Modulation of Excitonic Confinement of TiO_(2)in Molten Salts for Overall CO_(2)Photoreduction

Excitonic confinement greatly determines the charge carrier transport of photocatalysts.A molten salt modulation of excitonic con-finement is herein demonstrated as formation of ultrafine carbon-doped anatase TiO_(2)with grafted graphitic carbon nitride,which is rationalized as an excellent catalyst for overall CO_(2)photoreduction.Compared with bulk TiO_(2),the carbon-doped TiO_(2)(M-TiO_(2))pos-sesses a weaker excitonic confinement to decrease exciton binding energy from 99 to 58 meV,consequently enhancing free-charge-carrier generation and transportation.Effective Z-scheme electron transfer from M-TiO_(2)to C_(3)N_(4) is built,enhancing the CO_(2)conversion via the synchronous optimization of redox ability,CO_(2)activation,and^(*)COOH generation.This work highlights the unique chemistry of excitonic dissociation on facilitating separation of electron and hole,and also extends the scope of molten salt-mediated modulation of photocatalysis materials.

Optical properties of excitons in strained Ga_x In_1-x As/GaAs quantum dot: effect of geometrical confinement on exciton g-factor

Taking into account anisotropy, nonparabolicity of the conduction band, and geometrical confinement, we discuss the heavy-hole excitonic states in a strained GaxIn1-xAs/GaAs quantum dot for various Ga alloy contents. The strained quantum dot is considered as a spherical InAs dot surrounded by a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and Ga ion content is numerically measured. Interband optical energy with and without the parabolic effect is computed using structural confinement. The interband matrix element for different Ga concentrations is also calculated. The oscillator strength of interband transitions on the dot radius is studied at different Ga concentrations in the GaxIn1-xAs/GaAs quantum dot. Heavy-hole excitonic absorption spectra are recorded for various Ga alloy contents in the GaxIn1-xAs/GaAs quantum dot. Results show that oscillator strength diminishes when dot size decreases because of the dominance of the quantum size effect. Furthermore, exchange enhancement and exchange sDlitting increase as exciton confinement inereases.

Intersubband, interband transitions, and optical properties of two vertically coupled hemispherical quantum dots with wetting layers

The electron and heavy hole energy levels of two vertically coupled In As hemispherical quantum dots/wetting layers embedded in a Ga As barrier are calculated numerically. As the radius increases, the electronic energies increase for the small base radii and decrease for the larger ones. The energies decrease as the dot height increases. The intersubband and interband transitions of the system are also studied. For both, a spectral peak position shift to lower energies is seen due to the vertical coupling of dots. The interband transition energy decreases as the dot size increases, decreases for the dot shapes with larger heights, and reaches a minimum for coupled semisphere dots.