Transition Metal Ion Doping Research Articles

Nonlinear Photonics Using Low‐Dimensional Metal‐Halide Perovskites: Recent Advances and Future Challenges

Low-dimensional metal-halide perovskites have exhibited significantly superior nonlinear optical properties compared to traditional semiconductor counterparts, thanks to their peculiar physical and electronic structures. Their exceptional nonlinear optical characteristics make them excellent candidates for revolutionizing widespread applications. However, the research of nonlinear photonics based on low-dimensional metal-halide perovskites is in its infancy. There is a lack of comprehensive and in-depth summary of this research realm. Here, the state-of-the-art research progress related to third-and higher-order nonlinear optical properties of low-dimensional metal-halide perovskites with diverse crystal structures from 3D down to 0D, together with their practical applications, is summarized comprehensively. Critical discussions are offered on thefundamental mechanisms beneath their exceptional nonlinear optical performancefrom the physics viewpoint, attempting to disclose the role of intrinsic attributes (e.g., composition, bandgap, size, shape, and structure) and external modulation strategies (e.g., developing core-shell structures, transition metal ion doping, and hybridization with dielectric microspheres) in tuning the response. Additionally, their potential applications in nonlinear photonics, nonlinear optoelectronics, and biophotonics are systematically and thoroughly summed up and categorized. Lastly, insights into the current technical challenges and future research opportunities of nonlinear photonics based on low-dimensional metal-halide perovskites are provided.

Transition metal ion-doped In2O3 nanocubes: investigation of their photocatalytic degradation activity under sunlight.

The objective of this work was to study the effect of transition metal ion doping (1 wt% of Mn, Fe, Co, Ni, and Cu) in indium oxide (In2O3) on its photocatalytic activity to degrade organic dyes, which are considered potential environment pollutants. The transition metal ion-doped In2O3 nanocube photocatalyst was prepared via the hydrothermal method. After understanding the thermal behavior of the as-prepared sample (In(OH)3), it was calcined at 400 °C for 3 h to obtain In2O3. The In2O3 was systematically investigated via FESEM, X-ray diffraction, Raman spectroscopy and UV-vis absorption analysis. Microstructure analysis by FESEM showed that the In2O3 was formed as nanocubes. These nanocubes were formed in a single phase with a cubic crystal structure, while their crystallite size increased from 11 nm to 19 nm when doped with 1 wt% of transition metals, including Mn, Fe, Co, Ni and Cu. The band gap energy for pure In2O3 was determined to be 3 eV, and that for the metal ion-doped In2O3 showed a slight decrease to the lowest value of 2.94 eV. The photoluminescence (PL) decay lifetime was found to be in the range of 28.56 ns to 33.89 ns. Photocatalytic experiments were conducted for the degradation of methylene blue (MB) dye under sunlight irradiation in the presence of the In2O3 nanocubes. Among the five metal ion-doped samples, the Ni ion-doped In2O3 photocatalyst exhibited the highest degradation efficiency of 98% in 270 min of sunlight exposure. The high performance of Ni–In2O3 is due to its highest PL lifetime of 33.89 ns. The complete route for the degradation of MB dye was revealed by identifying the intermediates.

Evaluation of physical and radiation shielding properties of Bi2O3–B2O3 glass doped transition metals ions

Bismuth borate glasses of formula 60% Bi2O3 and 40% B2O3 doped 0.7 wt % of one of the transition metal oxides; TiO2, Cr2O3, V2O5 or Fe2O3 were prepared using melting-annealing method. The glasses optical transmittance spectra have been studied and reveal UV transmission bands related to the different valence states of the doped transition metal ions. Electrical conductivity and many physical parameters of the glasses were also investigated such as; optical bandgap (Eopt), refractive index (n), reflection loss (RL), molar refractivity (Rm), molar polarizability (αm), dielectric constants (ε), optical transmission coefficient (T) and metallization criterion (M Criterion).The effectiveness of the glasses as radiation protective shield was evaluated and calculated by Monte Carlo N-Particle Transport Code (MCNP) using the Medical Internal Radiation Dose (MIRD) of male human model. Many shielding parameters have been also deliberated such as; linear attenuation coefficient, effective removal cross section (ΣR), radiation protective efficiency (RPE %), tissue weighting factors (Wt), in addition to a comparison between the experimental and the simulated linear gamma attenuation coefficients at numerous energies. The glasses reveal high stable optical and physical properties in addition to high radiation shielding efficiency against gamma irradiation. The high concentration of heavy Bi3+ ions and presence of transition metal ions with their variable configurations, provide the shielding behavior of the glasses and decreased the life time risk for cancer by about five times.

Stable near white light emission in CsPbCl3 perovskite quantum dots by incorporating Al3+/Mn2+ ions

All inorganic cesium lead halides (CsPbX3, X = Cl, Br, I) are promising materials and have been developed in recent years for various optoelectronic devices and applications because of their excellent optoelectronic properties. Regardless of their excellent characteristics their stability is still uncertain and it is challenging task to obtain stable emission in CsPbX3 perovskite quantum dots (PQDs), hence limiting their practical optoelectronic application. In this context, several approaches have been used like an-ion exchange, ion doping, and core–shell structure to enhance PQDs stability. Herein, we synthesized dual ion co-doped Al3+/Mn2+ CsPbCl3 PQDs for stable light emitting diodes through traditional hot injection method for the first time. By adjusting molar concentration of Al3+/Mn2+ CsPbCl3, co-doped PQDs were successfully prepared. The co-doped PQDs exhibit tunable emission, covering a wide range under UV excitation. Moreover, these high luminescent co-doped PQDs were used to fabricate WLEDs, displaying stable near white light emission with the chromaticity coordination at (0.35, 0.28). Some new evidence has emerged, although some aspects of Mn2+ and Al3+ doping are considered to be consistent with previous conclusions. This viewpoint incorporates all of these details and focuses on the path of transition metal ion doping to perovskite nanostructures and offers an overview for possible potential studies.

An investigation of local structures for 3d3, 3d5 and 3d7 ions doing in the layered LiCoO2 cathode materials

Doping transition metal ions in LiCoO2 batteries has been proved an efficient method to improve the electrochemical properties in experiment, which is deeply related with the distorted local structure of impurities ions. According to the observed EPR spectra, the distorted local structures for 3d3 (Mn4+), 3d5 (Fe3+) and 3d7 (Ni3+) ions in LiCoO2 batteries are theoretically studied based on the perturbation calculations of Spin Hamilton Parameters (g factors, hyperfine structure constants A and Zero-field splittings parameters D and E). By considering the Jahn-Teller effect and mismatch radius of above transition metal ions (TMs), the formed [MnO6]8-, [FeO6]9- and [NiO6]9- clusters in LiCoO2 exhibit various distorted symmetries compared with experimental single one, characterized by trigonal distortion parameter Δθ as well as rhombic distortion parameters ΔZ and Δϕ in the 3d3 center and the 3d5 center and tetragonal distortion parameter ΔZ in the 3d7 center. In addition, compared with asymmetrical signal of EPR spectra at 30K, the role of relatively high temperature for 100K is investigated by dynamic Jahn-Teller, making the isotropic EPR signal and regular octahedron for Ni3+ center. Comparing with the obtained structure properties of isolate-doped transition metal ion, the co-doped Mg in LiCoO2 makes the further elongated distortion of local structure. Based on the well fitted EPR parameters and obtained local environment of doped transition metal ions, the inactive of electrochemical properties of Mn4+ can be attribute to the largest crystal field (Dq) and the smallest difference with host Co3+ site. Therefore, a comprehensively study of the local structure may be helpful to understand and predict the electrochemical behaviors of batteries.

Trapped excited electrons in Ni2+-doped perovskite KZnF3 nanocrystals in KF-ZnF2-SiO2 glass ceramics.

The photonic properties of glass ceramics (GCs) are often enabled by encapsulating nanocrystals (NCs) and doped transition metal ions (TMIs). However, it is difficult to probe the optics-related effect between the host NCs' band structure and doped TMIs' d-d orbitals. Herein, perovskite-type KZnF3:NiNCs in KF-ZnF2-SiO2 GCs were prepared and taken as a model system. The excited-state dynamics of host NCs and Ni ions' d-d orbitals were studied by transient absorption spectroscopy. It presents a strong interaction between Ni's d orbitals and the band edge, which could extract excitonic energy in photonic applications. These findings facilitate understanding and design of TMIs-doped GCs in real-life photonic applications.

Non-lanthanide activated red emission in CdAl2O4 phosphors with nanotube type crystal structure

Abstract Rare earth-doped phosphors have great potential in various applications. Given the cost issue confronting the rare earth ions, the doping of transition metal ions provides a cost-effective approach for realizing the light emitting. In this paper, using CdAl2O4 as the host, red emission through Fe3+ ions has been demonstrated. CdAl2O4:Fe3+ shows the strong red emission at around 700 nm, attributing to the 4T1(4G) to 6A1(6S) transitions of Fe3+ ions. Moreover, the intensity dependence of such a red emission on the Fe3+ doping is quantitatively analyzed, and the optimized doping concentration is 0.015. Band structure calculation indicates that Fe3+ doping can widen the light absorption range of CdAl2O4 host via doping the Fe3+ ions. The efficient luminescence can be elucidated by the synergistic effect of electrons in Fe3+ ions and nanotube-type host lattice. Furthermore, on the basis of these findings, we developed Cr3+-doped red emission phosphors. Moreover, a red LED is successfully fabricated via combination Cr3+-doped CdAl2O4 phosphors with near UV LED ships. The successful realization of red lighting via Fe3+ or Cr3+ ions provides a new perspective for the development of luminescent materials, thereby initiating the non-rare-earth based phosphors for light emitting diodes and displays applications.

Low temperature synthesis of wurtzite form of ZnS from single source precursor

Wurtzite form of ZnS has been prepared by heating zinc ethane thiol complex at a relatively low temperature of less than 300 °C. This low temperature synthesized, high temperature form of ZnS is quite stable and does not undergo conversion to cubic form even at annealing temperatures as high as 900 °C. The “c/a” ratio of ZnS lattice decreases whereas average crystallite size and “I(hkl)/I(002)” ratio increase with increase in annealing temperatures up to 700 °C and remains same for samples heated at 800 and 900 °C. Although crystallite sizes remain same for 800 and 900 °C heated samples, carbon species get removed from the lattice with increase in annealing temperatures and this is further confirmed by decrease in value of strain, FTIR and luminescence results. The synthesis method also can be used for doping transition metal ions such as Mn2+ in ZnS lattice. EPR Studies confirmed incorporation of Mn2+ ions at Zn2+ site in ZnS lattice.

Modulating Charge-Carrier Dynamics in Mn-Doped All-Inorganic Halide Perovskite Quantum Dots through the Doping-Induced Deep Trap States.

Transition-metal ion doping has been demonstrated to be effective for tuning the photoluminescence properties of perovskite quantum dots (QDs). However, it would inevitably introduce defects in the lattice. As the Mn concentration increases, the Mn dopant photoluminescence quantum yield (PLQY) first increases and then decreases. Herein the influence of the dopant and the defect states on the photophysics in Mn-doped CsPbCl3 QDs was studied by time-resolved spectroscopies, whereas the energy levels of the possible defect states were analyzed by density functional theory calculations. We reveal the formation of deep interstitials defects (Cli) by Mn2+ doping. The depopulation of initial QD exciton states is a competition between exciton-dopant energy transfer and defect trapping on an early time scale (<100 ps), which determines the final PLQY of the QDs. The present work establishes a robust material optimization guideline for all of the emerging applications where a high PLQY is essential.

Anodic oxidation growth of lanthanum/manganese-doped TiO2 nanotube arrays for photocatalytic degradation of various organic dyes

Lanthanum/manganese-doped TiO2 nanotube arrays (La/Mn-TNAs) can provide a greater catalytic area and possess stronger photocatalytic activity than TiO2 nanotubes (Li et al. in Nano Res 8(3):900–906, (2015)). Due to the wide band gap, TiO2′s capacity to capture visible light is low, and TiO2 (3.2 eV) can only absorb ultraviolet light. To resolve this issue, most researchers doped TiO2 with nitrogen. In this paper, we doped transition metal ions and rare earth metal ions in TiO2 nanotube arrays to decrease their band gaps, improving the activities of photocatalysts. In addition, La/Mn-TNAs were obtained by anodizing a Ti foil in the electrolyte. Additionally, the photocatalytic activity of the sample was evaluated by analyzing the degradation rate of organic pollutants. As a result, when the Ti foil was anodic oxidation for 3 h and contained 4.8 wt% of lanthanum and manganese, it could degrade organic dyes entirely in 60 min and the degradation rate of organic dyes was over 95%. Thus, La/Mn-TNAs can satisfy people’s requirement of rapid degradation of organic pollutants.

Atomic deciphering of cation exchange mechanism in upconversion nanoparticles

Transition metal ion doping in upconversion nanoparticles (UCNPs) provides an effective way to enhance the luminescence for their wide array of applications. However, the doping sites of transition metal ions have not been comprehensively explored, and commonly assumed that transition metal ions replace the trivalent lanthanides within the lattice. Here we report that cation exchange of transition metal (Mn2+) in β-NaYF4:Yb3+/Er3+ UCNPs occurs through alkaline metal (Na+) replacement, via 2Na+↔ Mn2+ + Vacancy reaction. This process distorts the LnF9 polyhedrons and tailors the surrounding environment around the trivalent lanthanides, thereby improving the upconversion intensity from active lanthanides. Further confirmed by core-shell design and spectroscopic study, we prove that the transition–alkaline metal exchange enables both the emission enhancement and transition probability variation of activators.

Recent processes on light-emitting lead-free metal halide perovskites

Lead halide perovskites (LHPs) have great potential applications in light-emitting diodes (LEDs) for advanced displays and general lighting due to their excellent optical and electrical properties. However, LHPs suffer from toxicity and poor stability. Although the stability of the perovskites can be enhanced by reducing dimensionality, doping transition metal ions, encapsulating organic polymers, or building super-hydrophobic structures, the improved stability is limited and still cannot meet the needs for practical applications. To fundamentally solve the above issues, lead-free metal halide perovskites (LFMHPs) have been alternatively developed owing to their low toxicity, expected good stability and excellent optical properties. In this review, we thoroughly overview recent processes on the synthetic method, type, structure, morphology, and optical properties of LFMHPs with a strict perovskite structure as well as on their stabilities against water, light, or heat. We further highlight their preliminary achievements in display and lighting applications. Finally, we address remaining challenges in this exciting field and present our perspectives for further investigations on LFMHPs to enhance the performance and lifetime of LED devices.

Cu(II) and Gd(III) doped boehmite nanostructures: a comparative study of electrical property and thermal stability

The present article reports the effect of transition (Cu2+) and rare earth metal (Gd3+) ion doping on structural, microstructural and electrical properties of boehmite nanoparticles. Rietveld refinement is adopted here to refine the x-ray diffractograms for further analyzing the microstructural details and their alteration due to the incorporation of foreign cations. This is probably the first time when dielectric properties of these doped boehmite samples having been reported herein. These samples show remarkably high dielectric constant values which corroborate that doping enhances the microstrain values inside the orthorhombic structure and results in higher crystallographic defects. Enhancement in defect sites causes the augmentation of relative permittivity and ac conductivity. Temperature stability has also been enhanced significantly in our Cu-doped sample. The present study enables us to determine a relationship between crystalline deformation and electrical properties of nanomaterials which may be highly beneficial in fabricating cost-effective energy harvesting devices.

Visible light photocatalytic activity of metal (Mo/V/W) doped porous TiO2 coating fabricated on Cp-Ti by plasma electrolytic oxidation

Photocatalytic degradation under visible light region acquired a wide interest in the field of wastewater treatment. In this study, the transition metal ion (Mo/V/W) doped TiO2 layer was developed on commercially pure titanium (Cp-Ti), by plasma electrolytic oxidation (PEO), as an immobilized photocatalytic surface for textile wastewater treatment application. The effect of transition metal ion (Mo/V/W) doping on TiO2 coating phase composition, surface morphology, corrosion, wettability, bandgap, charge separation and electron-hole recombination rate are investigated. The phase analysis of coatings showed that the dopants suppressed the formation of the rutile. The doped TiO2 samples exhibited higher surface porosity and active surface area, thereby enhancing the photocatalytic activity. Among the doped titanium oxides, W doped TiO2 exhibited superior charge separation with 95% degradation and 71% mineralisation of methylene blue dye under visible light irradiation for 180 min. This could be attributed to the synergistic effect of lower bandgap, high charge separation, and low electron-hole recombination rate. The present research positively demonstrated an efficient, visible light driven immobilized photo catalyst surface by a simple PEO process as a promising photocatalytic system in the quest for the development of low cost and sustainable process for textile wastewater treatment application.

Cr doped-Co9S8 nanoarrays as high-efficiency electrocatalysts for water splitting

Doping transition metal ions into Co9S8 has received extensive attention as an electrocatalyst for water splitting. In this paper, Density functional theory (DFT) calculation is supposed to assess the water adsorption energy of M (M = 1-Cr, 3-Cr and 6-Cr) doped CoxS8 to better predict the water oxidation activity of all the synthetic materials and synergistic reaction mechanism between the content of doped Cr ion and cobalt ion. A series of Cr-CoxS8 materials are firstly prepared by simple hydrothermal and sulfuration process. It is worth noting that only 1.45 V cell voltage is required to generate 10 mA cm−2 current density during the whole water splitting, which is one of the smallest cell voltages reported. The experimental results are highly consistent with theoretical predictions. The excellent electrochemical activity of Cr3–Co6S8/NF is mainly ascribed to the following factors: firstly, the presence of Cr3+ enhances the chemisorption free energy of water and the metallic nature of the material. Secondly, the rough surface around the honeycomb nanoarrays further improves the reaction surface area and promotes mass transfer rate. The work offers a new insight for developing an environmentally friendly and robust electrocatalyst for large-scale water splitting applications.

Enhanced water oxidation performances of birnessite and magnetic birnessite nanocomposites by transition metal ion doping

Co2+ and Ni2+ doped layered birnessite and birnessite-manganese ferrite core–shell catalysts displayed enhanced chemical stability and performance in chemical and electrochemical water oxidation reactions.

Transition metal doped ZnO nanoparticles with enhanced photocatalytic and antibacterial performances: Experimental and DFT studies

Transition metal doped ZnO (TM-ZnO) nanoparticles with 3% dopant content are successfully prepared via a simple solvothermal route. This work highlights Mn, Fe, Co, Ni or Cu ions as the dopant transition metals. The as-prepared samples are wurtzite phase ZnO crystals, and the average sizes of undoped ZnO and TM-ZnO nanoparticles range from 200 nm to 400 nm. XPS studies confirm that the transition metal ions are successfully doped into the crystal lattice of ZnO. The band gaps of the undoped ZnO and TM-ZnO crystals are calculated by using UV-DRS spectroscopic measurements. The visible light response of ZnO nanomaterials is improved by doping transition metal ions. For investigating the influence of transition metal doping on the photocatalytic performance of ZnO, the photodegradation rate of methylene blue (MB) is investigated under simulated sunlight irradiation. The photocatalytic properties of ZnO doped with transition metals are improved at different degrees, among which Cu-doped ZnO exhibits the best photocatalytic performance. Based on density functional theory (DFT) calculation result, a possible photocatalytic mechanism is proposed. Furthermore, the antibacterial performance of Cu-doped ZnO is investigated by selecting E. coli, under simulated sunlight irradiation and remarkable sterilization of E. coli is achieved.

Transition-Metal-Ion (Fe, Co, Cr, Mn, Etc.) Doping of TiO2 Nanotubes: A General Approach.

Transition-metal (TM)-ion-doped TiO2 materials are of great importance for photocatalysis- and photoelectrochemical (PEC)-related applications. We introduced a facile, low-cost, and scalable doping method of TM ions (Cr, Co, Cu, Fe, Mn, etc.) into TiO2 nanotubes (NTs), while maintaining their high-ordered tubular structures (with ∼120 nm outside diameter). Both crystallization and doping processes were simultaneously accomplished in aqueous solution at a temperature as low as ∼90 °C, and the fastest doping process could be accomplished in 30 min for Fe doping. Besides, the surface areas of the doped TiO2 NTs were increased to 129.0 m2/g, and their absorption ranges could be expanded from 380 to >500 nm. This study shed light on a facile method for doping TM ions that is extendable to other semiconductors in the field of PEC water splitting and could improve their efficiencies as well.

Investigation of structural, optical, dielectric and magnetic properties of LaNiO3 and LaNi1−xMxO3 (M = Fe, Cr & Co; x = 5%) nanoparticles

This paper reports the synthesis of pure and doped lanthanum nickel oxide (LaNiO3) nanoparticles (NPs) using auto-combustion route. Various characterization techniques were employed for the investigation of the effect of transition metal doping on the structural, optical, magnetic and frequency dependent dielectric properties of this system. X-ray diffraction (XRD) results were used to calculate the crystallite size and phase composition of the nanoparticles. The well intense peaks in the XRD pattern confirmed the perfect doping of transition metal ions (Fe, Cr, Co) in the LaNiO3 lattice structure. The scanning electron microscopy (SEM) confirmed the porous surface morphology of the nanoparticles. The presence of various functional groups, stretching and vibrational modes were analyzed by the Fourier Transform Infra-Red (FTIR) technique. The energy band gap (Eg) of the synthesized materials were calculated from the absorbance spectra using Tauc’s relation. The band gap was observed to increase with doping indicating blue shift. The frequency dependent dielectric properties were measured at room temperature using LCR meter in the frequency range of 42 Hz to 5 MHz. It was observed that the dielectric constant and dielectric loss decreases with the increase in frequency. This decrease in dielectric constant as well as in dielectric loss with increase in frequency may be attributed to decreased polarization at higher frequency. The dielectric behaviour of LaNiO3 based perovskite oxides is explained on the basis of Koop’s theory which is based on Maxwell-Wagner two layer model. Vibrating sample magnetometer (VSM) was used to study the magnetic properties at room temperature and the obtained results confirmed the ferromagnetic nature of all the compositions.

Zn2+-improved upconversion luminescence of perovskite nanophosphors

CaTiO3 has received a great deal of attention as a promising functional material and a common fluorescent substrate, which could exhibit optical, piezoelectric, magnetic and catalytic performance. However, doping of transition metal ions in CaTiO3 has been rarely studied in the upconversion luminescent nanophosphors. Upconverting Zn2+-codoped CaTiO3:Yb3+, Er3+ nanostructures with improved red emission have been fabricated herein via a solvothermal reaction. The upconversion luminescence (UCL) properties are manipulated by means of the Zn2+ doping contents. The maximum integrated intensity ratio of red/green emissions (R/G) is observed at Zn2+ concentration of 13 mol%. Steady state and time resolved investigation suggested that Zn2+ ions codoping could release the crystal field symmetry around the activator ions, leading to the significant improvement of UCL efficiency as well as the R/G ratio. The results indicated that Zn2+-doped CaTiO3:Yb3+, Er3+ nanophosphors with tunable UCL properties could be employed as multifunctional nanocomposites in real application fields.