Photoluminescent mechanisms in erbium-doped barium titanate nanoparticle systems were studied. Er³⁺ ions were introduced into the BaTiO₃ lattice by the sol-gel method. The resulting Er³⁺ concentration was between 0% and 5%, with Ba/Ti ratios of 1.008 and 0.993. The stoichiometry of Ba and Ti concentrations in the lattice influenced the doping mechanism and placement of erbium ions in the lattice structure. Our research shows the existence of a strong correlation between Ba/Ti ratios, erbium concentration, phase structure and doping site location on the upconversion photoluminescence mechanisms. Competing upconversion emissions ²H_11/2/⁴S_3/2→⁴I_15/2 at 523 and 548 nm respectively and other photoluminescent mechanisms as ⁴I_9/2→⁴I_11/2 around 4000 nm (2500 cm⁻¹) were studied using Raman and emission spectroscopy. The upconversion process is predominant over other photoluminescent decay when the material presents high distortion in the surrounding activator.

Three photobicyclized benzodithienoquinolizinium tetrafluoroborates (BPDTQBF4) were prepared and evaluated by UV–Vis and fluorescence spectral, electrochemical analysis, and by theoretical calculations as possible organic n-type semiconductors. Evaluation and comparison of their LUMO levels, HOMO-LUMO energy gaps as monomeric and π-stacked dimers with those of other materials, suggest their potential as organic n-type semiconductors. Calculations of their relative charge carrier mobilities confirmed this potential for one derivative with a long (C-14) alkyl chain appended to the polycyclic planar π-system.