Search Results (8)

Thickness-controlled, easily patterned upconversion (UC) nanofilms are essential for high-precision optoelectronic devices, but challenges such as imprecise thickness control and low fluorescence intensity hinder their application. High-performance lanthanide-doped sodium yttrium fluoride UC materials are typically available in powder form, making direct integration into advanced devices difficult. Although physical vapor deposition (PVD) enables precise film formation, it often produces poor crystalline structures and weak fluorescence. To overcome these limitations, integrating non-noble plasmonic Ni with surface plasmon resonance to enhance fluorescence intensity is a promising yet understudied strategy, likely due to Ni’s ultraviolet resonant wavelength and oxidation susceptibility. This study introduces an integrated Ni-UC nanofilm design, combining an ultrathin Ni layer with a NaYF₄:Tm, Yb UC layer via PVD, followed by post-annealing. Annealing at 500 °C transforms the UC layer into a hexagonal-phase crystal structure while protecting the Ni layer from oxidation. The unannealed UC nanofilm showed no fluorescence, whereas the annealed UC nanofilm displayed clear peaks at 476, 648, and 699 nm. Notably, the integrated Ni-UC nanofilm exhibited fluorescence intensities 5.29, 4.43, and 4.29 times higher at these wavelengths, respectively. Additionally, the integrated design exhibited high transparency and stability, highlighting its protective benefits. These results underscore the potential of the integrated Ni-UC nanofilm for advanced optoelectronics and sensing technologies, offering enhanced fluorescence, micro-processing compatibility, and robust performance in a cost-effective, non-noble plasmonic system. Full article

Thermally enhanced upconversion luminescence (UCL), also known as negative thermal quenching of UCL, denotes a continuous increase in the UCL emission intensity of a particular phosphor with a rising temperature. In recent years, the thermal enhancement of UCL has attracted extensive research attention, with numerous reports detailing this effect in phosphors characterized by varying particle sizes, architectures, and compositions. Several hypotheses have been formulated to explain the underlying mechanisms driving this thermal enhancement. This paper rigorously examines thermally enhanced UCL in fluoride nanoparticles by addressing two key questions: (1) Is the thermal enhancement of UCL an intrinsic feature of these nanoparticles? (2) Can the proposed mechanisms explaining this enhancement be unequivocally supported by the existing literature? Upon analyzing a compilation of experimental observations alongside the concurrent phenomena occurred during spectral measurements, it is postulated that thermally enhanced UCL intensity is likely a consequence of multiple extrinsic factors operating simultaneously at elevated temperatures, rather than being an intrinsic property of nanoparticles. These factors include moisture desorption, laser-induced local heating, and lattice thermal expansion. The size-dependent properties of nanoparticles, such as surface-to-volume ratio, thermal expansion coefficient, and quantum yield, are the fundamental reasons for the size-dependent thermal enhancement factor of UCL. Temperature-dependent emission spectral intensity is not a dependable indicator for assessing the thermal quenching properties of phosphors. This is because it is influenced not only by the phosphor’s quantum yield, but also by various extrinsic factors at high temperatures. The nonlinear nature of UCL further magnifies the impact of these extrinsic factors. Full article

Rare-earth-doped fluoride nanoparticles (NPs), known for their tunable luminescence and high chemical stability, hold significant potential for applications in X-ray imaging and radiation dose monitoring. However, most research has primarily focused on lanthanide-doped NaLuF₄ or NaYF₄ nanosystems. In this work, Cs₂NaYF₆:Tb NPs with enhanced X-ray excited optical luminescence (XEOL) intensity were developed. Our results indicate that low oleic acid (OA) content and a high [Cs⁺]/[Na⁺] ratio favor the formation of pure cubic-phase Cs₂NaYF₆:Tb NPs. Cs₂NaYF₆:Tb NPs were successfully fabricated into thin films and employed as nanoscintillator screens for X-ray imaging, achieving a high spatial resolution of 20.0 Lp/mm. Beyond X-ray imaging applications, Cs₂NaYF₆:Tb NPs were also explored for spermine detection, demonstrating high sensitivity with a detection limit of 0.44 μM (under X-ray excitation) within a concentration range of 0–60 μM. These findings may contribute to the development of novel lanthanide-doped fluoride nanoscintillators for high-performance X-ray imaging and molecular sensing. Full article

In this study, the mechanochemical preparation of nanocrystalline CaF₂:Sm³⁺ by ball milling calcium acetate hydrate, samarium (III) acetate hydrate, and ammonium fluoride is reported. The photoluminescence of the as-prepared CaF₂:Sm³⁺ shows predominantly Sm^3+ 4G_5/2 → ⁶H_J(J = 5/2, 7/2, 9/2, and 11/2) f-f luminescence, but intense electric dipole allowed 4f⁵5d (T_1u) → 4f^6 7F₁ (T_1g) luminescence by Sm²⁺ was generated upon X-irradiation. In comparison with the co-precipitated CaF₂:Sm³⁺, the conversion of Sm³⁺$\to$ Sm²⁺ in the ball-milled sample upon X-irradiation is significantly lower. Importantly, the present results indicate that the crystallite size and X-ray storage phosphor properties of the lanthanide-doped nanocrystalline CaF₂ can be modified by adjusting the ball milling time, dopant concentration and post-annealing treatment, yielding crystallite sizes as low as 6 nm under specific experimental conditions. Full article

Lanthanide ions possess various emission channels in the near-infrared region that are well known in bulk crystals but are far less studied in samples with nanometric size. In this work, we present the infrared spectroscopic characterization of various Nd-doped fluoride and sesquioxide nanocrystals, namely Nd:Y₂O₃, Nd:Lu₂O₃, Nd:Sc₂O₃, Nd:YF₃, and Nd:LuF₃. Emissions from the three main emission bands in the near-infrared region have been observed and the emission cross-sections have been calculated. Moreover, another decay channel at around 2 μm has been observed and ascribed to the ⁴F_3/2→⁴I_15/2 transition. The lifetime of the ⁴F_3/2 level has been measured under LED pumping. Emission cross-sections for the various compounds are calculated in the 1 μm, 900 nm, and 1.3 μm regions and are of the order of 10⁻²⁰ cm² in agreement with the literature results. Those in the 2 μm region are of the order of 10⁻²¹ cm². Full article

Lanthanide-doped hexagonal β-NaYF₄ crystals have received much attention in recent years due to their excellent photoluminescence properties. However, lanthanide-doped β-NaYF₄ crystals with micron and submicron scales as well as uniform morphology have received less attention. In this study, Eu³⁺-doped β-NaYF₄ (β-NaYF₄:Eu³⁺) crystals of micron and submicron size scales were synthesized using the solvothermal method with ethylene glycol as the solvent. The β-NaYF₄:Eu³⁺ crystals were highly crystallized. A comparison of the characteristics of the β-NaYF₄:Eu³⁺ crystals synthesized with and without the use of oleic acid as a surfactant was conducted. It was found that the utilization of oleic acid as a surfactant during their synthesis greatly decreased their particle size from micron to submicron scale, while adding a small amount of ethanol further reduced their particle size. In addition, they exhibited much smoother surfaces and more uniform morphologies, which were hexagonal prism bipyramids. The microstructural characteristics and photoluminescence properties of the β-NaYF₄:Eu³⁺ crystals were studied in detail. Results showed that β-NaYF₄:Eu³⁺ crystals prepared with the aid of oleic acid as a surfactant during their synthesis exhibited stronger photoluminescence. Full article

Due to the high atomic number of lutetium and the low phonon energy of the fluoride matrix, Lu-based fluoride nanoparticles doped with active lanthanide ions are potential candidates as bioprobes in both X-ray computed tomography and luminescent imaging. This paper shows a method for the fabrication of uniform, water-dispersible Eu³⁺:(H₃O)Lu₃F₁₀ nanoparticles doped with different Eu contents. Their luminescent properties were studied by means of excitation and emission spectra as well as decay curves. The X-ray attenuation capacity of the phosphor showing the highest emission intensity was subsequently analyzed and compared with a commercial contrast agent. The results indicated that the 10% Eu³⁺-doped (H₃O)Lu₃F₁₀ nanoparticles fabricated with the proposed polyol-based method are good candidates to be used as dual probes for luminescent imaging and X-ray computed tomography. Full article

The modeling and design of fiber lasers facilitate the process of their practical realization. Of particular interest during the last few years is the development of lanthanide ion-doped fiber lasers that operate at wavelengths exceeding 2000 nm. There are two main host glass materials considered for this purpose, namely fluoride and chalcogenide glasses. Therefore, this study concerned comparative modeling of fiber lasers operating within the infrared wavelength region beyond 2000 nm. In particular, the convergence properties of selected algorithms, implemented within various software environments, were studied with a specific focus on the central processing unit (CPU) time and calculation residual. Two representative fiber laser cavities were considered: One was based on a chalcogenide–selenide glass step-index fiber doped with trivalent dysprosium ions, whereas the other was a fluoride step-index fiber doped with trivalent erbium ions. The practical calculation accuracy was also assessed by comparing directly the results obtained from the different models. Full article