Here, we report the dopant concentration and pump-power dependence upconversion emission properties of erbium doped BaTiO₃ nanocrystals derived from sol–emulsion–gel method. Green (550 nm) and red (670 nm) upconversion emissions were observed at room temperature from the ${}^{4}S_{3/2}$ and ${}^{4}F_{9/2}$ levels of Er³⁺ : BaTiO₃ nanocrystals. It is found that at 850 mW of cw excitation power (at 980 nm) the total luminescence was 17130 Cd/m² for 1000°C heated 0.25 mol% Er-doped BaTiO₃ nanocrystals. It is worthwhile to mention that the unusual power-dependent upconversion luminescence (saturation) is observed at higher dopant concentration (2.5 mol%) and high pump power. Our analysis confirms that the depletion of the excited state is responsible for the relevant fluorescence upconversion. We have again confirmed that a twophoton excited state absorption process occurs for all samples.

In this report, we have demonstrated the photoluminescence quenching and energy transfer properties of semiconducting polymer nanoparticles, poly (N-vinylcarbazole) (PVK) in presence of different sized Au nanoparticles by steady state and time-resolved spectroscopy. We have described the quenching phenomena by sphere of action static quenching mechanism and both dynamic and static quenching processes are found in these systems. PL quenching values are 24.22% and 57.3% for 14 nm and 18 nm Au nanoparticles, respectively. It is found that the radiative and nonradiative decay have been modified with the size of Au nanoparticles. PL quenching and shortening of decay time regarding polymer nanoparticles in presence of Au nanoparticles suggest the nonradiative energy transfer process. The values of energy transfer are 6.7%, 49.5% and 53.38% from PVK polymer nanoparticles to 3 nm, 14 nm and 18 nm Au nanoparticles, respectively. Using FRET and SET equations we have calculated the average distance of donor PVK polymer nanoparticles and acceptor Au nanoparticles.

Design of highly luminescent nanomaterials is an emerging area of research for photonic and bio-photonic applications. Nowadays, dye-encapsulated polymer nanoparticles (PNPs) are found to be very promising alternative nextgenerationluminescent nanomaterials because of extraordinary brightness, easy synthesis, higher photo-stability and nontoxic behaviour. Herein, we have highlighted the dynamics of the fluorophore molecules inside PNPs. Furthermore, we discuss the fundamental correlation of particle brightness with the size of the PNPs as well as population of the dye molecules inside the PNPs. Considering the resonance energy transfer process, generation of white light by varying the dye concentration and singlet oxygen generation using photosensitizer dye have been described. Finally, we discuss the importance of hybrids of conjugated PNPs for potential light harvesting systems such as photovoltaic and optoelectronic applications.

Exciton generation, migration and dissociation are key fundamental processes that dictate the efficiency of optoelectronic devices. Here, we investigate exciton diffusion process of conjugated polymer nanoparticles (PNPs) in the presence of electron and hole scavenger molecules using time-resolved spectroscopy. We found that the exciton diffusion length of hole transporting PNPs, decreases in the presence of hole scavenger molecule and it increases in the presence of electron scavenger molecule. Analysis reveals that the diffusivity of excitons can be controlled by changing the nature of scavenger molecules. Such fundamental study is important for developing devices where lower and higher exciton diffusivities are required depending on the requirement of application mode.