Multifunctional cellulose fibers: Intense red upconversion under 1532 nm excitation and temperature-sensing properties

Enhancing NIR-II Upconversion Monochromatic Emission for Temperature Sensing

The upconversion luminescence (UCL) in the second near-infrared window (NIR-II) is highly attractive due to its excellent performance in high-resolution bioimaging, anticounterfeiting, and temperature sensing. However, upconvertion nanoparticles (UCNPs) are normally emitted in visible light, potentially impacting the imaging quality. Here, a monochromatic Er3+-rich (NaErF4:x%Yb@NaYF4) nanoparticles with excitation at 1532 nm and emission at 978 nm is proposed, both situated in the NIR-II region. The proper proportion of Yb3+ ions doping has a positive effect on the NIR-II emission, by enhancing the cross relaxation efficiency and accelerating the energy transfer rate. Owing to the interaction between the Er3+ and Yb3+ is inhibited at low temperatures, the UCL emission intensities at visible and NIR-II regions show opposite trend with temperature changing, which establishes a fitting formula to derive temperature from the luminous intensity ratio, promoting the potential application of UCL in NIR-II regions for the temperature sensing.

Luminescent/Temperature-Sensing Properties of Multifunctional Rare-Earth Upconversion Kevlar Nanofiber Composite under 1550 nm

The unique properties of upconversion nanoparticles (UCNPs) are responsible for their diverse applications in photonic materials, medicine, analytics, and energy conversion. In this study, water-soluble rare-earth upconversion nanomaterials emitting green, yellow, and red light under 1550 nm excitation were synthesized. These nanomaterials were then integrated into water-soluble Kevlar nanofibers (KNFs) to fabricate ultra-thin composite films exhibiting favorable mechanical characteristics. The characterization of the products, along with their luminescent, mechanical, and temperature-sensing properties, was examined. The results indicate that the composite material exhibited varying colors based on the doped nanoparticles when subjected to 1550 nm excitation. The composite showed highly sensitive temperature-sensing properties, excellent luminescent characteristics, and superior mechanical strength. This study suggests that KNFs are effective carriers of UCNPs. This study offers a reference for the utilization of rare-earth upconversion in anti-counterfeiting displays, wearable health monitoring, and remote temperature sensing.

The Art of Nanoparticle Design: Unconventional Morphologies for Advancing Luminescent Technologies

The advanced design of rare-earth-doped (RE-doped) fluoride nanoparticles has expanded their applications ranging from anticounterfeiting luminescence and contactless temperature measurement to photodynamic therapy. Several recent studies have focused on developing rare morphologies of RE-doped nanoparticles. Distinct physical morphologies of RE-doped fluoride materials set them apart from contemporary nanoparticles. Every unusual structure holds the potential to dramatically improve the physical performance of nanoparticles, resulting in a remarkable revolution and a wide range of applications. This comprehensive review serves as a guide offering insights into various uniquely structured nanoparticles, including hollow, dumbbell-shaped, and peasecod-like forms. It aims to cater to both novices and experts interested in exploring the morphological transformations of nanoparticles. Discovering new energy transfer pathways and enhancing the optical application performance have been long-term challenges for which new solutions can be found in old papers. In the future, nanoparticle morphology design is expected to involve more refined microphysical methods and chemically-induced syntheses. Targeted modification of nanoparticle morphology and the aggregation of nanoparticles of various shapes can provide the advantages of different structures and enhance the universality of nanoparticles.

The use of energy looping between Tm3+ and Er3+ ions to obtain an intense upconversion under the 1208 nm radiation and its use in temperature sensing

The upconversion phenomenon allows for the emission of nanoparticles (NPs) under excitation with near-infrared (NIR) light. Such property is demanded in biology and medicine to detect or treat diseases such as tumours. The transparency of biological systems for NIR light is limited to three spectral ranges, called biological windows. However, the most frequently used excitation laser to obtain upconversion is out of these ranges, with a wavelength of around 975 nm. In this article, we show an alternative - Tm3+/Er3+-doped NPs that can convert 1208 nm excitation radiation, which is in the range of the 2nd biological window, to visible light within the 1st biological window. The spectroscopic properties of the core@shell NaYF4:Tm3+@NaYF4 and NaYF4:Er3+,Tm3+@NaYF4 NPs revealed a complex mechanism responsible for the observed upconversion. To explain emission in the studied NPs, we propose an energy looping mechanism: a sequence of ground state absorption, energy transfers and cross-relaxation (CR) processes between Tm3+ ions. Next, the excited Tm3+ ions transfer the absorbed energy to Er3+ ions, which results in green, red and NIR emission at 526, 546, 660, 698, 802 and 982 nm. The ratio between these bands is temperature-dependent and can be used in remote optical thermometers with high relative temperature sensitivity, up to 2.37%/°C at 57 °C. The excitation and emission properties of the studied NPs fall within 1st and 2nd biological windows, making them promising candidates for studies in biological systems.

Anti-counterfeiting system based on luminescent varnish enriched by NIR- excited nanoparticles for paper security

Up-converting nanoparticles can be a demand for requirements in many areas, including bioimaging and conversion of energy, but also in the battle against counterfeiting. The properties of lanthanide ions make falsification difficult or even impossible using appropriately designed systems. The proposition of such an approach is the NaErF₄:Tm³⁺@NaYF₄ core@shell up-converting nanoparticles combined with transparent varnishes. Given the spectroscopic properties of Er³⁺ ions present in the fluoride matrix, the obtained up-converting nanoparticles absorb light by 808 and 975 nm wavelengths. The intentionally co-doped Tm³⁺ ions enable tuning characteristic green Er³⁺ emission to red luminescence, particularly desirable in anti-counterfeiting applications. The article includes a thorough analysis of structural and morphological properties. Moreover, this work shows that exclusive luminescent properties of NaErF₄:Tm³⁺@NaYF₄ NPs can be given to the transparent varnish, providing an excellent anti-counterfeiting system, revealing red emission under two different excitation wavelengths.