye molecule attached to the surface of quantum dots or rods were also estimated.