Controllable synthesis and luminescent properties of novel erythrocyte-like CaMoO4 hierarchical nanostructures via a simple surfactant-free hydrothermal route

Impact of luminescent-ion doping on the crystallographic and photo-physical properties of the CaMoO4 nanoparticles

Luminescent lanthanide (Ln3+ = Pr, Nd, Sm, Eu, and Tb)-ions doped calcium molybdate(CaMoO4) nanoparticles(NPs) were prepared by the polyol wet-chemical route. X-ray diffraction (XRD) pattern of all samples showed the formation of a single-phase scheelite type tetragonal structure with an average crystalline size over 21.6-33.4 nm. Thermal stability was evaluated to study the surface-anchored functional groups by weight loss measurement. Fourier transform infrared (FTIR) spectra were recorded to identify the adsorbed functional groups. Aqueous dispersibility and colloidal stability were recorded with the help of the UV/visible absorption spectra. These nanocrystals formed semi-transparent colloidal solutions after being evenly disseminated in aqueous media. The doping of the luminescent ions significantly affects the crystal structure and photoluminescence (PL) properties of the CaMoO4:Ln3+ NPs. In a comparative analysis of the absorption spectra, bandgap, Raman-active modes, and luminescent properties, they were greatly influenced by altering the dopant ion due to the variation in the atomic radius of the element. The doping of smaller atomic radius Ln3+-ions distorts the unit cell, and, subsequently, bond angle/length alters the symmetry of the host crystal. The distorted crystal lattice affects the crystalline, size, lattice parameter, band gap values, Raman active vibrational modes, and luminescent efficiency. The distorted crystal structure of the host lattices facilitates the movement of the oxygen vacancies through charge transfer, resulting in efficiently suppressed emission efficiency.Graphical abstract.

Structural and optical characterization of Er-doped CaMoO4 down-converting phosphors

xEr₂O₃-(1-x)CaMoO₄ (x = 1, 3, 5, 7 and 10 mol%) nanoparticles were synthesized by solid-state sintering at 800°C. X-ray diffraction studies confirmed the tetragonal crystal structure of CaMoO₄, while the doped samples show the co-existence of cubic Er₂O₃ and tetragonal CaMoO₄ and rule out the replacement of Ca²⁺ by Er³⁺ in the structure. The crystal unit-cell dimensions, phase concentration and atomic position coordinates were determined by Rietveld refinement. The short-range structure of CaMoO₄ consists of tetrahedral MoO₄ and snub disphenoid deltahedral CaO₈ units, while the unit cell of Er₂O₃ consists of two types of ErO₆ octahedral units. All MoO₄ units contain Mo-O bonds of equal lengths, whereas two types of slightly different Ca-O bond lengths exist in CaO₈. Raman spectra of the doped samples show only Mo-O vibrational modes and the Raman peaks of Er₂O₃ are masked by Mo-O bond vibrations. CaMoO₄ shows bluish-green emission at 500 nm, while Er-doped samples show strong green emission under UV excitation. UV irradiation (380 nm) induces down-conversion green emission at 531 nm and 552 nm and good color purity in 1 mol% Er₂O₃-CaMoO₄ sample which makes it a potential candidate for applications in optical devices.

Gold Nanoparticles Supported on Urchin-Like CuO: Synthesis, Characterization, and Their Catalytic Performance for CO Oxidation

Gold catalysts have been studied in-depth due to their unique activities for catalytic CO oxidation. Supports have intrinsic motivation for the high activity of gold catalysts. Thermally stable urchin-like CuO microspheres, which are potential support for gold catalysts, were prepared by facile solution-method. Then gold nanoparticles were loaded on them by deposition-precipitation method. The obtained gold catalysts were characterized by SEM, XRD, TEM, BET, ICP, and XPS. Their catalytic activity for CO oxidation was also evaluated. TEM results revealed that the gold nanoparticles with small sizes were highly distributed on the CuO surface in Au_1.0/CuO-300. XPS observations demonstrated that the gold species in Au_1.0/CuO-300 was of metallic state. Among the as-prepared catalysts, the Au_1.0/CuO-300 catalyst displayed the best performance for CO oxidation and achieved 100% CO oxidation at 80 °C. It kept 100% conversion for 20 h at a reaction temperature of 180 °C, and showed good reusability after three reaction-cycles. The possible catalytic mechanism of Au_1.0/CuO-300 catalyst for CO oxidation was also briefly proposed.

Enhancing the upconversion luminescence properties of Er3+–Yb3+ doped yttrium molybdate through Mg2+ incorporation: effect of laser excitation power on temperature sensing and heat generation

Upconversion luminescence was enhanced by incorporating Mg²⁺ into Er³⁺–Yb³⁺-doped yttrium molybdate and the effect of laser excitation power on temperature sensing and nanoheating was investigated.

Red and green colors emitting spherical-shaped calcium molybdate nanophosphors for enhanced latent fingerprint detection

We report the synthesis of spherical-shaped rare-earth (Eu³⁺ and Tb³⁺) ions doped CaMoO₄ nanoparticles in double solvents (IPA and H₂O) with the help of autoclave. The X-ray diffraction patterns well match with the standard values and confirm the crystallization in a tetragonal phase with an I4₁/a (88) space group. The luminescence spectra exhibit the strong red and green emissions from Eu³⁺ and Tb³⁺ ions doped samples, respectively. The X-ray photoelectron spectroscopy results show the oxidation states of all the elements present in the sample. The temperature-dependent luminescence spectra reveal the stability of Eu³⁺ and Tb³⁺ ions doped samples. The red- and green-emitting Eu³⁺ and Tb³⁺ ions doped CaMoO₄ samples were used for detection and enhancement of latent fingerprints which are the common evidences found at crime scenes. The enhanced latent fingerprints obtained on different surfaces have high contrast with low background interference. The minute details of the fingerprint which are useful for individualization are clearly observed with the help of these nanopowders.

Optically active multi-helical erythrocyte-like Ln(OH)CO3 (Ln = La, Ce, Pr and Sm)

Hierarchical erythrocyte-like Ln(OH)CO₃ with nanosized chiral structure-induced circular dichroism responses, assigned to valence to conduction band transitions and coupling effects between the left-handed-assembled Ln(OH)CO₃ nanorods in the multi-helical RBC-like architecture.

Controllable synthesis of uniform CaMoO4:Eu3+,M+ (M = Li, Na, K) microspheres and optimum luminescence properties

High-quality and monodisperse CaMoO₄:Eu³⁺,M⁺ (M = Li, Na, K) microspheres have been synthesized with the assistance of poly-(diallyldimethylammonium chloride) (PDDA) via a facile coprecipitation hydrothermal route.

A thin empty-shell bismuth tungstate hierarchical structure constructed by the acid sculpture effect with improved visible-light photocatalytic activity

A thin empty-shell Bi₂WO₆hierarchical structure is constructed using a simple acid sculpture strategy, which shows excellent photocatalytic activity.

Fabrication of coupled twin-shaped hollow hemispherical calcium molybdate via a facile ultrasound-assisted approach

Coupled twin-shaped hollow hemispherical calcium molybdate (CTHH-CaMoO₄) microstructures were successfully synthesized via a facile ultrasound-assisted template-free route in the presence of absolute ethanol and ethylenediaminetetraacetic acid (EDTA).