Toward Upconversion (Yb-Er) and near-Infrared (Yb-Ho-Er, Nd-Yb) Thermometry with Sea Urchin Type GdPO4 Nanoarchitectures

In recent years, optical temperature probes operating in the second near-infrared (BW-II) and third near-infrared (BW-III) biological windows have garnered significant attention in the scientific community. For biological applications these probes offer distinct advantages, including enhanced tissue penetration depth, minimal autofluorescence, and a remarkable improvement in imaging sensitivity and spatial resolution. Moving toward theranostic applications, there is a growing demand for the development of materials that integrate both BW-II and BW-III thermometry systems with drug delivery functionalities. In this study, we concentrate on the development of GdPO4 materials, utilizing both hard and sacrificial template routes to synthesize (hollow) GdPO4 porous sea urchin-like particles. We first investigated the development of a Boltzmann-type thermometer utilizing an Yb-Er upconversion system, designed to operate within the physiological temperature range. Our exploration extends to the potential of GdPO4 particles in near-infrared (NIR) thermometry, spanning the first, second, and third biological windows with systems like Yb-Ho-Er, Nd-Yb, and Ho-Yb, respectively. We further examined the temperature impact of the Yb-Ho-Er system on the NIR emission within a biologically relevant setting, using a phantom that replicates biological tissue. Furthermore, we illustrate the successful loading of these materials with doxorubicin (DOX·HCl), a model anticancer drug, showing these particles exhibit pH-dependent DOX release. This demonstrates the versatility of these materials as upconversion and NIR thermometers while simultaneously serving as an on-demand drug carrier. The investigation involves assessing their cytotoxicity on specific human cells (Normal Human Dermal Fibroblasts (NHDFs)), to determine their viability for potential use in biological applications. The study also investigates how effectively loading the particles with DOX enables targeted delivery to a cellular model of lymphoma (Jurkat E6-1), resulting in cell death. This comprehensive analysis highlights the promising potential of GdPO4 particles for medical applications.

Exploring the potential of lanthanide-doped oxyfluoride materials for bright green upconversion and their promising applications towards temperature sensing and drug delivery

The most efficient upconversion (UC) materials reported to date are based on fluoride hosts with low phonon energies, which reduce the amount of nonradiative transitions. In particular, NaYF4 doped with Yb3+ and Er3+ at appropriate ratios is known as one of the most efficient UC phosphors. However, its low thermal stability limits its use for certain applications. On the other hand, oxide hosts exhibit better thermal stability, yet they have higher phonon energies and are thus prone to lower UC efficiencies. As a result, developing host nanomaterials that combine the robustness of oxides with the high upconversion efficiencies of fluorides remains an intriguing prospect. Herein, we demonstrate the formation of ytrrium doped oxyfluoride (YOF:Yb3+,Er3+) particles, which are prepared by growing a NaYF4:Yb3+,Er3+ layer around SiO2 spherical particles and consecutively applying a high-temperature annealing step followed by the removal of SiO2 template. Our interest lies in employing these materials as Boltzmann type physiological range luminescence thermometers, but their weak green emission is a drawback. To overcome this issue, and engineer materials suitable for Boltzmann type thermometry, we have studied the effect of introducing different metal ion co-dopants (Gd3+, Li+ or Mn2+) into the YOF:Yb3+,Er3+ particles, focusing on the overall emission intensity, as well as the green to red ratio, upon 975 nm laser excitation. These materials are explored for their use as ratiometric thermometers, and further also as drug carriers, including their simultaneous use for these two applications. The investigation also includes examining their level of toxicity towards specific human cells - normal human dermal fibroblasts (NHDFs) - to evaluate their potential use for biological applications.

Nucleation and Growth of Bipyramidal Yb:LiYF4 Nanocrystals-Growing Up in a Hot Environment

Lanthanide-doped LiYF₄ (Ln:YLF) is commonly used for a broad variety of optical applications, such as lasing, photon upconversion and optical refrigeration. When synthesized as nanocrystals (NCs), this material is also of interest for biological applications and fundamental physical studies. Until now, it was unclear how Ln:YLF NCs grow from their ionic precursors into tetragonal NCs with a well-defined, bipyramidal shape and uniform dopant distribution. Here, we study the nucleation and growth of ytterbium-doped LiYF₄ (Yb:YLF), as a template for general Ln:YLF NC syntheses. We show that the formation of bipyramidal Yb:YLF NCs is a multistep process starting with the formation of amorphous Yb:YLF spheres. Over time, these spheres grow via Ostwald ripening and crystallize, resulting in bipyramidal Yb:YLF NCs. We further show that prolonged heating of the NCs results in the degradation of the NCs, observed by the presence of large LiF cubes and small, irregular Yb:YLF NCs. Due to the similarity in chemical nature of all lanthanide ions our work sheds light on the formation stages of Ln:YLF NCs in general.

Dual-mode vehicles with simultaneous thermometry and drug release properties based on hollow Y2O3:Er,Yb and Y2O2SO4:Er,Yb spheres

Employing luminescence thermometry in the biomedical field is undeniably appealing as many health conditions are accompanied by temperature changes. In this work, we show our ongoing efforts and results at designing novel vehicles for dual-mode thermometry and pH-dependent drug release based on hollow spheres. Hereby for that purpose, we exploit the hollow Y2O3 and Y2O2SO4 host materials. These two inorganic hollow phosphors were investigated and showed to have excellent upconversion Er3+-Yb3+ luminescence properties and could be effectively used as optical temperature sensors in the physiological temperature range when induced by near-infrared CW light (975 nm). Further, doxorubicin was exploited as a model anti-cancer drug to monitor the pH-dependent drug release of these materials showing that they can be used for simultaneous thermometry and drug delivery applications.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Tuning morphology, surface, and nanocrystallinity of rare earth vanadates by one-pot colloidal conversion of hydroxycarbonates

We show that particle size, morphology, nanocrystallinity, surface area, and defect density of (Y,Eu)VO₄ structures can be tuned by one-pot colloidal conversion of rare earth hydroxycarbonates in water/ethylene glycol (EG) suspensions. Using small angle X-ray scattering, transmission electron microscopy and dynamic light scattering, we show how volume fractions of EG direct the amorphous to crystalline conversion at 1 atm/95 °C by controlling size and aggregation of hydroxycarbonate precursors. A template effect due to a Kirkendall-type conversion occurs for low EG contents, yielding solids with high densities of oxygen defects, as demonstrated by O₂ uptakes in thermogravimetry and X-ray photoelectron spectroscopy profiles. Starting from small and aggregated hydroxycarbonates high-porosity (Y,Eu)VO₄ nanoparticles were produced with expanded unit cells and short-range (<100 Å) crystalline ordering. We explored the effects of synthesis on the textural, microstructure, and defects of (Y,Eu)VO₄ solids, which were further correlated to the spectroscopic profiles of Eu³⁺-activated samples. We show that the ratios between Eu^{3+ 5}D₀ internal quantum yields and particle diameters can be directly correlated to the particle surface areas, opening new perspectives for theoretical detailing of f-f luminescence in YVO₄ solids, and enabling accurate tuning of structure and applicability of colloidal vanadate nanoparticles for sensing and catalysis applications.

Harnessing host–guest interactions to control structure at the nanoscale

Host–guest interactions mediate many chemical and biochemical transformations and are extensively exploited in a number of industrially-relevant chemical processes. Many porous inorganic (e.g., zeolite) and molecular (e.g., metal-organic framework) hosts engage reagents in their environment through selective host–guest interactions. While researchers frequently capitalize on host–guest interactions to sequester chemical species or to catalyze reactions, these interactions can also be used to direct nanomaterial synthesis. In this Perspective we highlight the promise and opportunities for harnessing host–guest interactions to control the structure and dimensionality of materials. We focus our discussion on emerging strategies in soft chemistry and promising new directions which use porous ionic solids to direct the growth of complex nanoscale dimers and Janus nanoparticles.

NIR light-activated upconversion semiconductor photocatalysts

Harvesting of near infrared (NIR) light in the abundant and environmentally friendly solar spectrum is particularly significant to enhance the utilization rate of the cleanest energy on earth. Appreciating the unique nonlinear optical properties of upconversion materials for converting low-energy incident light into high-energy radiation, they become the most promising candidates for fabricating NIR light-active photocatalytic systems by integrating with semiconductors. The present review summarizes recent NIR light-active photocatalytic systems based on a sequence of NaYF₄-based, fluoride-based, oxide-based and Ln³⁺ ion-doped semiconductor-based photocatalysts for degradation of organic molecules. In addition, we provide an in-depth analysis of various photocatalytic mechanisms and enhancement effects for efficient photo-redox performance of different upconversion semiconductor photocatalysts. We envision that this review can inspire multidisciplinary research interest in rational design and fabrication of efficient full-spectrum active (UV-visible-NIR) photocatalytic systems and their wider applications in solar energy conversion.

Lanthanoid-Doped Phosphate/Vanadate Mixed Hollow Particles as Ratiometric Luminescent Sensors

Rare earth (RE) phosphates and vanadates are structurally similar compositions that display distinct but complementary luminescent properties. The properties of these phosphors can be combined in REPO₄-REVO₄ heterostructures during the development of new sensing technologies for biological applications. This work presents the synthesis of hollow RE phosphate/vanadate colloidal particles and evaluates their applicability as luminescent markers. Hydrothermal treatments of RE hydroxycarbonate particles in the presence of the PO₄^3- and VO₄^3- precursors afforded the final REPO₄-REVO₄ solids in a two-step template synthesis. We converted precursor hydroxycarbonate particles into the final heterostructures and characterized their structure and morphology. According to our detailed study into the spectroscopic properties of Eu³⁺-doped particles and their luminescence response to several species, the presence of the phosphate and vanadate phases in a single particle provided different chemical environments and enabled the design of a ratiometric approach to detect H₂O₂. These results open new perspectives for the development of new intracellular luminescent markers.

Facile synthesis of flower-shaped Au/GdVO4:Eu core/shell nanoparticles by using citrate as stabilizer and complexing agent

The synthesis of metal/rare-earth core/shell hetero-nanostructures through directly coating rare-earth compound onto the surface of Au nanocrystals.

Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials

Rare-earth carbonate nano- and micro-materials are reviewed, focusing on factors that influence the morphology and luminescence, as well as their applications as precursors and sacrificial templates for other materials.

Morphology-controlled assembly and enhanced emission of fluorescence in organic nanospheres and microrods based on 1,2-diphenyl-4-(4-dibenzothienyl)phenyl-1,3-cyclopentadiene

Fluorescent organic micro/nanostructures of 1,2-diphenyl-4-(4-dibenzothienyl)phenyl-1,3-cyclopentadiene have been prepared via controlling the solvent composition.

(Y,Tb,Eu)2O3 monospheres for highly fluorescent films and transparent hybrid films with color tunable emission

(Y,Tb,Eu)₂O₃ monospheres were employed as building blocks for highly fluorescent films and as dispersion fillers for transparent polymer films.