We present a general hydrothermal method without any organic solvent or surfactant for the synthesis of YBO₃:Eu³⁺ nano- and micro-structures. The samples were of excellent quality with uniform, well dispersed, self-assembled and self-purified YBO₃:Eu³⁺. Single crystal nanoflakes gathered together to evolve into a hierarchical architecture with eight different types of three dimensional morphologies. Strong photoluminescence spectra were obtained at 592, 611 and 627 nm at excitations wavelengths 254 and 363 nm. The emission spectra are associated with the transitions from the excited ⁵D₀ level to the ⁷F_J (J = 1, 2, 3, 4) levels of Eu³⁺ activators. YBO₃:Eu³⁺ prepared using ethanol solvent exhibited the highest chromaticity values yet reported.

Structural and optical studies are reported of yttrium orthoborate YBO₃ when tri-doped with Eu³⁺, Ce³⁺, and Tb³⁺, focusing on the role of terbium concentration. Incorporation of Tb³⁺ affects emission properties for photoluminescence (PL) excited by near ultraviolet light. For constant cerium and europium concentrations, increasing the Tb³⁺ results in diminished PL from the Ce³⁺ and Tb³⁺ color centers. Simultaneously, the PL excitation bands related to both Ce³⁺ and Tb³⁺ increase in intensity for red emission from the Eu³⁺. Results are consistent with a Ce³⁺ → (Tb³⁺)_n → Eu³⁺ energy transfer scheme, where (Tb³⁺)_n denotes a chain incorporating n terbium ions. A high red to orange PL intensity ratio is obtained, ranging from 1.34 to 2.09. Raman vibrational bands show a systematic change, with Tb³⁺ concentration, in the B₃O₉ ring terminal oxygen bending mode coordinated with the yttrium site where dopant ions substitute. The structural changes are interpreted as variations in the local neighborhood of these sites in the YBO₃:Ce³⁺,Tb³⁺,Eu³⁺ crystal structure.

Heterostructures with CdTe and CdTe_1-xSe_x (x ∼ 0.01) absorbers between two wider-band-gap Cd_1-xMg_xTe barriers (x ∼ 0.25–0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ∼6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.

The nucleation and growth of organic–inorganic hybrid perovskite films induced by the molar ratio of precursor components and their role in optoelectronic performance are investigated. Lead iodide (PbI₂), methylammonium acetate (MAAc) and methylammonium iodide (MAI) mixed in different ratios were used as starting precursors for active layer deposition. While all the as cast films showed the presence of a precursor intermediate (PbI_x·MAAc·MAI), the films derived from 1 : 1 : 1 and 1 : 0.5 : 1 ratios also exhibited crystallization of the perovskite (CH₃NH₃PbI₃) phase during the spin coating process. The nucleation and crystallization of the perovskite phase in films derived from the equimolar precursor ratio were found to be the key to growing larger, smoother and single crystalline grains along the thickness leading to higher carrier lifetimes. Perovskite solar cells fabricated utilizing such a morphology showed a much higher power conversion efficiency irrespective of the active layer thickness. Furthermore, methyl ammonium bromide based perovskite light emitting diodes were also fabricated using the aforementioned equimolar precursor ratio which exhibited superior device performance compared to diodes with active layers derived from other precursor ratios. This work highlights a facile deposition technique and growth mechanism to attain reproducible, low cost and high-performance perovskite optoelectronic devices.