Unraveling Broadband Near-Infrared Luminescence in Cr3+-Doped Ca3Y2Ge3O12 Garnets: Insights from First-Principles Analysis

In this study, we conducted an extensive investigation into broadband near-infrared luminescence of Cr3+-doped Ca3Y2Ge3O12 garnet, employing first-principles calculations within the density functional theory framework. Our initial focus involved determining the site occupancy of Cr3+ activator ions, which revealed a pronounced preference for the Y3+ sites over the Ca2+ and Ge4+ sites, as evidenced by the formation energy calculations. Subsequently, the geometric structures of the excited states 2E and 4T2, along with their optical transition energies relative to the ground state 4A2 in Ca3Y2Ge3O12:Cr3+, were successfully modeled using the ΔSCF method. Calculation convergence challenges were effectively addressed through the proposed fractional particle occupancy schemes. The constructed host-referred binding energy diagram provided a clear description of the luminescence kinetics process in the garnet, which explained the high quantum efficiency of emission. Furthermore, the accurate prediction of thermal excitation energy yielded insights into the thermal stability of the compound, as illustrated in the calculated configuration coordinate diagram. More importantly, all calculated data were consistently aligned with the experimental results. This research not only advances our understanding of the intricate interplay between geometric and electronic structures, optical properties, and thermal behavior in Cr3+-doped garnets but also lays the groundwork for future breakthroughs in the high-throughput design and optimization of luminescent performance and thermal stability in Cr3+-doped phosphors.

Dual substitution of host lattice ions to enhance the luminescence properties of Zn2TiO4:Cr3+ phosphor

Near-infrared light sources have potential applications in many fields. Cr3+ is a good luminescence centre to prepare near-infrared phosphors. Improving the performance of existing near-infrared luminescent materials has indeed attracted great interest from researchers. The luminescence properties of Zn2TiO4:Cr3+ were improved by crystal field engineering strategies. Zn2+-Ti4+ was partially replaced using a Li+-Nb5+ ion pair based on the Zn2TiO4:Cr3+ phosphors. Luminescence Cr3+-activated luminescent materials are sensitive to changes in the local crystal structure and crystal field environment. Doping of Li+-Nb5+ increased the luminescence intensity up to 2.7 times that of the undoped sample. Also, the thermal stability of the phosphor was greatly increased by the replacement of Li+-Nb5+.

Insights into the Superstable Mineralization of Chromium(III) from Wastewater by CuO

The removal of Cr^III ions from contaminated wastewater is of great urgency from both environmental protection and resource utilization perspectives. Herein, we developed a superstable mineralization method to immobilize Cr³⁺ ions from wastewater using CuO as a stabilizer, leading to the formation of a CuCr layered double hydroxide (denoted as CuCr-LDH). CuO showed a superior Cr³⁺ removal performance with a removal efficiency of 97.97% and a maximum adsorption capacity of 207.6 mg/g in a 13000 mg/L Cr³⁺ ion solution. In situ and ex situ X-ray absorption fine structure characterizations were carried out to elucidate the superstable mineralization mechanism. Two reaction pathways were proposed including coprecipitation-dissolution and topological transformation. The mineralized product of CuCr-LDH can be reused for the efficient removal of organic dyes, and the adsorption capacities were up to 248.0 mg/g for Congo red and 240.1 mg/g for Evans blue, respectively. Moreover, CuCr-LDH exhibited a good performance for photocatalytic CO₂ reduction to syngas (H₂/CO = 2.66) with evolution rates of 54.03 μmol/g·h for CO and of 143.94 μmol/g·h for H₂ under λ > 400 nm, respectively. More encouragingly, the actual tanning leather Cr³⁺ wastewater treated by CuO showed that Cr³⁺ can reduce from 3438 to 0.06 mg/L, which was much below discharge standards (1.5 mg/L). This work provides a new approach to the mineralization of Cr³⁺ ions through the "salt-oxide" route, and the findings reported herein may guide the future design of highly efficient mineralization agents for heavy metals.

Interstitial Li+ Occupancy Enabling Radiative/Nonradiative Transition Control toward Highly Efficient Cr3+-Based Near-Infrared Luminescence

Highly efficient and stable broadband near-infrared (NIR) emission phosphors are crucial for the construction of next-generation smart lighting sources; however, the discovery of target phosphors remains a great challenge. Benefiting from the interstitial Li⁺ occupancy-induced relatively large distorted octahedral environment for Cr³⁺ and suppressed nonradiative relaxation of the emission centers, an NIR emission fluoride phosphor Na₃GaF₆:Cr³⁺,Li⁺ peaking at 758 nm with a high internal quantum efficiency of 95.8% and an external quantum efficiency of 38.3% is demonstrated. Moreover, it exhibits a good thermal stability (84.9%@150 °C of the integrated emission intensity at 25 °C) and excellent moisture resistance as well. A high-power light-emitting diode (LED) with a record watt-level NIR output (974.12 mW) and a photoelectric conversion efficiency of 20.9% is demonstrated by combining Na₃GaF₆:Cr³⁺,Li⁺ and a blue InGaN chip, and a special information encryption/decryption technology suitable for rapid and long-distance identification of machines is further presented based on this device. This study not only advances the development of efficient NIR emission phosphors for broadband NIR LEDs but also for NIR-related emerging applications and devices.

A New Cr3+ Electrochemical Sensor Based on ATNA/Nafion/Glassy Carbon Electrode

A new electrochemical sensor of metal cation in an aqueous solution based on homobifunctional tridentate disulfide Schiff base and named 1,1'-(-((disulfanediylbis(2,1-phenylene))bis(azaneylylidene))bis(methaneylylidene))bis(naphthalene-2-ol) (ATNA) was easily obtained quantitatively from the condensation reaction of 2-hydroxy-1-naphthaldehyde and2-aminothiophenol, and then fully characterized by spectroscopic techniques for structure elucidation. The molecular structure of ATNA was also confirmed by a single-crystal X-ray diffraction study to reveal a new conformation in which the molecule was stabilized by the O-H…N type intramolecular hydrogen bonding interactions in both moieties. The ATNA was used as a selective electrochemical sensor for the detection of chromium ion (Cr3+). A thin film of ATNA was coated on to the flat surface of glassy carbon electrode (GCE) followed by 5 % ethanolic Nafion in order to make the modified GCE (ATNA/Nafion/GCE) as an efficient and sensitive electrochemical sensor. It was found to be very effective and selective against Cr3+ cations in the company of other intrusive heavy metal cations such as Al3+, Ce3+, Co2+, Cu2+, Ga3+, Hg2+, Mn2+, Pb2+, and Y3+. The detection limit at 3 S/N was found to be 0.013 nM for Cr3+ ions within the linear dynamic range (LDR) (0.1 nM-10.0 mM) of Cr3+ ions with r2 = 0.9579. Moreover; this work instigates a new methodology for developing the sensitive as well as selective electrochemical toxic cationic sensors in the field of environmental and health care.

A Simple and Rapid Fluorescent Probe for Detection of Cr3+ Based on a Coumarin Schiff Base in Aqueous Solution

A new Cr³⁺ probe was synthesized using simple Schiff base reaction, which showed prominent fluorescence increasing switch before and after addition Cr³⁺. The probe proved to have excellent properties, based on both UV-vis absorption and fluorescence spectra. Those properties included high switching performance, good selectivity, and small interference with other metal ions. The fluorescent change mechanism of the probe was attributed to the combined action between the restricted C=N isomerization and the suppression of highly efficient photo-induced electron transfer (PET) process. Moreover, this fluorescence probe for Cr³⁺ detection also has great potential for bioimaging of cancer cells.