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Recently, materials revealing the upconversion (UC) phenomenon, which is a conversion of low-energy photons to higher-energy ones, have attracted considerable attention in luminescence thermometry due to the possibility of precise and remote optical thermal sensing. The most widely studied type of luminescent thermometry uses a ratiometric approach based on changes in the UC luminescence intensity, mainly of lanthanide ions' thermally coupled energy levels. In this work, NaYF4:Ho3+@NaYF4, and NaYF4:Ho3+, Er3+@NaYF4 nanoparticles (NPs) were synthesized by the controlled reaction in oleic acid and octadecene at 573 K. The obtained nanoparticles had hexagonal structures, oval shapes, and average sizes of 22.5 ± 2.2 nm and 22.2 ± 2.0 nm, respectively. The spectroscopic properties of the products were investigated by measurements of the UC emission under 1151 nm laser excitation in the temperature range between 295 to 378 K. The sample doped with Ho3+ and Er3+ ions showed unique behavior of enhancing emission intensity with the temperature. The relative sensitivity determined for the NPs containing Ho3+ and Er3+ ions, reached the maximum value of 1.80%/K at 378 K. Here, we prove that the NaYF4:Ho3+, Er3+@NaYF4 system presents unique and excellent optical temperature sensing properties based on the luminescence intensity ratios of the near-infrared bands of both Ho3+ and Er3+ ions. [ABSTRACT FROM AUTHOR]

Rare earth phosphate nanomaterials doped with lanthanide ions (Yb 3+ , Ho 3+ , Er 3+ , Tm 3+ , Tb 3+ and Eu 3+ ) showing upconversion (UC) luminescence may play an important role in photonics, optics, electronics and in biomedical diagnostics. Year by year, the significance of rare earth compounds increases. Here, we present structural, morphological and spectroscopic investigations on REPO 4 nanoparticles, which were successfully synthesized by the co-precipitation method followed by annealing at 1000°C. Obtained tetragonal (YPO 4 , LuPO 4 ) and monoclinic (LaPO 4 , GdPO 4 ) nanocrystals were single phase and homogeneous, with dimensions not exceeding 75 nm. These samples exhibited strong luminescence when excited in NIR range (975–978 nm) and the UC mechanisms were proposed. After initial photon absorption by Yb 3+ ions, the energy transfer (ET) to emitting ions (Ho 3+ , Er 3+ , Tm 3+ , Tb 3+ , Eu 3+ ) occurred. Luminescence rise and decay times were short with the exception for Tb 3+ and Eu 3+ ions, which showed up to 5 ms long luminescence. Dependencies of integral luminescence intensity on laser energy indicated that, most of the transitions were two-photon what is typical value for this kind of ions. However, some of transitions were three- and even four-photon (especially in Tm 3+ ions) and some of slope values were lower than two, what was caused by the saturation and local thermal effects. [ABSTRACT FROM AUTHOR]

Up-conversion luminescence of materials doped with lanthanide ions (Ln 3+ ) has attracted much attention in the last few years as a result of their promising applications in many areas, such as in solar cells, biomedicine or forensic sciences. Herein we demonstrate the up-conversion properties of GdOF nanocrystals doped with Yb 3+ /Ho 3+ , Yb 3+ /Er 3+ and Yb 3+ /Tm 3+ pairs of ions. The method of synthesis, based on the sol–gel process, allowed us to obtain single-phase and homogeneous nanomaterial with the desired elemental composition. Spectroscopic studies indicated efficient and broad absorption of the materials, in the range of 900–1000 nm, with the maximum at 972 nm, leading to intense up-conversion with three basic colors: blue (Tm 3+ ), green (Ho 3+ ) and red (Er 3+ ). This also confirmed energy transfer between the Yb 3+ and Ln 3+ co-dopants. Luminescence decay measurements showed a short lifetime of Ln 3+ excited states. Determined dependences of integral luminescence intensity on the laser energy confirmed the presence of the energy transfer up-conversion (ETU) mechanism responsible for the registered luminescence as well as the “saturation effect”. [ABSTRACT FROM AUTHOR]

A series of Er 3+ -TiO 2 , Yb 3+ -TiO 2 and Er 3+ /Yb 3+ -TiO 2 photocatalysts were obtained via sol–gel method, using lanthanides precursor ranging from 0.25 to 10 mol%. The experiments demonstrated that phenol in aqueous solutions was successfully degraded under visible light ( λ > 450 nm) using Er/Yb-TiO 2 . The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS), UV–vis absorption measurement, BET surface area analysis and luminescent spectroscopy. XPS analysis revealed that erbium and ytterbium were present in the form of oxides. The sample showing the highest photoactivity was in the form of anatase, its surface area equalled to 125 m 2 /g, average crystals size was 13 nm, and it was prepared introducing 1 mol% of Yb 3+ into reaction medium. 3 h of irradiation resulted in 89% of phenol degradation under visible light. Action spectra analysis performed for the selected Er/Yb-TiO 2 samples, revealed that irradiation from 420 to 475 nm is responsible for visible light photoactivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] RE doping enhanced the photocatalytic activity under visible irradiation. [•] Acetic acid oxidation over RE-TiO2 under Vis light leads to formation of CO2. [•] All rare earth metals are present in the form of oxides (RE2O3) at the TiO2 surface. [•] RE-TiO2 could be excited under visible light in the range from 420 to 450nm. [ABSTRACT FROM AUTHOR]

A series of Er-, Yb-, Ho-, Tb-, Gd-, Pr-TiO 2 nanotubes (RE-NTs) was prepared via an electrochemical method. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis absorption, scanning electron microscopy (SEM) and luminescent spectroscopy. The experiments demonstrated that toluene in the gas phase was successfully degraded under visible light (LEDs λ max = 465 nm) using RE-NTs. In the presence of the most active sample (Ho-NTs), the photodegradation of toluene reached 30% after 60 min of vis irradiation. To investigate the localization of RE in the TiO 2 structure, computer simulations were performed using the plane-wave-based Vienna ab-initio simulation package (VASP) implementing spin-polarized density-functional theory (DFT) and the generalized gradient approximation (GGA). It is proposed that during the electrochemical process, TiO 2 systems with new Ho-f states below the conduction band of TiO 2 is formed. The photocatalytic activity under Vis irradiation is attributable not to OH but to other forms of reactive oxygen species (O 2 − , HO 2 , H 2 O 2 ). [ABSTRACT FROM AUTHOR]

In this paper, the UV sensitive optically active cellulose fibers contained of 0.5% w/w Sr 2 CeO 4 , Gd 4 O 3 F 6 :5%Eu 3+ and CeF 3 :5%Tb 3+ with respectively blue, red and green emission are described. The fibers were formed from an 8% by weight cellulose spinning solution in N-methylmorpholine-N-oxide (NMMO). The modifiers were chosen because of their specific color of emitted light. Photoluminescent particles were introduced into the polymer matrix during the dissolution process of cellulose in NMMO. The emission intensity and excitation energy of the final cellulosic luminescent products were examined by photoluminescence spectroscopy. The degree of dispersion of the nanoparticles in the polymer matrix was evaluated using transmission electron microscopy (TEM). The influence of modifier's particles on the mechanical properties of the fibers was determined. [ABSTRACT FROM AUTHOR]

Modification with rare-earth (RE) metals has emerged as an important approach for enhancing the properties of titanium dioxide. Herein, the visible-light photocatalytic activity of RE-TiO 2 (RE: Tm, Er, Nd, Dy, Lu, La, Ho, Pr, Tb, Sc, Ce, Yb, Sm, Gd, Y, or Eu) was investigated using a combination of computer simulations and experimental techniques. The RE-TiO 2 photocatalysts were characterised using advanced experimental techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, luminescence, diffuse reflectance spectroscopy, and specific surface area measurements. Furthermore, a quantitative structure–activity relationship analysis was conducted by applying a partial least-squares machine learning algorithm. The Ho-TiO 2 sample exhibited the highest photocatalytic activity under visible-light irradiation. Notably, the observed activity was not due to an up-conversion process, originating instead from slight bandgap narrowing caused by new sub-bandgap states from the RE 4 f levels. [Display omitted] • The visible-light photoactivity of rare-earth-metal-doped TiO 2 was investigated. • Photocatalysts based on all rare-earth elements, except Pm, were synthesised. • A combination of computational and experimental techniques was applied. • Ho-TiO 2 achieved the highest photocatalytic activity under visible-light irradiation. • Sub-bandgap states from the 4 f levels of the doped metal caused bandgap narrowing. [ABSTRACT FROM AUTHOR]

[Display omitted] The right choice of synthesis route for upconverting nanoparticles (UCNPs) is crucial for obtaining a well-defined product with a specific application capability. Thus we decided to compare the physicochemical, cytotoxic, and temperature-sensing properties of UCNPs obtained from different rare earth (RE) ions, which has been made for the first time in a single study. The core/shell NaYF 4 :Yb3+,Er3+/NaYF 4 UCNPs were obtained by reaction in a mixture of oleic acid and octadecene, and their highly stable water colloids were prepared using the ligand-free modification method. Both oleate-capped and ligand-free UCNPs exhibited a bright upconversion emission upon 975 nm excitation. Moreover, slope values, emission quantum yields, and luminescence lifetimes confirmed an effective energy transfer between the Yb3+ and Er3+ ions. Additionally, the water colloids of the UCNPs showed temperature-sensing properties with a good thermal sensitivity level, higher than 1 % K−1 at 358 K. Evaluation of the cytotoxicity profiles of the obtained products indicated that cell viability was decreased in a dose-dependent manner in the analyzed concentration range. [ABSTRACT FROM AUTHOR]

The luminescent GdVO 4 :Eu 3+ 5%@SiO 2 @NH 2 core@shell nanomaterials were obtained via co-precipitation method, followed by hydrolysis and co-condensation of silane derivatives: tetraethyl orthosilicate and 3-aminopropyltriethoxysilane. Their effect on human erythrocytes sedimentation and on proliferation of human lung microvascular endothelial cells was examined and discussed. The luminescent nanoparticles were synthesized in the presence of polyacrylic acid or glycerin in order to minimalize the agglomeration and excessive growth of nanostructures. Surface coating with amine functionalized silica shell improved their biocompatibility, facilitated further organic conjugation and protected the internal core. Magnetic measurements revealed an enhanced T 1 -relaxivity for the synthesized GdVO 4 :Eu 3+ 5% nanostructures. Structure, morphology and average grain size of the obtained nanomaterials were determined by X-ray diffraction, transmission electron microscopy and dynamic light scattering analysis. The qualitative elemental composition of the nanomaterials was established using energy-dispersive X-ray spectroscopy. The spectroscopic characteristic of red emitting core@shell nanophosphors was completed by measuring luminescence spectra and decays. The emission spectra revealed characteristic bands of Eu 3+ ions related to the transitions 5 D 0 - 7 F 0,1,2,3,4 and 5 D 1 - 7 F 1 . The luminescence lifetimes consisted of two components, associated with the presence of Eu 3+ ions located at the surface of the crystallites and in the bulk. [ABSTRACT FROM AUTHOR]

A facile coprecipitation reactionbetween Ce3+, Gd3+, Tb3+, and F–ions, in thepresence of glycerine as a capping agent, led to the formation ofultrafine, nanocrystalline CeF3:Tb3+5%, Gd3+5% (LnF3). The as-prepared fluoride nanoparticleswere successfully coated with an amine modified silica shell. Subsequently,the obtained LnF3@SiO2@NH2nanostructureswere conjugated with 4-ethoxybenzoic acid in order to prove the possibilityof organic modification and obtain a new functional nanomaterial.All of the nanophosphors synthesized exhibited intense green luminescenceunder UV light irradiation. Based on TEM (transmission electron microscopy)measurements, the diameters of the cores (≈12 nm) and core/shellparticles (≈50 nm) were determined. To evaluate the cytotoxicactivity of the nanomaterials obtained, their effect on human erythrocyteswas investigated. LnF3nanoparticles were bound to theerythrocyte membrane, without inducing any cytotoxic effects. Aftercoating with silica, the nanoparticles revealed significant cytotoxicity.However, further functionalization of the nanomaterial with −NH2groups as well as conjugation with 4-ethoxybenzoic acid entaileda decrease in cytotoxicity of the core/shell nanoparticles. [ABSTRACT FROM AUTHOR]