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This paper reports the spectroscopic properties of up-converting NaLuF4 materials doped with Yb3+, Er3+ and with different amount of Ho3+ ions. The products were synthesized by simple hydrothermal route and their structural properties were carefully examined by using X-ray diffraction and scanning electron microscopy. The relation between the changing amount of Ho3+ ions and spectroscopic properties was investigated by luminescence measurements. The recorded emission spectra exhibited seven characteristic bands under excitation with 975 nm laser beam, with the most intense peaks at 550 and 650 nm. The observed in the emission spectra peaks resulted from overlapped emission of Er3+ and Ho3+ ions. The dependencies between laser power density and integral luminescence intensity were measured. Determined on their basis number of photons responsible for the observed up-conversion and calculated luminescence lifetimes allowed determining the mechanism of the up-conversion process, in detail.

The article describes the properties of LuF3 and NaLuF4 fluorides doped with Yb3+ and Er3+ or Tm3+ ions, their comparison and application in latent fingermarks imaging. The single-phase materials were successfully synthesized by the hydrothermal method. They exhibited up-conversion (UC) phenomenon under excitation by the near-infrared (NIR) radiation at 975 nm. Under excitation, the energy transfer between Yb3+ and Er3+ or Tm3+ ions occurred and emissions in the visible range were recorded (green or blue for Er3+ or Tm3+ dopants respectively). The luminescence decays of as-prepared samples were measured allowing the calculation of luminescence lifetimes. The dependencies of integrated UC intensity on laser power density were measured for the obtained samples, revealing up to three-photon process for Yb3+ and Tm3+ co-doped and two-photon process for Yb3+ and Er3+ co-doped materials. Furthermore, up-converting lutetium fluorides synthesized in this report were successfully used to visualize latent fingermarks on various non-porous surfaces.

In this paper, we demonstrate the enhancement of up-conversion luminescence of LaVO4:Yb3+/Ln3+ (Ln = Ho, Er and Tm) nanoparticles by co-doping this material with alkaline ions M2+ (M = Mg, Sr and Ba) and Sn4+ ions. The samples were synthesised by a Pechini-type sol-gel method and annealed at 600 °C for 2 h in an air atmosphere. Their structure and morphology were characterised by powder X-ray diffraction, transmission electron microscopy and inductively coupled plasma atomic emission spectroscopy, revealing that the nanomaterials were single-phase and homogeneous with the dimensions of about 20 nm and co-doped ions were successfully incorporated in LaVO4 lattice. Laser spectroscopy measurements (emission and excitation spectra, luminescence lifetimes and luminescence intensity dependences on power density) indicated that under NIR excitation (about 980 nm) nanoparticles showed bright up-conversion luminescence. After co-doping with M2+/Sn4+ ions, the phase structure of the host lattice remained unaltered, but the cell parameters slightly changed, as these ions can occupy La3+ sites or interstitial positions and change local crystal field. As a result, spectroscopic properties were changed, and emission intensity was enhanced in all samples, making these nanoparticles more attractive in, for instance, photonics or electronic industry.

A series of CaF2-doped phosphors was synthesized in situ in hydrothermal conditions (in a DAB- 2 reactor), in the presence of sodium citrate as a complexing agent preventing premature precipitation. The materials were doped with Yb3+/Er3+ pair of ions, which resulted in up-conversion emission. Additionally, Mn2+ ions were incorporated into the structure of the CaF2 to analyse their influence on the chromaticity of the luminescence colour, in view of their application in bioimaging. Detailed structural analysis showed that the structure of the nanoparticles obtained resembled the core@shell like structure. Finally, the emission colour was tuned from green to orange – red. It was confirmed that the quantity of Mn2+ ions incorporated in the CaF2 matrix definitely differs from the expected one. The real concentration of Mn2+ ions in the structure is frequently ignored, which leads to incorrect conclusions. For this reason, a detailed structural and spectroscopic analysis was conducted and the effect of Mn2+ ions on the structure and the average size of the CaF2-doped phosphors was studied. Moreover, the in vitro cytotoxicity of the nanoparticles was evaluated. Obtained results showed that CaF2:15%Yb3+, 2%Er3+, 2.6%Mn2+ reduces cell viability of fibroblast at lower concentrations (50, 100 and 200 μg/ml) than CaF2:15%Yb3+, 2%Er3+ (200 μg/ml). Moreover, CaF2:15%Yb3+, 2%Er3+ caused increase of the fibroblast proliferation rate at the lowest tested concentration (10 μg/ml).

Lithium lanthanum praseodymium tetraphosphates nanopowders, LiLa 1−x Pr x (PO 3 ) 4 , where x = 0.01–1, were prepared by wet-chemistry synthesis route. The structure and morphology of phosphates were analyzed by collecting X-ray diffraction patterns, Raman and FT-IR spectra. The obtained materials were composed of submicron crystals in the elongated forms and plates. The monoclinic structure of the crystals with the space group C 2/ c was assigned for all investigated compositions. The decrease of unit cell parameters with the increase of praseodymium concentration, due to the lower ionic radius of the Pr 3+ as compared to the La 3+ cations, was evidenced. Spectroscopic properties of the LiLa 1−x Pr x (PO 3 ) 4 powders were analyzed in details on the basics of the absorption, excitation, and emission spectra with luminescence lifetimes measurements. The intraconfigurational 4 f 2 transitions were observed under blue (λ = 440 nm) and UV (λ = 212 nm) excitation. The luminescence characteristic of the samples was dependent on the concentration of the Pr 3+ ions in the host material. Significant concentration quenching in the whole range of investigated samples was observed leading to barely seen emission of the LiPr(PO 3 ) 4 crystals.

Down- and upconversion luminescence phenomena from YBO3 materials doped by Yb3+ and Tb3+ ions were observed and investigated. Materials described in the article were synthesized by a sol-gel method. Two series of products were prepared: with changed molar concentrations of Yb3+ or Tb3+ ions in the range from 1 to 30%. This way of doping was chosen to analyse the influence of ions concentrations on luminescence and to find samples with the most intense emission. Structural and morphological properties of the obtained materials were analysed on the basis of X-ray diffraction, infrared spectroscopy and by collecting images of samples from transmission electron microscope. The products were pure and well crystallized, showing monoclinic structure with C2/c space group. Spectroscopic properties of the YBO3:Yb3+,Tb3+ materials were investigated by measurements of excitation spectra in the ultraviolet and near infrared range; emission spectra in the visible range; luminescence decays and dependencies of integral luminescence intensity on pumping laser energy. Based on careful studies of the obtained results, mechanisms responsible for the processes observed in these materials were proposed and explained.

LaF3:Eu3+ nanoparticles were synthesized by a co-precipitation method using glycerine or Triton X-100 as a surfactant. Structure and morphology of the nanocrystals were characterized on the basis of X-ray diffraction and transmission electron microscopy. The average crystallite size was calculated from the full-width at half-maximum of the diffraction peaks using the Scherrer equation. The nanopowders obtained were composed of nanocrystallites with the average size 9 ± 1 nm and 13 ± 2 nm for LaF3:5%Eu3+ prepared using glycerine or Triton X-100, respectively. An interesting result was, that using glycerine provided partial reduction of the Eu3+ to Eu2+ and hence white luminescence under UV excitation. The luminescent properties of the nanoparticles were investigated by excitation and emission spectra. Luminescence lifetimes were analyzed and discussed and the chromaticity coordinates were calculated. The magnetic analysis of the nanophosphors obtained was conducted in order to observe the influence of the Eu2+ ions on the magnetic properties of the samples prepared. The magnetic properties of lanthanum fluorides depend on the parameters of those rare earth elements and the substitutions.

Up-conversion luminescence of materials doped with lanthanide ions (Ln3+) 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 Yb3+/Ho3+, Yb3+/Er3+ and Yb3+/Tm3+ 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 (Tm3+), green (Ho3+) and red (Er3+). This also confirmed energy transfer between the Yb3+ and Ln3+ co-dopants. Luminescence decay measurements showed a short lifetime of Ln3+ 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”.

Sensitization of nanoparticles (NPs) by appropriate lanthanide ions is crucial for the obtained spectroscopic properties. Nd3+ ions can absorb light at around 808 nm, allowing for deep tissue imaging, Yb3+ ions can be effectively excited by 975 nm radiation which is utilized in many areas, e.g. in anti-counterfeit applications, while Er3+ ions are capable of absorption around 1532 nm, which in turn, is important for solar energy conversion. Here, we describe a method for Nd3+ and Er3+ ions isolation in NPs by the synthesis of core/shell structures. As an alternative to the most commonly used core/shell thermal decomposition synthesis procedures, our products were obtained in water by a hydrothermal method. SrF2:Yb3+,Er3+@SrF2:Yb3+,Nd3+ NPs with sizes between 30 and 60 nm showed intense green to yellowish-red luminescence in the visible range, due to Er3+-doping. Yb3+ played the role of bridging ions, transferring energy absorbed by Nd3+ ions between the shell and core phases, limiting, in the same way, cross-relaxation between Nd3+ sensitizer ions and Er3+ luminescence centers. Structure, morphology and spectroscopic properties were investigated, revealing interesting processes taking place in the prepared NPs.

Nanomaterials based on BaREF 5 fluorides (where RE = Y, Gd and Lu), doped with lanthanide ions Yb 3+ /Ln 3+ (Ln 3+ = Er, Ho or Tm) were synthesized by microwave assisted hydrothermal method. The method of synthesis, structural and morphological properties are reported and discussed. The products obtained showed visible upconversion luminescence excited by the laser light of wavelength of 975 nm as a consequence of energy transfer between Yb 3+ and remaining Ln 3+ dopant ions. Their spectroscopic properties were characterized on the basis of excitation and emission spectra. Also luminescence decays and emission power dependences are presented and analysed. The materials compared revealed differences in their structural properties, reflected in their spectroscopic characteristics. The most intense luminescence was recorded for BaLuF 5 based materials which exhibited upconversion also as water colloids.

Synthesis and luminescence properties of yttrium oxyfluorides doped with Eu 3+ ions are reported. Modified sol–gel Pechini’s method has been used in order to obtain nanocrystalline YOF:Eu 3+ . X-ray diffraction analysis as well as Rietveld method of crystal structure refinement were used to confirm successful synthesis of single phase products. Eu 3+ influence on structure and morphology of YOF matrix has been studied with help of Scherrer equation and transmission electron microscopy. Emission and excitation spectra measurements were performed showing characteristic, spectroscopic properties of Eu 3+ ions. Emission decay curves showed a short rise of luminescence being confirmation of energy migration between Eu 3+ ions. Calculated luminescence lifetimes and integrated emission intensities were used to further investigation of samples and estimation of Judd–Ofelt intensity parameters.