Red- and green-emitting nano-clay materials doped with Eu3+ and/or Tb3.

Trivalent europium (Eu3+ ) and terbium (Tb3+ ) ions are important activator centers used in different host lattices to produce red and green emitting materials. The current work shows the design of new clay minerals to act as host lattices for rare earth (RE) ions. Based on the hectorite structure, nano-chlorohectorites and nano-fluorohectorites were developed by replacing the OH- present in the hectorite structure with Cl- or F- , thus avoiding the luminescence quenching expected due to the OH- groups. The produced matrices were characterized through X-ray powder diffraction (XPD), transmission electron microscopy (TEM), FT-IR, 29 Si MAS (magic angle spinning) NMR, nitrogen sorption, thermogravimetry-differential scanning calorimetry (TGA-DSC) and luminescence measurements, indicating all good features expected from a host lattice for RE ions. The nano-clay materials were successfully doped with Eu3+ and/or Tb3+ to yield materials preserving the hectorite crystal structure and showing the related luminescence emissions. Thus, the present work shows that efficient RE3+ luminescence can be obtained from clays without the use of organic 'antenna' molecules.

Rapid and Energy-Saving Microwave-Assisted Solid-State Synthesis of Pr(3+)-, Eu(3+)-, or Tb(3+)-Doped Lu2O3 Persistent Luminescence Materials.

Persistent luminescence materials Lu2O3:R(3+),M (Pr,Hf(IV); Eu; or Tb,Ca(2+)) were successfully and rapidly (22 min) prepared by microwave-assisted solid-state synthesis (MASS) using a carbon microwave susceptor and H3BO3 as flux. Reaction times are reduced by up to 93% over previous synthetic methods, without special gases application and using a domestic microwave oven. All materials prepared with H3BO3 flux exhibit LuBO3 impurities that were quantified by Rietveld refinement from synchrotron radiation X-ray powder diffraction patterns. The flux does not considerably affect the crystalline structure of the C-Lu2O3, however. Scanning electron micrographs suggest low surface area when H3BO3 flux is used in the materials' synthesis, decreasing the amount of surface hydroxyl groups in Lu2O3 and improving the luminescence intensity of the phosphors. The carbon used as the susceptor generates CO gas, leading to complete reduction of Tb(IV) to Tb(3+) and partial conversion of Pr(IV) to Pr(3+) present in the Tb4O7 and Pr6O11 precursors, as indicated by X-ray absorption near-edge structure data. Persistent luminescence spectra of the materials show the red/near-IR, reddish orange, and green emission colors assigned to the 4f(n) → 4f(n) transitions characteristics of Pr(3+), Eu(3+), and Tb(3+) ions, respectively. Differences between the UV-excited and persistent luminescence spectra can be explained by the preferential persistent luminescence emission of R(3+) ion in the S6 site rather than R(3+) in the C2 site. In addition, inclusion of Hf(IV) and Ca(2+) codopants in the Lu2O3 host increases the emission intensity and duration of persistent luminescence due to generation of traps caused by charge compensation in the lattice. Photonic materials prepared by MASS with H3BO3 flux show higher persistent luminescence performance than those prepared by the ceramic method or MASS without flux. Color tuning of persistent luminescence in Lu2O3:R(3+),M provides potential applications in bioimaging as well as in solar cell sensitizers.

Optically stimulated persistent luminescence of europium-doped LaAlO3 nanocrystals.

Optically stimulated persistent luminescence was investigated for europium-doped LaAlO3 nanocrystals. This system shows conventional luminescence of both the Eu(3+) line emission and the weak broad-band emission of Eu(2+) upon UV excitation. The persistent luminescence is predominantly associated with the Eu(3+) emission, and can be amplified significantly through irradiation with IR at 975 nm. The conventional luminescence from Eu(3+) is strongly enhanced when the material is excited simultaneously with both UV and IR radiation. The enhancement of persistent luminescence is accompanied by increased persistent photoconductivity. The charge transfer band of the LaAlO3:Eu(3+) nanocrystals in the UV excitation spectra significantly weakens with increasing IR excitation power, also correlating well with the enhancement of persistent luminescence. Finally, a mechanism is presented for the optically stimulated and persistent luminescence in this Eu(2+)- and Eu(3+)-doped LaAlO3 material.

Red-green emitting and superparamagnetic nanomarkers containing Fe3O4 functionalized with calixarene and rare earth complexes.

The design of bifunctional magnetic luminescent nanomaterials containing Fe3O4 functionalized with rare earth ion complexes of calixarene and ß-diketonate ligands is reported. Their preparation is accessible through a facile one-pot method. These novel Fe3O4@calix-Eu(TTA) (TTA = thenoyltrifluoroacetonate) and Fe3O4@calix-Tb(ACAC) (ACAC = acetylacetonate) magnetic luminescent nanomaterials show interesting superparamagnetic and photonic properties. The magnetic properties (M-H and ZFC/FC measurements) at temperatures of 5 and 300 K were explored to investigate the extent of coating and the crystallinity effect on the saturation magnetization values and blocking temperatures. Even though magnetite is a strong luminescence quencher, the coating of the Fe3O4 nanoparticles with synthetically functionalized rare earth complexes has overcome this difficulty. The intramolecular energy transfer from the T1 excited triplet states of TTA and ACAC ligands to the emitting levels of Eu(3+) and Tb(3+) in the nanomaterials and emission efficiencies are presented and discussed, as well as the structural conclusions from the values of the 4f-4f intensity parameters in the case of the Eu(3+) ion. These novel nanomaterials may act as the emitting layer for the red and green light for magnetic light-converting molecular devices (MLCMDs).

Oligonucleotide array-in-well platform for detection and genotyping human adenoviruses by utilizing upconverting phosphor label technology.

We have developed a robust array-in-well test platform based on an oligonucleotide array, combining advantages of simple instrumentation and new upconverting phosphor reporter technology. Upconverting inorganic lanthanide phosphors have a unique property of photoluminescence emission at visible wavelengths under near-infrared excitation. No autofluorescence is produced from the sample or support material, enabling a highly sensitive assay. In this study, the assay is performed in standard 96-well microtiter plates, making the technique easily adaptable to high-throughput analysis. The oligonucleotide array-in-well assay is employed to detect a selection of ten common adenovirus genotypes causing human infections. The study provides a demonstration of the advantages and potential of the upconverting phosphor-based reporter technology in multianalyte assays and anti-Stokes photoluminescence detection with an anti-Stokes photoluminescence imaging device.

Up-conversion luminescence of the NaRF4-NaR'F4 (R: Y, Yb, Er) core-shell nanomaterials.

Up-converting NaRF(4)-NaR'F(4) (R: Y, Yb, Er) nanomaterials with different core-shell combinations were prepared with the co-precipitation method. The X-ray powder diffraction (XPD) measurements revealed the presence of both the cubic and hexagonal NaRF(4) phases. The crystallite sizes calculated with the Scherrer formula were 100 and 150 nm for the cubic and hexagonal phases, respectively. The FT-IR spectra showed water impurities. The up-conversion luminescence and luminescence decays were studied with NIR laser excitation at 970 nm. The up-conversion luminescence spectra showed strong red (640-685 nm) ((4)F(9/2) → (4)I(15/2)) and moderate green (515-560 nm) ((2)H(11/2,) (4)S(3/2) → (4)I(15/2)) Er(3+) luminescence. The strongest up-conversion luminescence and longest red luminescence decay was obtained from the Na(Y,Yb)F(4)-NaErF(4) core-shell combination.

Preparation and characterization of nanocrystalline ZrO2:Yb3+,Er3+ up-conversion phosphors.

Nanocrystalline up-converting phosphors with zirconium oxide (ZrO(2)) as the host lattice were prepared with combustion and sol-gel methods. Impurities were analyzed with Fourier transform infrared (FT-IR) spectroscopy. Yb(3+) absorption was studied in the wave number region 10,000-11,500 cm(-1) at room temperature and at 10 K. The whole-blood absorption was measured in the region 9100-41,600 cm(-1) at room temperature. Up-conversion luminescence was excited at room temperature with an IR-laser at 977 nm. The up-conversion luminescence spectra showed red (650-685 nm) and green emission (520-560 nm) due to the (4)F(9/2) --> (4)I(15/2) and ((2)H(11/2), (4)S(3/2)) --> (4)I(15/2) transitions of Er(3+), respectively. The materials prepared with combustion synthesis were found to yield the most efficient up-conversion intensity and the longest luminescence decay.

Defect structure and up-conversion luminescence properties of ZrO2:Yb3+,Er3+ nanomaterials.

The up-converting ZrO2:Yb3+,Er3+ nanomaterials were prepared with the combustion and sol-gel methods. FT-IR spectroscopy was used for analyzing the impurities. The crystal structures were characterized with X-ray powder diffraction and the mean crystallite sizes were estimated with the Scherrer formula. Up-conversion luminescence measurements were made at room temperature with IR-laser excitation at 977 nm. The IR spectra revealed the conventional NO3- and OH- impurities for the combustion synthesis products. The structure of the ZrO2:Yb3+, Er3+ nanomaterials was cubic except for the minor monoclinic and tetragonal impurities obtained with the sol-gel method. The materials showed red (650-700 nm) and green (520-560 nm) up-conversion luminescence due to the 4F9/2-->4I15/2 and (2H11/2, 4S3/2)-->4I15/2 transitions of Er3+, respectively. The products obtained with the combustion synthesis exhibited the most intense luminescence intensity and showed considerable afterglow.

Thermoluminescence study of persistent luminescence materials: Eu2+- and R3+-doped calcium aluminates, CaAl2O4:Eu2+,R3+.

Thermoluminescence properties of the Eu2+-, R3+-doped calcium aluminate materials, CaAl2O4:Eu2+,R3+, were studied above room temperature. The trap depths were estimated with the aid of the preheating and initial rise methods. The seemingly simple glow curve of CaAl2O4:Eu2+ peaking at ca. 80 degrees C was found to correspond to several traps. The Nd3+ and Tm3+ ions, which enhance most the intensity of the high-temperature TL peaks, form the most suitable traps for intense and long-lasting persistent luminescence, too. The location of the 4f and 5d ground levels of the R3+ and R2+ ions were deduced in relation to the band structure of CaAl2O4. No clear correlation was found between the trap depths and the R3+ or R2+ level locations. The traps may thus involve more complex mechanisms than the simple charge transfer to (or from) the R3+ ions. A new persistent luminescence mechanism presented is based on the photoionization of the electrons from Eu2+ to the conduction band followed by the electron trapping to an oxygen vacancy, which is aggregated with a calcium vacancy and a R3+ ion. The migration of the electron from one trap to another and also to the aggregated R3+ ion forming R2+ (or R3+-e-) is then occurring. The reverse process of a release of the electron from traps to Eu2+ will produce the persistent luminescence. The ability of the R3+ ions to trap electrons is probably based on the different reduction potentials and size of the R3+ ions. Hole trapping to a calcium vacancy and/or the R3+ ion may also occur. The mechanism presented can also explain why Na+, Sm3+, and Yb3+ suppress the persistent luminescence.