Layered Rare-earth Hydroxide Research Articles

Facile synthesis of nanoflowers of immobilized enzyme using layered rare earth hydroxides as carriers and their application for detection of H2O2 and phenol

This study reports a simple method for synthesizing the nanoflower-immobilized enzyme (LYH-HRP) using horseradish peroxidase (HRP) as the bioenzyme and layered yttrium hydroxide (LYH) as the inorganic carrier. Utilizing the structural advantage of LYH and the catalytic properties of HRP, a nanoflower-based colorimetric platform was newly designed and applied for sensitively detecting H2O2 and phenol with a detection time of as fast as 5 min. The limits of detection (LODs) for H2O2 and phenol are as low as 0.046 μM and 0.778 μM, respectively. The activity and stability tests showed that the activity of LYH-HRP was 1.52 times that of free HRP, and it maintained 75% of the initial activity after 60 days.

Dual-emission rare-earth fluorescent nanomaterials for ratiometric and visual detection of N-acetylneuraminic acid and applications in information encryption and anti-counterfeiting

N-acetylneuraminic acid (NANA) can be used as a biomarker for many types of cancers. Currently, there are various methods for detecting NANA but showing some shortcomings that limit the real-time diagnosis of cancer. In contrast, fluorescence analysis has obvious advantages such as low cost, fast response time, and easy operation, and it also enables visual detection for real-time cancer monitoring. Therefore, the establishment of an efficient and rapid detection method is essential for the early prevention and treatment of the disease. Based on the properties of layered rare-earth hydroxide (LRH), we synthesized a dual-emission fluorescent material (NDC/SDS-LEuH), and further fabricated a fluorescent nanoprobe (ANP) for the detection of NANA. The probe has the advantages of high sensitivity (LOD = 32.9 μM) and high selectivity with fast response. During the sensing process, the dual emission of the probe shows opposite changes due to the photoinduced electron transfer (PET) effect and the interaction between NANA and the probe. The color changes of the system can be observed under UV irradiation. Therefore, a visual platform was developed to detect NANA with a LOD of 0.09 mM. In addition, a probe hydrogel was prepared, which can be applied in the anti-counterfeiting to improve the difficulty of counterfeiting and the security of anti-counterfeiting. The probe achieves ratiometric fluorescence detection of NANA, which reduces background interference and improves the accuracy of detection. A visual detection platform was fabricated to realize the real-time detection. In addition, the prepared probe hydrogel showed the potential applications in anti-counterfeiting, which provided new ideas for the design and application of anti-counterfeiting materials.

Mg-modified layered erbium hydroxides promoting glucose transformation to lactic acid

Layered rare earth hydroxides (LREHs) with unique layer structure and tunable properties have shown attractive potentials as heterogeneous catalyst, but is still challenging in biomass valorization towards valuable chemical production due to the poor catalytic activity. Herein, Mg-modified erbium hydroxides (Mg-LErHs) with well-constructed layered structure have been first fabricated, where the properties and structure of Mg-LErHs significantly depend on the proportion of Mg. The results of catalyst characterizations reveal that Mg introduction increases the interlayer spacing and the content of Er(III)-O. Mg modification also hinders the desorption of crystallized H2O and dehydroxylation, thereby increasing the degree of crystallinity and promoting the stability of the catalyst. The activity test indicate that Mg modification greatly promotes the production of lactic acid from monosaccharides, where Mg(5.8)-LErHs affords the highest lactic acid yield of 60.9 %. Mg-LErHs also outperform other Mg-LREHs catalysts for the production of lactic acid. The highest catalytic activity of Mg(5.8)-LErHs are possibly attributed to its highest degree of crystallinity, and the increased layer spacing after Mg modification might have an advantage in facilitating the entry of substrate. The increased Er(III)-O content with high Lewis acidity might facilitate the combination with electronic-rich carbonyl oxygen in substrate. This research may provide a novel strategy to design the layered rare earth catalysts with tunable catalytic activity for biomass valorization.

Dual excitation channel ratiometric fluorescent probes for visual and fluorescent detection of anthrax spore biomarker and tetracycline hydrochloride

Long-term and excessive use of tetracycline hydrochloride (TC) can lead to its accumulation in the environment, which can cause water contamination, bacterial resistance, and food safety problems. 2,6-Pyridine dicarboxylic acid (DPA) is a major biomarker of Bacillus anthracis spores, and its rapid and sensitive detection is of great significance for disease prevention and counter-terrorism. A bifunctional ratiometric fluorescent nanoprobe has been fabricated to detect DPA and TC. 3,5-dicarboxyphenylboronic acid (BOP) was intercalated into layered europium hydroxide (LEuH) by the ion-exchange method and exfoliated into nanosheets as a fluorescent nanoprobe (PNP). DPA and TC could significantly enhance the red fluorescence of Eu3+ through the antenna effect under different excitation wavelengths, while the fluorescence of BOP can be used as a reference based on the constant emission intensity, realizing ratiometric detection. A low limit of detection (LOD) for the target (DPA: 9.7 nM, TC: 21.9 nM) can be achieved. In addition, visual detection of DPA and TC was realized using color recognition software based on the obvious color changes. This is the first ratiometric fluorescent nanoprobe based on layered rare-earth hydroxide (LRH) for the detection of DPA and TC simultaneously, which opens new ideas in the design of multifunctional probes.

Utilizing excited-state proton transfer fluorescence quenching mechanism, layered rare earth hydroxides enable ultra-sensitive detection of nitroaromatic

Convenient, rapid, and accurate detection of nitroaromatic organic toxins and harmful substances is of great significance in research. In the present study, two-dimensional layered rare-earth hydroxides (LYH) were used as ion-exchange matrix materials, and the anionic fluorescent dye molecules (HPTS) were successfully introduced into the LYH structures in situ via a simple and effective “plug-and-play” strategy, which gave the compounds ultra-sensitive fluorescence sensing detection of nitrobenzene, p-nitrotoluene and p-nitrophenol (Fluorescence response time < 1 sec, and the LOD for nitrobenzene, p-nitrophenol and p-nitrotoluene reached an impressive 349 ppb, 22 ppb and 98 ppb, respectively). Combined with theoretical calculations, we elucidated in detail the fluorescence quenching response mechanism of the LYH-HPTS towards nitroaromatic. Additionally, we also constructed fluorescent paper sensor, which effectively transformed the LYH-HPTS from theoretical detection to device application. The LYH-HPTS material is not only simple to synthesize, cost-effective and stable, but also has the features of fast response, excellent sensitivity and selectivity, and good reproducibility, which provides a new approach for the rapid and accurate detection of nitroaromatic.

A comprehensive solid-state NMR and theoretical modeling study to reveal the structural evolution of layered yttrium hydroxide upon calcination

Layered rare earth hydroxides (LREHs) are a new family of ion-exchangeable layered metal hydroxides, which have extensive applications in various fields due to the unique properties of rare earth cations in the layered structure and the anion exchange capacity. The transformation of layered metal hydroxides to new layered phases that can be restored through the memory effect is critical for their chemistry and applications. However, the structure details of these new phases such as the coordination environments of rare earth cations/counterions and their evolution as a function of calcination temperature remain unclear to date. Herein, a comprehensive 89Y/35Cl solid-state NMR (ssNMR) and theoretical modeling approach was used to reveal the structural evolution of a representative LREH, namely LYH-Cl, upon calcination. We first identified partial decomposition products of Y3O(OH)5Cl2 and Y(OH)3 during the dehydration stage, then uncovered the preferential removal of hydroxide ions on yttrium sites coordinated with chlorine during the dehydroxylation stage, and finally determined the preferential removal of chlorine exposed to the surface of layers during the dechlorination stage. The coordination environments of Y3+ and Cl− undergo significant changes upon calcination, revealed by ssNMR experiments. These findings thus help us to overcome the obstacles impeding the rational design and synthesis of LREH-based functional materials via memory effect, underscoring the vast potential of ssNMR in deepening the understanding of layered metal hydroxides and related materials.

Imparting Stable and Ultrahigh Proton Conductivity to a Layered Rare Earth Hydroxide via Ion Exchange.

Proton conductors are essential functional materials with a wide variety of potential applications in energy storage and conversion. In order to address the issues of low proton conductivity and poor stability in conventional proton conductors, a simple and valid ion-exchange method was proposed in this study for the introduction of stable and ultrahigh proton conductivity in layered rare earth hydroxides (LRHs). Test analyses by solid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, and powder X-ray diffraction revealed that the exchange of H2PO4- not only does not disrupt the layered structure of LRHs, but also creates more active proton sites and channels necessary for proton transport, thereby creating a high-performance proton conductor (LRH-H2PO4-). By utilizing this ion-exchange method, the proton conductivity of LRHs can be significantly enhanced from a low level to an ultrahigh level (>10-2 S·cm-1), while maintaining excellent long-term stability. Moreover, through methodically manipulating the guest ions and molecules housed within the interlayers of LRHs, a comprehensive explanation has been presented regarding the proficient mechanism of proton conduction in LRH-H2PO4-. As a result, this investigation presents a feasible and available approach for advancing proton conductor.

Layered rare-earth hydroxides as multi-modal medical imaging probes: particle size optimisation and compositional exploration.

Recently, layered rare-earth hydroxides (LRHs) have received growing attention in the field of theranostics. We have previously reported the hydrothermal synthesis of layered terbium hydroxide (LTbH), which exhibited high biocompatibility, reversible uptake of a range of model drugs, and release-sensitive phosphorescence. Despite these favourable properties, LTbH particles produced by the reported method suffered from poor size-uniformity (670 ± 564 nm), and are thus not suitable for therapeutic applications. To ameliorate this issue, we first derive an optimised hydrothermal synthesis method to generate LTbH particles with a high degree of homogeneity and reproducibility, within a size range appropriate for in vivo applications (152 ± 59 nm, n = 6). Subsequently, we apply this optimised method to synthesise a selected range of LRH materials (R = Pr, Nd, Gd, Dy, Er, Yb), four of which produced particles with an average size under 200 nm (Pr, Nd, Gd, and Dy) without the need for further optimisation. Finally, we incorporate Gd and Tb into LRHs in varying molar ratios (1 : 3, 1 : 1, and 3 : 1) and assess the combined magnetic relaxivity and phosphorescence properties of the resultant LRH materials. The lead formulation, LGd1.41Tb0.59H, was demonstrated to significantly shorten the T2 relaxation time of water (r2 = 52.06 mM-1 s-1), in addition to exhibiting a strong phosphorescence signal (over twice that of the other LRH formulations, including previously reported LTbH), therefore holding great promise as a potential multi-modal medical imaging probe.

Two-dimensional nanomaterials based on rare earth elements for biomedical applications.

As a kind of star materials, two-dimensional (2D) nanomaterials have attracted tremendous attention for their unique structures, excellent performance and wide applications. In recent years, layered rare earth-based or doped nanomaterials have become a new important member of the 2D nanomaterial family and have attracted significant interest, especially layered rare earth hydroxides (LREHs) and layered rare earth-doped perovskites with anion-exchangeability and exfoliative properties. In this review, we systematically summarize the synthesis, exfoliation, fabrication and biomedical applications of 2D rare earth nanomaterials. Upon exfoliation, the LREHs and layered rare earth-doped perovskites can be dimensionally reduced to ultrathin nanosheets which feature high anisotropy and flexibility. Subsequent fabrication, especially superlattice assembly, enables rare earth nanomaterials with diverse compositions and structures, which further optimizes or even creates new properties and thus expands the application fields. The latest progress in biomedical applications of the 2D rare earth-based or doped nanomaterials and composites is also reviewed in detail, especially drug delivery and magnetic resonance imaging (MRI). Moreover, at the end of this review, we provide an outlook on the opportunities and challenges of the 2D rare earth-based or doped nanomaterials. We believe this review will promote increasing interest in 2D rare earth materials and provide more insight into the artificial design of other nanomaterials based on rare earth elements for functional applications.

Cinnamate-Intercalated Layered Yttrium Hydroxide: UV Light-Responsive Switchable Material.

In recent years, there has been an increasing interest in stimuli-responsive host-guest materials due to the high potential for their application in switchable devices. Light is the most convenient stimulus for operating these materials; a light-responsive guest affects the host structure and the functional characteristics of the entire material. UV-transparent layered rare earth hydroxides intercalated with UV-switchable anions are promising candidates as stimuli-responsive host-guest materials. The interlayer distance in the layered rare earth hydroxides depends on the size of the intercalated anions, which could be changed in situ, e.g., via anion isomerisation. Nevertheless, for layered rare earth hydroxides, the possibility of such changes has not been reported yet. A good candidate anion that is capable of intercalating into the interlayer space is the cinnamate anion, which undergoes UV-assisted irreversible trans-cis isomerisation. In this work, both trans- and cis-cinnamate anions were intercalated in layered yttrium hydroxide (LYH). Upon UV-irradiation, the interlayer distance of trans-cinnamate-intercalated layered yttrium hydroxide suspended in isopropanol changed from 21.9 to 20.6 Å. For the first time, the results obtained demonstrate the possibility of using layered rare earth hydroxides as stimuli-responsive materials.

Crystallization of RE2(OH)2CO3SO4·nH2O as a new family of layered hydroxides (RE = Gd−Lu lanthanides and Y), derivation of RE2O2SO4, photoluminescence and optical thermometry

Layered rare-earth hydroxides (LREHs) draw wide research interest because of their peculiar crystal structure, rich interlayer chemistry and abundant functionality of the RE element, but are limited to the two categories of RE2(OH)5A·nH2O (A: typical of Cl− or NO3−) and RE2(OH)4SO4·nH2O. On the other hand, rare-earth oxysulfates (RE2O2SO4) have attracted attention due to their properties of large-capacity oxygen storage, low-temperature magnetism and luminescence, but their preparation procedure mostly involves toxic SOx gases and/or complicated procedures. In this work, RE2(OH)2CO3SO4·nH2O as a new family of LREHs (RE = Gd‒Lu lanthanides and Y) were produced via hydrothermal reaction, from which phase-pure RE2O2SO4 was derived via subsequent annealing at 800 °C in air without the involvement of SOx. The compounds were thoroughly characterized to reveal the intrinsic influence of lanthanide contraction (RE3+ radius) on crystal structure, thermal behavior (dehydroxylation/decarbonation/desulfurization), vibrational property and crystallite morphology. Through analyzing the photoluminescence of Eu3+ and Sm3+ in the Gd2O2SO4 typical host it is found that the 617 nm (Eu3+, λex = 275 nm) and 608 nm (Sm3+, λex = 407 nm) main emissions can retain as high as ∼79.6% and 85.5% of their room-temperature intensities at 423 K, with activation energies of ∼0.19 and 0.21 eV for thermal quenching, respectively. Application also indicates that both the phosphors have the potential for optical temperature sensing via the fluorescence intensity ratio (FIR) technology, whose maximum relative sensitivity reaches ∼2.70%/K for Eu3+ and 1.73%/K for Sm3+ at 298 K.

Multiple interactions steered high affinity toward PFAS on ultrathin layered rare-earth hydroxide nanosheets: Remediation performance and molecular-level insights

The global occurrence of per- and polyfluoroalkyl substances (PFAS) in aquatic systems has raised concerns about their adverse effects on ecosystems and human health. Adsorption is a promising technique for the remediation of PFAS, yet effective adsorbents with rapid uptake kinetics and high adsorption capacity are still in high demand, and molecular-level understanding of the interfacial adsorption mechanisms is lacking. In this study, we developed a superior layered rare-earth hydroxide (LRH) adsorbent, ultrathin Y2(OH)4.86Cl1.44·1·07H2O (namely YOHCl) nanosheets, to achieve the effective removal of perfluorooctanoic acid (PFOA). YOHCl nanosheets exhibited ultra-high adsorption capacity toward PFOA (up to 957.1 mg/g), which is 1.9 times and 9.3 times higher than the state-of-the-art layered double hydroxides (MgAl-LDH) and benchmark granular activated carbon (GAC) under the same conditions, respectively. Furthermore, YOHCl nanosheets pose stable performance on the removal of PFOA under various water matrices with robust reusability. We also developed YOHCl-based continuous-flow column, demonstrating its promise in simultaneously removing multiple PFAS with wide range of chain lengths at environmentally relevant concentrations. With the molecular-level investigations, we have revealed that multi-mechanism, including ion exchange, electrostatic attraction and bidentate/bridging coordination, contributed to the strong PFOA-YOHCl affinity, leading to the ultra-high adsorption capacity of PFOA. We have provided emerging LRHs-based adsorbents for the effective remediation of PFAS with molecular-level insights on the interfacial mechanisms.

Layered Gadolinium-Europium-Terbium Hydroxides Sensitised with 4-Sulfobenzoate as All Solid-State Luminescent Thermometers

Ternary layered gadolinium-europium-terbium basic chlorides were synthesised using a facile hydrothermal-microwave technique. A continuous series of solid solutions was obtained in a full range of rare earth concentrations. To sensitise the luminescence of Eu3+ and Tb3+, a 4-sulfobenzoate anion was intercalated in the ternary layered rare earth hydroxides using one of two methods—a high-temperature ion exchange or a single-stage synthesis. The luminescent colour of the materials was governed by the gadolinium content: at low and medium gadolinium concentrations (0–70%), layered Gd-Eu-Tb basic sulfobenzoate exhibited a bright red europium luminescence; at high gadolinium content (70–90%), a bright green terbium luminescence was observed. The colour coordinates of layered Gd-Eu-Tb basic sulfobenzoate luminescence depended on the temperature in the physiological range (20–50 °C). The relative thermal sensitivity of the obtained materials was up to 2.9%·K−1.

Pressureless sintering of LRH nanoplates on amorphous alumina for near‐infrared GAP:Mn4+ transparent ceramic film

AbstractTransparent ceramics have become a research hotspot in the preparation of fluorescent materials in recent years, because of their excellent physical and chemical properties and high transparency. Gadolinium aluminate, as a stable matrix material, is often doped with various active ions to obtain luminescence with different colors. However, it is very difficult to fabricate gadolinium aluminate transparent ceramics by a traditional method, although they are the charming solid lighting materials. Here, we developed a pressureless sintering method to prepare GdAlO3:Mn (GAP:Mn) transparent ceramic films, which were prepared by spin coating layered rare‐earth hydroxide (LRH) on amorphous alumina substrate and sintering at 1550°C for 2 h. Through the interface reaction, the Al2O3 reacted with Gd2O3 to form mesophase Gd4Al2O9 below 1550°C. However, the final products are GdAlO3 at 1550°C. The GAP:Mn4+ film exhibits a high transmittance of about 90%. Under UV excitation at 310 nm, the ceramic film outputs deep red and NIR emissions, which are both arising from the 2Eg–4A2g transition of Mn4+. Due to the electron traps arising from unequal valence substitution, the ceramic film exhibits a negative thermal quenching phenomenon. The ceramic film has a good luminescence thermal stability, because its emission intensity at 150°C maintains over 72% that at room temperature. This work may pave a new way to fabricate transparent ceramics using LRHs.

High-Entropy Layered Rare Earth Hydroxides.

New high-entropy layered rare earth hydroxides ─ (Y,Eu,Gd,Er,Sm)2(OH)5NO3, (Y,Eu,Gd,Er,Tb)2(OH)5NO3, (Y,Eu,Gd,Er,Yb)2(OH)5NO3, (Y,Eu,Gd,Er,Nd)2(OH)5NO3, and (Y,Eu,Gd,Er,Nd,Sm,Tb)2(OH)5NO3 ─ were obtained using a hydrothermal microwave method. The annealing of layered rare earth hydroxides at 900 °C resulted in the corresponding high-entropy rare earth oxides. Based on inductively coupled plasma atomic emission spectroscopy data, the values for configurational entropy for both rare earth hydroxides and oxides were estimated, confirming the formation of high-entropy compounds. Energy-dispersive X-ray spectroscopy mapping, including mapping in the scanning transmission microscopy mode, showed no signs of chemical segregation and confirmed uniform rare earth elements' distribution both in the particles of high-entropy layered basic nitrates and in the particles of high-entropy oxides. The ratios of rare earth cations in the initial aqueous solutions of mixed nitrates were close to the ratios of cations in the resulting high-entropy layered rare earth basic nitrates and high-entropy rare earth oxides.

A tripartite-enzyme via curcumin regarded as zymoexciter towards highly efficient relieving reperfusion injury

For alleviating ischemic reperfusion injury, reasonable design mimic multi-functional nanozyme can simultaneously capture ROS and inhibit inflammatory factors, which plays an important role. However, the low efficiency of natural enzyme and their ability to capture only a single species limit their effectiveness. Therefore, additional materials to capture other ROS are highly needed. These motivates us to construct a nanozyme via hybridize/coupled curcumin (CUR) with ZnCe Layered Rare-earth Hydroxide (ZnCe-LRH) to achieve highly efficient ROS scavenging efficiency and the multiple ROS capture (denoted as CUR/ZnCe-LRH). Ce element was highly dispersed on the LRH layer, and CUR further coordinated with Zn on the layer to form a stable nanozyme structure. This mimic tripartite nanozyme can not only simulate superoxide dismutase (SOD) and catalase (CAT) activity to capture •O2− and H2O2, but also arrest •OH within a short period of time, which can be regarded as the tripartite nanozyme. Density functional theory (DFT) calculations can further confirm the high efficient ROS scavenging mechanism by the CUR/ZnCe-LRH systems. In vivo results can further probe that this CUR/ZnCe-LRH can also suppress inflammation- and immune response–induced injury, thus achieving good prevention and treatment in neuroprotective therapy. The infarct area can reduce by 78% after the reperfusion therapy and the neurological deficit score can reduce from 3.50 to 0.67. This strategy provided a novel multifunctional enzyme mimetic for ischemia–reperfusion therapy and clarifies the application mechanism of neuroprotection against ischemia–reperfusion injury.

Exploring the intercalation chemistry of layered yttrium hydroxides by 13C solid-state NMR spectroscopy

Layered rare earth hydroxides (LREHs) are a novel class of two-dimensional materials with potential applications in various fields. The exchange reactions with organic anions are typically the first step for the functionalization of LREHs. Although the laminar structures seem to be clear for anion-exchanged compounds, the state of intercalated organic anions and their interactions with cationic rare earth hydroxide layers remain unclear. Herein, we demonstrate that the use of 13C solid-state nuclear magnetic resonance (ssNMR) spectroscopy enables to extract key information on the state of intercalated organic anions such as their local chemical environment, stacking, and dynamics, which are often difficult or impossible to obtain previously. In combination with powder X-ray diffraction and ab initio density functional theory calculations, the intercalation chemistry of two representative layered yttrium hydroxides with selected monovalent organic anions was studied in detail. The products can undergo secondary exchange with a divalent organic anion, depending on the match between the basal spacing of two phases, i.e., the replacement of benzenesulfonate (BS−), 2,4-dimethylbenzene sulfonate (DMBS−), and 4-ethylbenzene sulfonate (EBS−) with 2,6-naphthalene disulfonate (NDS2−) is allowed due to the insignificant change in basal spacing after exchange, while the replacement of very long dodecyl benzene sulfonate (DBS−) and dodecyl sulfate (DS−) with NDS2− is forbidden. The results therefore provide valuable insights into the structure-property relationships of LREH-based functional materials.

Rare-Earth hydroxide nanosheets based ratio fluorescence nanoprobe for dipicolinic acid detection

We demonstrate a novel ratio fluorescence nanoprobe for dipicolinic acid (DPA) as an anthrax biomarker based on layered rare-earth hydroxide (LRH). 3-Amino-benzenesulfonic acid (AS) was intercalated into layered terbium hydroxide to form composite and then delaminated into nanosheets in formamide. The monolayer nanosheets were beneficial to expose the Ln3+ luminescence centers to the environment more completely, contributing a high sensitive detection to the environment. With the increase of DPA concentration, the emission intensity of AS kept constant which worked as a stable internal reference, while the fluorescence of Tb3+ was enhanced obviously due to the antenna effect. In the 0.05–5.0 μM concentration range, the I544/I360 fluorescence ratio changed with the DPA concentration, which exhibited a good linear relationship (R2 = 0.999) and an ultralow detection limit of 3.8 nM. In addition, the probe showed high selectivity and sensitivity to the DPA detection as an anthrax biomarker, which can be applied in real tap water with good performances. This work could extend the applications of LRH nanosheets in detection and offer an extremely effective and easy technique for detecting DPA.

Low-temperature synthesis of NaRE(WO4)2 films via anion exchange from layered rare-earth hydroxides (LRHs) films, phase/morphology evolution and photoluminescence

LRH films were prepared via electrodeposition within 10 minutes, and they were used as precursor templates to produce NaRE(WO4)2 films at pH ∼ 10. The obtained NaEu(WO4)2 and NaTb(WO4)2 films exhibit enhanced photoluminescence.

Fabrication of REVO4 films via sacrificial conversion from layered rare-earth hydroxide (LRH) films: the investigation of the transition mechanism and their photoluminescence.

Rare-earth orthovanadate REVO4 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Y) films were directly synthesized within 2 hours by sacrificial conversion from electrodeposited layered rare-earth hydroxide (RE2(OH)5NO3·nH2O) films at pH ∼ 10, without subsequent heat treatment. Detailed characterization of the products was achieved by combined X-ray diffraction, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence excitation and photoluminescence. The mechanisms of phase and morphology evolution from Y2(OH)5NO3·nH2O to YVO4 were unveiled through systematic investigations into the influences of the concentration of the anion sources (Na3VO4) and the reaction temperature. The effects of lanthanide contraction on the phase structure and particle morphology of the REVO4 films were also clarified. Additionally, the photoluminescence of RE3+ activators (RE = Eu, Dy, and Eu and Dy) was elaborated with YVO4 as a representative host lattice, and the color-tunable emission and energy transfer from Dy3+ to Eu3+ were also investigated. Electrodeposition combined with a hydrothermal anion exchange technique established in this study led to the rapid synthesis of REVO4 films, and it might have wide implications for the generation of other types of inorganic functional films.