Anna M. Kaczmarek

Enhanced Luminescence in Ln3+-Doped Y2WO6 (Sm, Eu, Dy) 3D Microstructures through Gd3+ Codoping

Microstructures of Y2WO6 were prepared by applying a hydrothermal synthesis in the presence of sodium dodecyl sulfate (SDS) surfactant, after which the materials were heat-treated at a temperature of 1100 °C. When prepared at pH 3, the spherical 3D microstructures were built from nanosized particles. Raising the pH gave materials built from differently shaped building blocks, which influenced the final architecture. These materials, similarly to other previously investigated and reported rare-earth tungstate materials, were found to show very interesting luminescence properties. However, quantum yield (QY) values have scarcely been reported for such materials. In this work, a detailed study of the photoluminescence characteristics, decay times, and quantum yields of Y2WO6 doped with Sm(3+), Eu(3+), and Dy(3+) is presented. When doped with different concentrations of Ln(3+) ions, the luminescence properties of the samples changed. The 2.5% Dy:Y2WO6 sample gave white-light emission and showed a QY of 17%. For the optimal lanthanide-ion concentrations, the systems were codoped with 2% and 10% Gd(3+) ions to test the possible enhancement of luminescence through energy transfer from W-O and/or Gd(3+) to Ln(3+). The Eu(3+),Gd(3+)-codoped system showed QYs as high as 79%. The Sm,Gd-codoped system showed the highest enhancement of QY. After incorporation of Gd(3+) ions, the 2.5% Sm_10% Gd:Y2WO6 materials showed a QY approximately 2.4 times larger than that of the 2.5% Sm:Y 2WO6 material.

Dopant and excitation wavelength dependent color-tunable white light-emitting Ln3+:Y2WO6 materials (Ln3+ = Sm, Eu, Tb, Dy)

Microstructured Y2WO6 materials were prepared in a hydrothermal synthesis in the presence of glycerol, which was employed as both a solvent and a structure directing agent, after which they were heat treated at 1100 °C. These materials, similar to other previously reported Y2WO6 as well as other rare-earth tungstate structures, showed interesting luminescence properties. Six Ln(3+) doped or co-doped samples, which showed white light emission, are described in this paper. It was observed that the doping ion(s)/doping percentage, heat treatment of the material, as well as the chosen excitation wavelength could be used to tune the emission color of the samples to obtain white light with a warmer or colder undertone. The luminescence lifetimes, quantum yields, CIE coordinates and correlated color temperatures for these samples were determined. Additionally, for the co-doped Y2WO6 samples the energy transfer mechanisms were proposed because a significant change in the luminescence properties was observed after heat treatment. This can be linked to the conversion from distorted tungstate groups in the precursor material to regular tungstate groups in the heat treated material.

Tuning the architecture and properties of microstructured yttrium tungstate oxide hydroxide and lanthanum tungstate

In this paper, various microstructures of yttrium and lanthanum tungstates were synthesized under hydrothermal conditions, at pH 5, in a ligand-free environment, and in the presence of a dioctyl sodium sulfosuccinate (DSS) surfactant. It was observed that the shape of the nanobuilding blocks, and therefore the architecture of the microstructures, could be tuned by controlling the reaction conditions, such as the source of the rare earth, the amount of a surfactant and the reaction time. X-ray powder diffraction (XRD), elemental analysis, scanning electron microscopy (SEM), and N2 adsorption were employed to characterize the obtained products. The photoluminescent properties of Eu(3+) and Dy(3+) doped tungstate materials were investigated. Luminescence measurements showed an efficient charge transfer from the WO4(2-) groups to Eu(3+) and Dy(3+) ions. It was found that under UV excitation the Dy(3+) doped Y(WO3)2(OH)3 and La2(WO4)3 precursors exhibit white emission.

Lanthanide 9-anthracenate: solution processable emitters for efficient purely NIR emitting host-free OLEDs

Searching for new NIR emitting materials, lanthanide 9-anthracenates Ln(ant)3 were synthesized and thoroughly characterized. Ytterbium 9-anthracenate Yb(ant)3, that demonstrated the highest NIR luminescence efficiency, was successfully used as an emission layer of a host-free OLED and its electroluminescence quantum efficiency, corresponding to the sole band at 1000 nm, reached 0.21%. This performance could be achieved due to the high quantum yield of Yb(ant)3, which reached 1.5% and was increased up to 2.5% by partial Yb3+ substitution with Lu3+, as well as its high electron mobility due to the extended stacking in its crystal structure. The first gadolinium-based PHOLED was prepared based on Gd(ant)3.

Influence of Y3+, Gd3+, and Lu3+ co-doping on the phase and luminescence properties of monoclinic Eu:LaVO4 particles

Nano-sized particles of monoclinic-LaVO4 were prepared in a short reaction time of 30 minutes by employing a microwave assisted hydrothermal synthesis in the presence of glycerol, which was used both as a solvent and structure-directing agent. The tetragonal-LaVO4 is known to show strong luminescence properties when doped with Ln(3+), whereas the monoclinic-LaVO4 is usually considered not suitable for luminescence and therefore luminescence properties of monoclinic-LaVO4 doped with Ln(3+) ions are seldom investigated. Due to the scarce amount of research on the topic of luminescence of Ln(3+) doped monoclinic-LaVO4 in this paper a detailed study of solid state luminescence properties, including quantum yields, of nano-sized monoclinic-LaVO4 doped with different molar percentages of Eu(3+) is presented. It was observed that the 12.5%Eu(3+) doped sample showed the strongest luminescence properties. Additionally a study of the influence of different rare-earth ions (Y(3+), Gd(3+), Lu(3+)) co-doped into the particles was performed in order to explore the potential of increasing the luminescence of these materials. Furthermore stable colloidal suspensions of the Eu(3+) doped monoclinic-LaVO4 nanoparticles showing strong red emission could be obtained.

Mechanochemically synthesized crystalline luminescent 2D coordination polymers of La3+ and Ce3+, doped with Sm3+, Eu3+, Tb3+, and Dy3+: synthesis, crystal structures and luminescence

The luminescence properties of two series of heteronuclear lanthanide-based coordination polymers were studied. The heteronuclear compounds were synthesized via mechanosynthesis routes. These series have the general chemical formula [Ln1−xLn′x(pzdc)(Hpzdc)(H2O)3]n (Ln = La3+ or Ce3+, Ln′ = Sm3+, Eu3+, Tb3+, or Dy3+, x = 0.050, 0.075 or 0.100) where H2pzdc stands for 2,3-pyrazinedicarboxylic acid (Hpzdc− = mono-deprotonated and pzdc2− = bis-deprotonated). The heteronuclear compounds that belong to each series are isostructural to a new two-dimensional La(III) coordination polymer and to an already reported homonuclear two-dimensional Ce(III) coordination polymer, [La(pzdc)(Hpzdc)(H2O)3]n and [Ce(pzdc)(Hpzdc)(H2O)3]n, respectively. These two crystal structures are isostructural as well. The La(III) and Ce(III) compounds have been synthesized via conventional heating and mechanosynthesis. The La(III) coordination polymer was structurally characterized by single crystal X-ray diffraction and was shown to consist of 2D sheets that construct a three-dimensional supramolecular architecture via non-covalent interactions i.e. hydrogen bonding. To find the optimal lanthanide-ion concentrations, the systems were doped with 5%, 7.5% or 10% of a spectroscopically active ion (Sm3+, Eu3+, Tb3+, or Dy3+) to investigate the luminescence properties.

Optical thermometry of MoS2:Eu3+ 2D luminescent nanosheets

Here, we report the incorporation of Eu3+ ions into a MoS2 2D material through a two-step bottom-up hydrothermal approach. Temperature dependent measurements in the 60–360 K range were carried out to determine the optical thermometric properties of the material. This material could offer a new strategy to exploit temperature sensors and heaters.

Eu3+@PMO: synthesis, characterization and luminescence properties

A periodic mesoporous organosilica (PMO) functionalized with dipyridyl-dihydropyridazine units has been successfully prepared by a hetero Diels–Alder reaction between the double bonds of an ethenylene-bridged PMO material and a substituted tetrazine. The ordering and mesoporosity of the parent material is maintained after the post-modification process, and the surface Diels–Alder adducts are clearly observable in the pores. These dipyridyl-dihydropyridazine moieties can form interesting chelates with lanthanide ions. Thus, two novel organic–inorganic luminescent hybrid materials have been obtained by linking of Eu3+ compounds to an ethene-PMO functionalized with dipyridyl-dihydropyridazine. Both materials have been studied in depth by photoluminescence spectroscopy and luminescence decay time measurements. Our results reveal the key role of surface Diels–Alder adducts as suitable sensitizing ligands for europium ions.

Controlled fluorescence in a beetle’s photonic structure and its sensitivity to environmentally induced changes

The scales covering the elytra of the male Hoplia coerulea beetle contain fluorophores embedded within a porous photonic structure. The photonic structure controls both insect colour (reflected light) and fluorescence emission. Herein, the effects of water-induced changes on the fluorescence emission from the beetle were investigated. The fluorescence emission peak wavelength was observed to blue-shift on water immersion of the elytra whereas its reflectance peak wavelength was observed to red-shift. Time-resolved fluorescence measurements, together with optical simulations, confirmed that the radiative emission is controlled by a naturally engineered photonic bandgap while the elytra are in the dry state, whereas non-radiative relaxation pathways dominate the emission response of wet elytra.

Low-Percentage Ln3+ Doping in a Tetranuclear Lanthanum Polyoxometalate Assembled from [Mo7O24]6– Polyanions Yielding Visible and Near-Infrared Luminescence

A rare case of low-percentage trivalent lanthanide doping in multinuclear lanthanide polyoxometalates (LnPOMs) was investigated. The [La4(MoO4)(H2O)16(Mo7O24)4]14- polyanion was chosen as the host material for this study. In this polyanion the central [La4(MoO4)]10+ core is coordinated by four heptamolybdate groups as well as 16 water molecules. The tetranuclear lanthanum POM was doped with 5% of Eu3+, Tb3+, Sm3+, Dy3+, Nd3+, Er3+, and Yb3+ (according to synthesis), and the structures and luminescence properties of the x%Ln:LaPOMs were investigated. Additionally a series of tetranuclear lanthanide POMs built from [Mo7O24]6- heptamolybdate polyanions with Eu3+, Tb3+, Sm3+, Dy3+, and Nd3+ instead of La3+ were synthesized, and a detailed analysis revealed that the tetranuclear clusters formed monomers or dimers linked through oxygen bridges. The smaller lanthanide ions, namely, Er3+ and Yb3+, did not form tetranuclear clusters, but instead mononuclear sandwich-type POMs were obtained. The obtained structures were shown to be lanthanide-specific, and not a result of different synthetic/crystallization conditions. The luminescence properties of the x%Ln:LaPOMs were compared with the luminescence properties of the LnPOMs.