Different Upconversion Properties of β‑NaYF₄:Yb³⁺,Tm³⁺/Er³⁺ in Affecting the Near-Infrared-Driven Photocatalytic Activity of High-Reactive TiO₂

Double-shell-structured β-NaYF₄:Yb³⁺,Tm³⁺/Er³⁺@SiO₂@TiO₂ upconversion photocatalysts have been successfully synthesized by a simple hydrothermal method. It is found that the double-shell-structured photocatalyst consists of uniform β-NaYF₄:Yb³⁺,Tm³⁺/Er³⁺ nanocrystals, SiO₂ as the media shell, and anatase TiO₂ nanocrystals exposed with the high-reactive {001} facets as the outer shell. The TiO₂ shell is modified to absorb both the UV and visible light in order to make sufficient use of the upconverted light from β-NaYF₄:Yb³⁺,Tm³⁺/Er³⁺ for photocatalysis. Effective energy transfer from β-NaYF₄:Yb³⁺,Tm³⁺/Er³⁺ to TiO₂ and its importance are confirmed. The photocatalytic activity in the degradation of Rhodamine B (RhB) under the near-infrared (NIR) (980 nm laser) irradiation suggests that the NIR-driven photocatalytic activity of the double-shell-structured photocatalyst is significantly dependent on the properties of the upconversion materials and the irradiated NIR power density. Moreover, the NIR-driven photocatalyst shows stable photocatalytic degradation of RhB in the recycled tests. This study suggests a promising system and a new insight to understand the application of appropriate upconversion materials to effectively utilize the NIR for photocatalytic applications of TiO₂-based photocatalysts, which may advance the application of solar energy in the future

Near-Infrared Upconversion Transparent Inorganic Nanofilm: Confined-Space Directed Oriented Crystal Growth and Distinctive Ultraviolet Emission

A well-designed, efficient, one-step assembly strategy is implemented in this work by constructing a confined nanospace to manufacture an approximately 120 nm thick inorganic upconversion (UC) nanofilm with highly (101) oriented and morphology-controllable crystal grains, as well as transparent and robust characteristics. The morphology and distribution density of crystal grains of the film can be tuned by varying space heights and precursor concentrations. The confined space incubates a stable growing environment for crystal grains to decrease crystal defects and grow bigger. Therefore, there are high populations of doped Tm ions and high efficiencies of radiation transitions to realize multiphotons ultraviolet (UV) (monitoring range: 300–400 nm) emissions under laser excitation with a wide power range. Quantum yields of the film in the UV region are 4.7 and 16.1 times higher than those of UC nanoparticles synthesized by the typical thermal decomposition method and hydrothermal method, respectively. The UV-enhanced UC film is demonstrated to have the ability to serve as a medium to realize near-infrared induced undersurface photochemical reactions, which may inspire broad applications, such as UC three-dimensional printing

Oriented Built-in Electric Field Introduced by Surface Gradient Diffusion Doping for Enhanced Photocatalytic H₂ Evolution in CdS Nanorods

Element doping has been extensively attempted to develop visible-light-driven photocatalysts, which introduces impurity levels and enhances light absorption. However, the dopants can also become recombination centers for photogenerated electrons and holes. To address the recombination challenge, we report a gradient phosphorus-doped CdS (CdS-P) homojunction nanostructure, creating an oriented built-in electric-field for efficient extraction of carriers from inside to surface of the photocatalyst. The apparent quantum efficiency (AQY) based on the cocatalyst-free photocatalyst is up to 8.2% at 420 nm while the H₂ evolution rate boosts to 194.3 μmol·h^–1·mg^–1, which is 58.3 times higher than that of pristine CdS. This concept of oriented built-in electric field introduced by surface gradient diffusion doping should provide a new approach to design other types of semiconductor photocatalysts for efficient solar-to-chemical conversion

Oriented Built-in Electric Field Introduced by Surface Gradient Diffusion Doping for Enhanced Photocatalytic H₂ Evolution in CdS Nanorods

Element doping has been extensively attempted to develop visible-light-driven photocatalysts, which introduces impurity levels and enhances light absorption. However, the dopants can also become recombination centers for photogenerated electrons and holes. To address the recombination challenge, we report a gradient phosphorus-doped CdS (CdS-P) homojunction nanostructure, creating an oriented built-in electric-field for efficient extraction of carriers from inside to surface of the photocatalyst. The apparent quantum efficiency (AQY) based on the cocatalyst-free photocatalyst is up to 8.2% at 420 nm while the H₂ evolution rate boosts to 194.3 μmol·h^–1·mg^–1, which is 58.3 times higher than that of pristine CdS. This concept of oriented built-in electric field introduced by surface gradient diffusion doping should provide a new approach to design other types of semiconductor photocatalysts for efficient solar-to-chemical conversion