Rare Earth Hydroxides Research Articles

Assemblies of organic/inorganic colloids and composite films with controlled luminescence through layered Lu-(Eu,Tb,Ce) hydroxides

As a kind of two-dimensional multifunctional material, the optical studies of layered rare-earth hydroxides are receiving growing attention. Herein, the layered lutetium hydroxides (LLuHs) bound with NO3– were fabricated through a hydrothermal process, in which Tb3+, Eu3+ and Ce3+ ions were doped as green, red and blue emission centers, respectively. To improve the luminescence and photofunctional performances of LLuHs, a series of organic benzoic anions were intercalated into LLuHs by ion-exchange reactions. The results indicated that the LLuHs possessed typical lamellar structure and appearance. The luminescence intensities of LLuH:Tb and LLuH:Eu were significantly enhanced through selecting appropriate benzoic anions. Assisted with supporting agent, the LLuH:Tb and LLuH:Eu as well as LLuH:Ce assemblies were exfoliated to two-dimensional nanosheet colloids with bright characteristic emissions. The emitting color of colloids could be modulated by adjusting the volume ratio and excitation wavelength. Under a specific volume ratio, nearly white light emission was observed when irradiated with 254 and 365 nm ultraviolet light, simultaneously. Moreover, the luminescence-controlled transparent composite films were prepared by using the organic/inorganic assemblies, and could be folded and constructed with various shapes. This work expands the members of two-dimensional materials and promotes the photofunctional development of layered rare-earth hydroxides.

Research Progress and Application of Layered Rare Earth Hydroxides, a Class of Inorganic Layered Compounds with Photoluminescence.

Inorganic layered compounds are an important part of organic-inorganic functional nanocomposites and offer plentiful opportunities and possibilities for synthesizing new-style multifunctional materials because they could be intercalated, exfoliated, and swollen. In recent years, as inorganic layered materials with photoluminescence, layered rare earth hydroxides (LRHs) have been extensively studied. Due to their rich functionalization ways, they have been applied or shown potential application value in many fields such as pollution detection, biomedicine, photoelectric energy storage, and so on. On account of the basic physical and chemical properties, the basic structures of LRHs may be regulated through exfoliation and intercalation, which provides more possibilities for synthesizing new multifunctional composite materials and broadening and updating their application fields. In this paper, LRHs are extracted from inorganic layered compounds, and the structure, synthesis, research progress, and application of LRHs are summarized in detail, which lays a great theoretical foundation for further exploration and optimization of the application as a composite functional material in industry, medicine, detection, optoelectronics, and other fields.

The Ordering and Arrangement of Intercalated Carboxylate Ions in Anion‐Exchangeable Layered Yttrium Hydroxides

AbstractThe intercalation chemistry is essential in the application of anion‐exchangeable layered metal hydroxides. However, much of the key information regarding intercalated anions, such as the degree of ordering and arrangement is still not clear or missing to date, due to the difficulty in probing the local environment of anions by routine characterization techniques. Herein, we employed solid‐state NMR (ssNMR) spectroscopy to offer valuable complementary insights into the ordering and arrangement of a series of monocarboxylate anions (RCOO−: R=HO, H, CH3, C2H5, and C3H7) within the interlayer space of two layered yttrium hydroxides (LYH‐Cl and LYH‐Br). The results imply that the two smaller carboxylate anions (R=HO and H) are disordered after intercalation, while the larger carboxylate anions (R=CH3, C2H5, and C3H7) are relatively ordered. We further explored if the intercalated anions are parallel arranged as those in sodium salts or antiparallel arranged as those predicted in the majority of previous reports. We uncovered that the intercalated anions are antiparallel arranged based on the formation energy obtained in density functional theory calculations and ssNMR data. Our results therefore contribute to a deeper and comprehensive understanding of the intercalation chemistry of layered rare earth hydroxides.

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.

Layered Double Hydroxides as Next-Generation Adsorbents for the Removal of Selenium from Water

This research paper provides a comprehensive overview of the use of layered double hydroxides (LDH) in the removal of selenium species from contaminated water sources. Key studies on sorption mechanisms and the impact of competing ions on selenium removal are presented, and the effectiveness of LDH is compared across different structures and compositions. Scholarly sources extensively document the application of conventional LDH for effective selenium removal, with notable advancements achieved through innovative synthesis approaches. Comparative studies between LDH synthesized through various methods reveal the potential of tailored LDH for enhanced selenium adsorption. The paper further explores the influence of competing anions on LDH efficacy, emphasizing the impact of sulfate on selenium removal. Additionally, investigations into calcined LDH and commercially available variants underscore the potential for industrial applications. Beyond conventional LDH, the paper delves into iron-based LDH, LDH with intercalated thiomolybdate anions, and layered rare earth hydroxides, exploring their effectiveness in separating different selenium species. The role of pH in the removal of selenium species and the impact of three-metal cation LDH are also discussed. The study extends to nanocomposites, combining LDH with zero-valent iron, carbon-based materials, and organic compounds, illustrating their potential for selenium species immobilization. The presented findings offer valuable insights for researchers and practitioners in environmental science, addressing the growing demand for efficient selenium remediation strategies.

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.

The rare-earth elements recovered from the leachate of discarded phosphor by electrodeposition

ABSTRACT Recovering rare-earth elements (REEs) from discarded phosphors is an important solution to alleviate the current shortage of rare-earth resources, the aluminum element in discarded phosphors will badly affect the purity and recovery of rare-earth elements. An electrodeposition method for recovering the rare earth from the discarded phosphoric leachate was proposed to avoid the effecting of aluminum elements. The results show that the purity of the rare-earth oxides recovered reached 99.13% and the recovery rate of rare-earth elements reached 98.89% by adopting the optimal electrodeposition process with the help of the complexing agent glycine. Research has found that adding the complexing agent glycine can help rare-earth hydroxides precipitate at the cathode and inhibit aluminum ion precipitation by changing the aluminum deposition potential. Moreover, it was also found that the generation of OH- ions by reduction of NO3- in acid aqueous solution was a one-step irreversible reaction in the deposition process by cyclic voltammetry, which ensured the reliability of rare-earth hydroxide precipitation reaction.

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.

Recovery of rare earths from rare earth molten salt electrolytic slag using alkali phase reconstruction method with the aid of external electric field

Rare earth molten salt electrolytic slag (RMES) has emerged as a promising secondary resource for rare earth elements (REEs). This study introduces an innovative leaching technique for extracting REEs from RMES under atmospheric conditions, employing an alkali phase reconstruction method followed by an acid leaching process. Additionally, the external electric field was employed to enhance the reaction. Under the optimal reaction conditions: NaOH initial concentration of 70 wt%, NaOH-slag mass ratio of 4:1, temperature of 160 °C, current density of 1000 A/m2, reaction time of 90 min, stirring speed of 300 r/min, HCl concentration of 4 mol/L, liquid-solid ratio of 15:1, and leaching time of 20 min, the leaching efficiencies of Nd and Pr reach up to 99.21% and 99.14%, respectively. Phase analysis indicates that the rare earth fluorides transform into rare earth hydroxides, significantly enhancing their solubility in acid solution. The imposition of an external electric field leads to pronounced disruption of the RMES surface, thereby promoting the formation of stable reactive oxygen species in the alkaline medium. This facilitates the decomposition of fluorinated rare earths and hastens the phase reconstruction, resulting in an enhanced leaching process. The achieved leaching efficiency with an external electric field is 37% higher than that without an electric field.

Enhanced oxygen evolution reaction performance of nitrogen-doped carbon dots sensitized with rare-earth metal nanorods

An affordable, sustainable, effective, and strong catalyst for oxygen evolution reaction (OER) processes has gained increased significance because of its crucial role in energy conversion and storage. Heteroatom-doped amorphous carbon materials made from biomass have lately come into prominence as inexpensive, environmentally benign, renewable, and sustainable materials. Substantial research about the incredible performance in OER by carbon dots has been devoted, yet durability remains a challenge. Therefore, we reported novel carbon dots doped with a heteroatom (nCDs) included with Gd(OH)3, a rare-earth hydroxide element. Taking advantage of numerous active and edge sites of CDs and modifying the chemistry of the surface by doping with foreign atoms, the prepared nCDs/Gd(OH)3 revealed the outstanding catalytic performance of a low overpotential of 280 mV at a Tafel slope of 127 mV/dec at 10 mA/cm2 in sluggish alkaline medium. Our findings supported the synergistic interaction between the doped heteroatom and its surface's maximal exposure of nCDs/Gd(OH)3 sites, facilitating the rapid transport of reactants and sufficient contact to enhance OER performance. This study will garner more attention in the context of producing sustainable energy and storing it effectively. For clean, green energy, combining carbon dots with rare earth metals is an emerging candidate for energy conversion. The alkaline electrolyzer will find it to be a promising electrocatalyst, especially in seawater medium.

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.

Multistage hydrometallurgical process for enhanced recovery and individual separation of Nd and Pr from NdFeB magnet scrap

This study introduces a multistage hydrometallurgical process designed for the recovery and individual separation of Nd and Pr from NdFeB magnet scrap. Following demagnetization, the magnet underwent crushing, grinding, and leaching using a sulfuric acid solution. The pH of the resultant leachate was subsequently adjusted to 1.2 using a NaOH solution, leading to the precipitation of Nd and Pr as sodium double sulfates. The produced double sulfate was then mixed with a saturated NaOH solution, resulting in the formation of rare earth hydroxide. The hydroxide was further decomposed into oxides (REO) after calcination at 500°C. The REO was dissolved in hydrochloric acid and nitric acid solutions to investigate the individual separation of Nd and Pr using the D2EHPA–TOA extractant system and compare the results with D2EHPA-only system. It was concluded that the extraction mechanism of D2EHPA–TOA system is highly dependent on the acidity of the solution, with TOA having a synergistic effect on the REE extraction when pH &gt; 3, and an antagonistic effect when pH ≤ 3. In terms of extraction efficiency, both extractant systems demonstrated efficiency levels exceeding 99% when the pH was ≥2, with similar behavior when extraction was performed in HCl and HNO3 media. Although both extractant systems yielded unsatisfactory outcomes in the separation of Nd and Pr, a marginal improvement was observed with the incorporation of TOA into the extractant system. This observation implies the potential of exploring analogous combinations in future studies.

Selective pseudocapacitive immobilization of REE elements on carbon based electrodes

Current extraction technologies for rare earth elements at ambient conditions are reagent and energy intensive, giving rise to significant quantities of secondary waste streams. Exploration of the removal of common cations from aqueous streams has been undertaken with carbon materials and have shown promising results. However, those promising materials have not been explored extensively for rare earth element capture from aqueous process streams. In this study, a carbon electrode was investigated for the adsorption and immobilization of REE elements from aqueous solutions. Cyclic voltammetry studies of the carbon electrode displayed a pseudocapacitive behavior where it was verified that cation adsorption is accompanied by an electron transfer process. Preliminary tests showed that a current density of 89.1 mA. g−1, allowed for the pseudocapacitive adsorption (PSA) of Nd3+ cation without the formation of rare earth hydroxides. Hence, the selective PSA of Nd3+ was verified in an electrolyte solution with equimolar concentrations of Nd3+, Mg2+, Li+, Na+ and K+, achieving separation factors of 8.6, 1.1, and 10.9 for Nd3+/Li+, Nd3+/Na+, and Nd3+/Mg2+, respectively. Analysis of the potential-time curves for the various cations suggests that storage of ions in the electrode involved pore-spacings rather than interlayer spacings and was corroborated by XRD analysis. Specific capacitance as high as >640 F.g−1 for Nd3+ was also observed for the carbon electrode, with Faradaic efficiencies (FE) of >20 % for Nd3+ and Mg2+, and >9 % for Na+. Furthermore, adsorption capacity of >125 mg g−1 after 4hrs of electrosorption was observed for Nd3+. In the presence of the Nd3+ electrolyte, the electrode achieved increasing storage of Nd3+ with >94 % retention of Nd3+ with a FE > 20 % over 6 cycles between loading and releases in 1 M KCl solution. These preliminary results provide information and some guidance on the selective recovery of rare earth elements, such as Nd, in aqueous streams in the presence of competitive cations employing the use of carbon-based materials.

Reducing rare earth loss by adding acetic acid in the aluminum removal process of rare earth leaching solution

The ionic-type rare earth ore, abundant in medium and heavy rare earth elements, is a strategic mineral resource. The removal of aluminum from ionic rare earth leaching solution results in over 8% loss of rare earths. Preliminary research has found that adding acetic acid (HAc) during aluminum removal process can effectively reduce the loss of rare earth elements. In this paper, through the calculation of the species distribution in the La2(SO4)3-Al2(SO4)3-HAc-H2O system, it is found that HAc forms an AlOH-Ac+ complex with aluminum ions, with a proportion of up to 70%, which will increase the initial precipitation pH of aluminum hydroxide. Furthermore, HAc and lanthanum form a LaAc2+ complex, and the proportion can reach more than 20%. Moreover, the zeta potential, FT-IR, and XPS tests of aluminum hydroxide, obtained by neutralization precipitation, revealed that the complexation of HAc and aluminum can reduce the precipitation rate of aluminum hydroxide, so that its particle size increases, the specific surface area decreases, and the van der Waals force adsorption sites are reduced. HAc can be chemically adsorbed on aluminum hydroxide, thereby increasing the zeta potential of aluminum hydroxide and ultimately reducing its electrostatic adsorption effect on rare earths. Additionally, the complexation of HAc and rare earth elements can reduce the local supersaturation of rare earth hydroxides and decline the coprecipitation of rare earth elements. Finally, under a precipitation endpoint pH of 5.2, HAc concentration of 0.006 mol/L, aluminum concentration of 0.2 g/L, rare earth concentration of 0.8 g/L, magnesium ion concentration of 0.5 g/L and magnesium oxide slurry concentration of 0.45 mol/L, the aluminum removal efficiency obtained with rare earth leaching solution reached 98.47%, and the rare earth loss efficiency was 2.62%. Compared with the control, the rare earth loss efficiency was reduced by 5.59%. This paper provides guidance for the efficient and green development of ionic-type rare earth ore.

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.

Fast and versatile electrodeposition of vertically aligned layered rare-earth hydroxide nanosheets for multicolour luminescence and oil/water separation

LYH films were prepared via electrodeposition on ITO glass and metal mesh. Bases on the new synthesis, oil/water separators and Y2O3:RE films with multicolor luminescence were obtained.

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.