Phase-Dependent Enhancement of the Green-Emitting Upconversion Fluorescence in LaVO4:Yb3+, Er3+

Optimizing optical thermometry with tri-doped Ba2GdV3O11 phosphors: Ratiometric and fluorescence lifetime analysis

Optical sensor technology has undergone a transformative evolution with the advent of fluorescence ratio techniques (FIR) and fluorescence lifetime (FL) strategies, revolutionizing precision, performance, and reliability. This study delves into the synthesis of Ba2GdV3O11 phosphors doped with Ho3+/Nd3+, Er3+, and Yb3+, employing the sol-gel method for upconverting material fabrication. A thorough investigation into the structural, morphological, and optical properties of the synthesized phosphors is conducted. Excitation at 980 nm unveils upconversion (UC) emissions across green and red spectra. The intensities of the observed emission bands for Ho3+, Nd3+, and Er3+ demonstrate significant sensitivity to fluctuations in temperature. Temperature sensing relies on the 4S3/2 and 2H11/2 upconversion emissions bands, in addition to the emission lifetimes at 4S3/2. Enhanced thermal sensitivity values are attained, reaching up to 1.03 % K-1 and 1.07 % K-1 using the FIR strategy, and up to 0.146 % K-1 and 0.47 % K-1 with the FL strategy for Ho3+/Er3+/Yb3+ and Nd3+/Er3+/Yb3+ tri-doped Ba2GdV3O11 phosphors, respectively. Furthermore, the studied phosphors exhibit remarkable precision in detecting minute temperature changes (0.3 K), positioning them as promising candidates for precise temperature sensing. This study pioneers innovative methodologies to advance optical thermometry techniques, offering promising prospects for scientific and industrial applications reliant on precise optical temperature sensing.

Comparative studies of upconversion luminescence and optical temperature sensing in Tm3+/Yb3+ codoped LaVO4 and GdVO4 phosphors

Tm³⁺/Yb³⁺ codoped LaVO₄ and GdVO₄ phosphors are successfully synthesized using solid state reaction methods and then upconversion emission studies are performed. X-ray diffraction has confirmed a pure monoclinic phase of LaVO₄ and a tetragonal phase of GdVO₄. Upconversion emission through 980 nm laser diode excitation has shown a strong blue band at 475 nm and two weak red bands at 647 and 700 nm originating from ¹G₄ → ³H₆, ¹G₄ → ³F₄ and ³F₃ → ³H₆ transitions of Tm³⁺ ions, respectively. Non-thermally coupled levels viz.³F₃ (700 nm) and ¹G₄ (475 nm) in both the phosphors are used for fluorescence intensity ratio based optical thermometric studies and a comparison is made. The FIR data against temperature were fitted with polynomial and exponential fittings. The results show that polynomial fitting has a higher absolute sensitivity of 21.2 × 10^-3 K^-1 at 653 K for the LaVO₄: Tm³⁺/Yb³⁺ phosphor than the exponential fitting sensitivity of 19.0 × 10^-3 K^-1 at 653 K, while in the case of the GdVO₄: Tm³⁺/Yb³⁺ phosphor both fitting functions provided the same value of absolute sensitivity, that is 13.0 × 10^-3 K^-1 at 653 K. A comparison of the sensitivity values shows that the LaVO₄: Tm³⁺/Yb³⁺ phosphor provides higher sensitivity than the GdVO₄: Tm³⁺/Yb³⁺phosphor but the latter one is too high in upconversion emission.

Low-temperature synthesis, characterization and photocatalytic properties of lanthanum vanadate LaVO4

In this study, we have successfully prepared tetragonal lanthanum vanadate LaVO4 nanoparticles by a facile co-precipitation method at room temperature. The obtained materials were characterized using different structural and micro-structural techniques such as the characterization by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectrum (DRS), transmission electron microscopy (TEM), and Raman spectrometry. The obtained structure is crystallized in single tetragonal phase with pin-like nanostructure. A main optical transition with bandgap energy of 3.26 eV is evidenced, and the average lifetime of charges carriers was found to be 1 ns Furthermore, the photoluminescence occurs in the visible light range. The photocatalytic activity was evaluated by the photocatalytic degradation of methylene blue (MB) with initial concentration of 10 mg L-1. The result indicates that LaVO4 particles showed a best photocatalytic activity of 98.2% degradation for methylene blue solution after irradiation of 90 min under visible light. Furthermore, the photocatalytic mechanism and reusability were studied.

Optical temperature-sensing properties based on upconversion luminescence of La9.31Si6.24O26:Er3+,Yb3+ with different strategies

A series of novel La_9.31Si_6.24O₂₆:Er³⁺,Yb³⁺ (LS:Er³⁺,Yb³⁺) luminescent materials have been successfully synthesized by conventional solid-state reaction method. The phases, morphologies and upconversion (UC) luminescence properties were systematically researched by XRD, SEM, PL spectra, etc. The optimum Yb³⁺ concentration in LS:1%Er³⁺,xYb³⁺ was determined to be ×  = 15%, above which the concentration quenching effect appeared due to the increasing energy back transfer from Er³⁺ to Yb³⁺. Meanwhile, the FIR technique (by using I₅₂₂/I₅₅₄ and I₆₆₀/I₅₂₂ of Er³⁺) was employed to study the temperature-sensing performance. As the rise of temperature for all the different Yb³⁺ concentrations, the values of the absolute sensitivity S_A increased first and then decreased by utilizing I₅₂₂/I₅₅₄, but showed continuous decrease by using I₆₆₀/I₅₂₂. For the relative sensitivity S_R, it has been found that the S_R values for all the samples exhibited gradual decrease with rising temperature. Besides, the experiment of the heating-cooling cycles between 283 and 523 K proved that the LS:Er³⁺,Yb³⁺ material has good reversibility and repeatability. The above results indicated that the LS:Er³⁺,Yb³⁺ may be a potential candidate for optical temperature sensor.

Tailoring the Radionuclide Encapsulation and Surface Chemistry of La(223Ra)VO4 Nanoparticles for Targeted Alpha Therapy

The development of targeted alpha therapy (TAT) as a viable cancer treatment requires innovative solutions to challenges associated with radionuclide retention to enhance local tumor cytotoxicity and to minimize off-target effects. Nanoparticles (NPs) with high encapsulation and high retention of radionuclides have shown potential in overcoming these issues. This article shows the influence of pH on the structure of lanthanum vanadate (LaVO4) NPs and its impact on the radiochemical yield of 223Ra and subsequent retention of its decay daughters, 211Pb and 211Bi. An acidic pH (4.9) results in a high fraction of La(223Ra)VO4 NPs with tetragonal structure (44.6–66.1%) and a 223Ra radiochemical yield <40%. Adjusting the pH to 11 yields >80% of La(223Ra)VO4 NPs with monoclinic structure and increases the 223Ra radiochemical yield >85%. The leakage of decay daughters from La(223Ra)VO4 NPs (pH 11) was <5% and <0.5% when exposed to deionized water and phosphate-buffered saline, respectively. Altering the surface chemistry of La(223Ra)VO4 NPs with carboxylate and phosphate compounds resulted in a threefold decrease in hydrodynamic diameter and a 223Ra radiochemical yield between 74.7% and 99.6%. These results show the importance of tailoring the synthesis parameters and surface chemistry of LaVO4 NPs to obtain high encapsulation and retention of radionuclides.

Upconversion photoluminescence of Ho3+-Yb3+ doped barium titanate nanocrystallites: Optical tools for structural phase detection and temperature probing

Authors have explored the photo-physical properties of Ho³⁺-Yb³⁺ doped BaTiO₃ nanocrystals and proposed an intuitive method to probe temperature and crystal phase structure of the matrix. Structural phase change of doped crystals was analyzed in terms of their X-ray diffraction, and it was confirmed through second harmonic generation. We give insights on upconversion of energy of light-emission in Ho³⁺-Yb³⁺: BaTiO₃ nanocrystals upon a 980 nm laser-light excitation and subsequently, the excited state dynamics were studied with the help of dependence of upconversion luminescence on excitation power and measuring-temperature. To understand the nature of occupancies of the Ho³⁺ ions at the Ti- and Ba-sites, we performed site-selective, time-resolved spectroscopic measurements at various crystal phases. Based on the lifetime analysis, it is inferred that the Ho³⁺ ions are present at two types of sites in barium titanate lattice. One of those is the 6-coordinated Ti-site of low symmetry, while the other one is the 12-coordinated Ba-site of higher symmetry. The upconversion emission of the nanocrystals are found to be temperature-sensitive (12 to 300 K), indicating possible use as a self-referenced temperature probe. An analysis of the temperature dependent emissions from ⁵F₄ and ⁵S₂ levels of Ho³⁺ ions, gives a maximum value of temperature sensitivity ~ 0.0095 K⁻¹ at 12 K. Furthermore, we observe a sharp change in the luminescence intensity at ~180 K due to a ferroelectric phase change of the sample. The correlation of upconversion luminescence with the results of X-ray diffraction and second harmonic generation at different crystal phases implies that the frequency upconversion may be used as a probe of structural change of the lattice.

Temperature-sensing luminescent materials La9.67Si6O26.5:Yb3+–Er3+/Ho3+ based on pump-power-dependent upconversion luminescence

Rare earth ion doped upconversion (UC) luminescent materials could show potential applications in optical temperature sensing.

A Polyol-Mediated Fluoride Ions Slow-Releasing Strategy for the Phase-Controlled Synthesis of Photofunctional Mesocrystals

There are only a few inorganic compounds that have evoked as much interest as sodium yttrium fluoride (NaYF₄). Its extensive applications in various fields, including transparent displays, luminescence coding, data storage, as well as biological imaging, demand the precise tuning of the crystal phase. Controlling the emergence of the desired α-phase has so far remained a formidable challenge, especially via a simple procedure. Herein, we represented a polyol-assisted fluoride ions slow-release strategy for the rational control of pure cubic phase NaYF₄ mesocrystals. The combination of fluorine-containing ionic liquid as a fluoride source and the existence of a polyalcohol as the reactive medium ensure the formation of uniform α-phase mesocrystallines in spite of a higher temperature and/or higher doping level.

Morphology/phase controllable synthesis of monodisperse ScVO4 microcrystals and tunable multicolor luminescence properties in Sc(La)VO4(PO4):Bi3+,Ln3+ phosphors

A facile one-pot hydrothermal approach was employed to prepare novel chocolate-like ScVO₄ microcrystals using polyethylene glycol as an additive.

Facile Synthesis of Highly Water-Soluble Lanthanide-Doped t-LaVO4 NPs for Antifake Ink and Latent Fingermark Detection

In the information age, it is important to protect the security and integrity of the information. As a result, the fluorescent ink as an antifake technology and the fingermark as an information carrier have aroused great interest. In this work, highly water-soluble lanthanide (Ln³⁺ )-doped tetragonal phase (t-) LaVO₄ nanoparticles (NPs) are successfully obtained via a simple, fast, and green microwave-assisted hydrothermal method. The average size of t-LaVO₄ NPs is about 43 nm. The aqueous solutions of Ln³⁺ -doped t-LaVO₄ exhibit excellent fluorescence properties under ultraviolet light (UV) excitation (t-LaVO₄ :10%Eu is bright red and t-LaVO₄ :0.5%Dy is close to white). Some superb antifake fluorescent patterns are printed using Ln³⁺ -doped t-LaVO₄ aqueous solution as ink, which indicates the as-prepared Ln³⁺ -doped t-LaVO₄ NPs as fluorescent ink can meet the various antifake requirements. Notably, the designed convenient antifake fluorescent codes with improved security could be directly scanned and decoded by a smart phone. What's more, the as-prepared NPs can be used for the development of latent fingermark on various substrates and the second-level detail information can be clearly obtained from the magnification of a fingermark. These results indicate that the as-prepared Ln³⁺ -doped t-LaVO₄ fluorescent NPs have great potential in security application.

Enhanced anti-stocks luminescence in LaNbO4:Ln3+ (Ln3+ = Yb3+, Er3+/Ho3+/Tm3+) with abundant color

A 980 nm laser was employed to excite Yb³⁺ ions to achieve the 2F_7/2 → 2F_5/2 transition, and the LNO:Yb³⁺, Er³⁺/Ho³⁺/Tm³⁺ samples exhibited intense green, yellowish-green and blue emission, respectively.

Catechin tuned magnetism of Gd-doped orthovanadate through morphology as T1-T2 MRI contrast agents

Tetragonal (t)-LaVO₄ has turned out to be a potential host for luminescent materials. Synthesis of t-LaVO₄ till date has been based on chelating effect of EDTA making it not ideal for bioimaging applications. An alternative was proposed by us through the use of catechin. In recent times there is interest for new MRI contrast agents that can through appropriate doping function both as MRI contrast and optical/upconversion materials. It is generally believed that under appropriate doping, t-LaVO₄ would be a better upconversion material than monoclinic (m)-LaVO₄. Based on these postulations, this work explores the use of gadolinium doped t-LaVO₄ as an MRI contrast agent. From literature, gadolinium oxide is a good T₁ contrast agent. Through this work, using catechin as a template for the synthesis of Gd doped t-LaVO₄, we demonstrate the possible use as a T₁ contrast agent. Interestingly, as the catechin concentration changes, morphology changes from nanorods to square nanoplates and spheres. In this process, a switch from T₁ to T₂ contrast agent was also observed. Under optimal concentration of catechin, with a rod shaped Gd doped t-LaVO₄ an r₂/r₁ value of 21.30 was observed. Similarly, with a spherical shape had an r₂/r₁ value of 1.48 was observed.

The progress of single-band upconversion nanomaterials

An overview of the recent progresses in realizing single-band UC emission through different methods and the related mechanisms are given for the first time. The challenges and future perspectives of these novel NMs are stated.

Design and synthesis of sugar-benzohydrazides: low molecular weight organogelators

A novel class of methyltriglycol benzohydrazide based N-glycosylamines containing long alkyl chain derivatives were synthesized in good yield and characterized using NMR (¹H and ¹³C) spectral analysis.

Core–shell–shell heterostructures of α-NaLuF4:Yb/Er@NaLuF4:Yb@MF2 (M = Ca, Sr, Ba) with remarkably enhanced upconversion luminescence

Core–shell–shell heterostructures of α-NaLuF₄:Yb/Er@NaLuF₄:Yb@MF₂ (M = Ca, Sr, Ba) exhibit remarkably enhanced upconversion luminescence.

Fluorescent LaVO4:Eu3+ micro/nanocrystals: pH-tuned shape and phase evolution and investigation of the mechanism of detection of Fe3+ ions

LaVO₄:Eu³⁺ micro/nanocrystals with various shapes were hydrothermally synthesized by adjusting the pH of the system at 180 °C for 12 h in the presence of ethylenediaminetetraacetic acid (EDTA).