Decay time of polaron photoluminescence in congruent lithium niobate

Features of the Defect Structure and Luminescence of Nominally Pure Lithium Niobate Crystals Produced Using Different Technologies

We have established that luminescence in lithium niobate crystals both congruent and near-stoichiometric (R ≈ 1) is due to point defects in the cationic sublattice and intraconfigurational transitions in the oxygen-octahedral NbO₆ clusters. We have also determined that the main contribution to the luminescence in the visible and near IR regions is made by luminescence centers with the participation of Nb_Li defects: the Nb_Li-Nb_Nb bipolaron pair and the Nb_Li-O defect in a congruent crystal. The minimum intensity of bipolaron luminescence has been observed in stoichiometric crystals obtained using different technologies. Weak luminescence of the Nb_Li-Nb_Nb bipolaron pair indicates a small number of Nb_Li defects in the crystal structure. The number of Nb_Li defects in the crystal structure indicates a deviation of the crystal composition from stoichiometry.

Bandgap Engineering in a Staggered-Type Oxide Perovskite Heterojunction for Efficient Visible Light-Driven Photocatalytic Dye Degradation

Oxide perovskite materials with ABO₃ structure have been widely employed for photocatalytic applications. However, owing to the disadvantageous electron-hole recombination process and wide bandgap of some materials, the photocatalytic performance is seemingly restricted. Coupling two catalysts together through the formation of a heterojunction ensures effective charge carrier separation. The intimate interaction between the materials is propitiously useful for charge transfer, thereby increasing the efficacy. In this study, the photocatalytic activity of a K_xNa_(1-x)NbO₃-BaBiO₃ (KNN-BBO) heterojunction material for the degradation of Rhodamine 6G organic dye was investigated. The materials were extensively characterized by X-ray diffraction, UV-Vis diffused reflectance spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and N₂ adsorption isotherms. The degradation efficiency of the organic contaminant under 1 sun simulated sunlight is monitored by spectral analysis from UV-Vis absorption spectroscopy. The resistance to charge transfer was also observed by electrochemical impedance spectroscopy. The effect of the sintering temperature on the photoinduced degradation activity was also included in our study. An unsintered KNN-BBO (UKB) composite material is found to be the most efficient catalyst with 84% removal efficiency as compared to the sintered one (SKB). This is attributed to the reduced bandgap with staggered-type band alignment, increased surface area, and surface oxygen vacancy states. Together with the crucial findings of this work, a probable mechanism for enhanced photocatalytic activity has been proposed here.

Advances in Photocatalytic CO₂ Reduction with Water: A Review

In recent years, the increasing level of CO₂ in the atmosphere has not only contributed to global warming but has also triggered considerable interest in photocatalytic reduction of CO₂. The reduction of CO₂ with H₂O using sunlight is an innovative way to solve the current growing environmental challenges. This paper reviews the basic principles of photocatalysis and photocatalytic CO₂ reduction, discusses the measures of the photocatalytic efficiency and summarizes current advances in the exploration of this technology using different types of semiconductor photocatalysts, such as TiO₂ and modified TiO₂, layered-perovskite Ag/ALa₄Ti₄O₁₅ (A = Ca, Ba, Sr), ferroelectric LiNbO₃, and plasmonic photocatalysts. Visible light harvesting, novel plasmonic photocatalysts offer potential solutions for some of the main drawbacks in this reduction process. Effective plasmonic photocatalysts that have shown reduction activities towards CO₂ with H₂O are highlighted here. Although this technology is still at an embryonic stage, further studies with standard theoretical and comprehensive format are suggested to develop photocatalysts with high production rates and selectivity. Based on the collected results, the immense prospects and opportunities that exist in this technique are also reviewed here.

LiNbO3 coating on concrete surface: a new and environmentally friendly route for artificial photosynthesis

The addition of a photocatalyst to ordinary building materials such as concrete creates environmentally friendly materials by which air pollution or pollution of the surface can be diminished. The use of LiNbO₃ photocatalyst in concrete material would be more beneficial since it can produce artificial photosynthesis in concrete. In these research photoassisted solid-gas phases reduction of carbon dioxide (artificial photosynthesis) was performed using a photocatalyst, LiNbO₃, coated on concrete surface under illumination of UV-visible or sunlight and showed that LiNbO₃ achieved high conversion of CO₂ into products despite the low levels of band-gap light available. The high reaction efficiency of LiNbO₃ is explained by its strong remnant polarization (70 µC/cm²), allowing a longer lifetime of photoinduced carriers as well as an alternative reaction pathway. Due to the ease of usage and good photocatalytic efficiency, the research work done showed its potential application in pollution prevention.

LiNbO3--a new material for artificial photosynthesis

The solid-gas phase photo-assisted reduction of carbon dioxide (artificial photosynthesis) was performed using ferroelectric lithium niobate and titanium dioxide. Illumination with a high-pressure mercury lamp and visible sunlight showed that lithium niobate achieved unexpectedly high conversion of CO(2) to products despite the low levels of band-gap light available. The high reaction efficiency of lithium niobate is explained by its strong remnant polarization (70 μC/cm(2)), allowing a longer lifetime of photo-induced carriers as well as an alternative reaction pathway.