Dye Sensitization for Ultraviolet Upconversion Enhancement

Upconversion nanocrystals that converted near-infrared radiation into emission in the ultraviolet spectral region offer many exciting opportunities for drug release, photocatalysis, photodynamic therapy, and solid-state lasing. However, a key challenge is the development of lanthanide-doped nanocrystals with efficient ultraviolet emission, due to low conversion efficiency. Here, we develop a dye-sensitized, heterogeneous core–multishelled lanthanide nanoparticle for ultraviolet upconversion enhancement. We systematically study the main influencing factors on ultraviolet upconversion emission, including dye concentration, excitation wavelength, and dye-sensitizer distance. Interestingly, our experimental results demonstrate a largely promoted multiphoton upconversion. The underlying mechanism and detailed energy transfer pathway are illustrated. These findings offer insights into future developments of highly ultraviolet-emissive nanohybrids and provide more opportunities for applications in photo-catalysis, biomedicine, and environmental science.

Strain-Tuned Structural, Mechanical and Electronic Properties of Two-Dimensional Transition Metal Sulfides ZrS2: A First Principles Study1

Two-dimensional semiconductor material zirconium disulfide (ZrS2) monolayer is a new promising material with good prospects for nanoscale applications. Recently, a new zirconium disulfide (ZrS2) monolayer with a space group of 59_Pmmn has been successfully predicted. Using first-principles calculations, this new monolayer ZrS2 structure is obtained with stable indirect band gaps of 0.65 eV and 1.46 eV at the DFT-PBE (HSE06) functional levels, respectively. Strain engineering studies on ZrS2 monolayer show effective band gap modulation. The bandgap shows a linear regularity from narrow to wide under applied stresses (strain ranged from − 6% to + 8%). Young's modulus of elasticity of ZrS2 rectangular cells along the tensile directions (x-axis and y-axis) is 83.63 (N/m) and 63.61 (N/m) with Poisson's ratios of 0.09 and 0.07, respectively. The results of carrier mobility show that the electron mobility along the y-axis can reach 1.32×103 cm2V− 1s− 1. Besides, the order of magnitude of the light absorption coefficient in the ultraviolet spectral region is calculated to reach 2.0×105cm−1 for ZrS2 monolayers. Moreover, by regulating the bandgap under stress, some bandgaps of the stretched energy band exceed the free energy of 1.23 eV and possess a suitable energy band edge position. The results indicates that the new two-dimensional Pmmn-ZrS2 monolayer is a potential material for photovoltaic devices and photocatalytic water decomposition.

Оптические свойства квазиобъемных кристаллов нитрида галлия со структурой высокоориентированной текстуры

The results of a study of the optical properties of gallium nitride samples with a highly oriented texture structure grown without the use of traditional semiconductor or sapphire substrates are presented. It is shown that the stacking faults contained in the GaN blocks of the texture of the studied material are self-organized heteropolytype nanostructures, and that the effective luminescence in the ultraviolet spectral region associated with stacking faults I1 in the basal plane is determined by optical transitions of excitons localized near such natural defects in the single-crystalline bulk of the blocks of the GaN texture.

Photoionization of KCs Molecule: Origin of the Structured Continuum?

We report the experimental observation of photoionization bands of the KCs molecule in the deep ultraviolet spectral region between 200 and 420 nm. We discuss the origin of observed photoionization bands as stemming from the absorption from the ground state of the KCs molecule to the excited states of KCs+ molecule for which we used existing potential curves of the KCs+ molecule. An alternative explanation relies on the absorption from the ground state of the KCs molecule to the doubly excited states of the KCs** molecule, situated above the lowest molecular state of KCs+. The relevant potential curves of KCs** are not known yet, but all those KCs** potential curves are certainly autoionizing. However, these two photoionization pathways may interfere resulting in a special interference structured continuum, which is observed as complex bands.