Investigation of Phase Separation in Doped and Un-doped Sodium Borosilicate Glasses

The practical importance of phase separation for the optical and mechanical properties of many glass forming systems is well established. In the present contribution glasses within the immiscibility region of the sodium borosilicate system as well as samples to which 0.5 and 1 Mol% dopant ions (Eu³⁺ and P⁵⁺) have been added, were prepared under normal conditions. The separation process is monitored by UV-Vis transmittance and luminescence spectroscopy. The spectra are recorded after different intervals of heat-treatment in air. From the transmittance spectra chromaticity coordinates are obtained and the effect of heat treatment is depicted in chromaticity diagrams. From the luminescence spectra of the Eu³⁺ doped samples asymmetry ratios are obtained

Strukturna i dielektrična svojstva nanostrukturnih prahova BaTiO3 punjenih ionima Eu3+ I pripremljenih sol-gel procesom

Nano-structure BaTiO3 powders doped with Eu3+ ions have been prepared by a sol-gel technique. X-ray diffraction (XRD) results indicate that BaTiO3 gel powders crystallize into tetragonal symmetry on heat treatment at 750 ◦C. Particle sizes as small as 3.5 nm were measured for pure BaTiO3 powders. The XRD data were confirmed by transmission electron microscope. Room-temperature luminescence spectra of BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ and BaTiO3:2% Eu3+ powders have been measured. The luminescence spectra of prepared ultrafine powders are dominated by the 5D0 →7F2 transition in Eu3+, suggesting a strong distortion of the Eu3+ sites. The foreign ions are mainly accommodated in Ba2+ tetragonal sites, which are then distorted by the occurrence of different ionic charge of the two cations Ba2+ and Eu3+. The dielectric constant, ε, of BaTiO3, BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ and BaTiO3:2% Eu3+ powders at frequency 100 Hz was found to be equal to 1000, 1211, 1455 and 1800, respectively. This high dielectric constant is believed to arise from the increase of the crystallite size, when increasing the concentration of Eu3+ ions. After annealing in argon at 400 ◦C for two hours, at 100 Hz, the dielectric constant of the pure sample was 625 and the AC resistivity also decreased. The room temperature (RT) AC resistivity of the samples depends on the concentration of Eu3+ ions in BaTiO3 powders, and was found to decrease as the concentration of Eu3+ ions increased.Pripremali smo sol-gel metodom nanostrukturne prahove BaTiO3 punjene Eu3+ ionima. Difrakcija X-zračenja (DXZ) pokazuje da se gel prahovi BaTiO3 kristaliziraju u tetragonalnoj simetriji zagrijavanjem na 750 ◦C. Utvrdili smo veličine zrna od samo 3.5 nm u čistom prahu BaTiO3. Podatke od DXZ potvrdili smo prolaznom elektronskom mikroskopijom. Mjerili smo fotoluminescentne spektre prahova BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ i BaTiO3:2% Eu3+ na sobnoj temperaturi. U luminescentnim spektrima pripremljenih ultrafinih prahova prevladava prijelaz 5D0 →7F2 u Eu3+, što ukazuje na snažna izobličenja na mjestima Eu3+ iona. Ugrađeni se ioni Eu3+ uglavnom smještaju na tetragonalne položaje Ba2+, a velika razlika ionskih naboja dvaju kationa, Ba2+ i Eu3+, uzrokuje snažne promjene oko tog defekta. Dielektrične konstante, ε, prahova BaTiO3, BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ i BaTiO3:2% Eu3+ na frekvenciji 100 Hz prema našim mjerenjima iznose 1000, 1211, 1455 odn. 1800. Smatramo da su tako velike vrijednosti dielektrične konstante posljedica povećanih veličina kristalita za veća punjenja ionima Eu3+. Nakon opuštanja u argonu na 400 ◦C tijekom dva sata, dielektrična konstanta čistog praha bila je 625, a otpornost se također smanjila. Izmjenična otpornost prahova BaTiO3 ovisi o punjenju ionima Eu3+ i nalazi se da se smanjuje kada se poveća sadržaj iona Eu3+

Temperature dependence and temporal dynamics of Mn2+ upconversion luminescence sensitized by Yb3+ in codoped LaMgAl11O19

A detailed spectroscopic study of the upconversion properties in Mn2+-Yb3+ codoped LaMgAl11O19 is presented. Pulsed and continuous-wave infrared excitation in the 2F7/2--2F5/2 Yb3+ absorption peaks induces broad Mn2+ green emission at 19450 cm-1, which is assigned to the 4T1--6A1 transition in tetrahedral Mn2+ and sharp peaks associated with Yb3+-pairs luminescence. Both emissions have very different temporal evolution and can be separated by time-resolved spectroscopy. Among the different concentrations under investigation, the 2%Mn2+-5%Yb3+ codoped system presents the highest upconversion efficiency. The corresponding emission remains visible to the naked eye up to 650 K. The time dependence of the Mn2+ luminescence upon Yb3+ excitation shows distinct behaviors for different doping concentrations. The temporal evolution of the intensity for the diluted system doped with 2%Mn2+ and 5%Yb3+ together with the pure manganese compound doped with 1%Yb3+, as well as the temperature dependence of the upconversion emission intensity and lifetime are relevant to identify the underlying upconversion mechanisms. We show that the main processes responsible for upconversion in this doubly transition-metal rare-earth doped oxide are both ground-state absorption (GSA)/excited-state absorption and GSA/energy-transfer upconversion. An analysis of these processes yielding highly efficient luminescence is discussed on the basis of crystal structure and dopants.This work was financially supported by the Spanish Ministerio de Ciencia e Innovación (Project No. MAT2008- 06873-C02-01/MAT) and the MALTA-Consolider Ingenio 2010 (Reference No. CSD2007-00045). R.M.-R. thanks the Spanish MEC for a FPI research grant (Reference No. BES-2006-13359)

Polarized micro-Raman spectroscopy and ab initio phonon modes calculations of LuPO4

The vibrational dynamics of lutetium orthophosphate (LuPO4) single crystals was carefully investigated by means of polarized micro-Raman spectroscopy and ab initio calculations. Eleven of the twelve independent components of the polarizability tensor, expected on the basis of the group theory for LuPO4, were selected in turn and assigned in symmetry. The only B1g(2) Raman mode was not observed, likewise due to either its very small intensity or its nearness in energy with forbidden Raman modes, which spill and could hide it. Both Raman and infrared vibrational modes are evaluated by densityfunctional theory calculations using effective core pseudo-potential. The agreement between calculated and experimental frequencies is very good. On the basis of our ab initio results, and of reduced-mass ratio considerations, the expected wavenumber of the missing B1g (2) mode falls close to that of Eg(3) mode peaked at about 306 cm1, and therefore we can definitively conclude that the observation of the missing B1g (2) mode is masked by the spill-over of this Eg mode

Assessing Single Upconverting Nanoparticle Luminescence by Optical Tweezers

We report on stable, long-term immobilization and localization of a single colloidal Er3+/Yb3+ codoped upconverting fluorescent nanoparticle (UCNP) by optical trapping with a single infrared laser beam. Contrary to expectations, the single UCNP emission differs from that generated by an assembly of UCNPs. The experimental data reveal that the differences can be explained in terms of modulations caused by radiation-trapping, a phenomenon not considered before but that this work reveals to be of great relevanceThis work was supported by the Spanish Ministerio de Educación y Ciencia (MAT2010–16161 and MAT2013–47395-C4–1-R). P.H.G. thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the Juan de la Cierva program. P.R.S thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the “Promoción 14 del talento y su Empleabilidad en I+D+i” statal program. Fondazione Cariverona (Verona, Italy) is gratefully acknowledged for financial support in the frame of the project “Verona Nanomedicine Initiative

Structural characterisation and luminescence properties of nanostructured lanthanide-doped Sc2O3 prepared by propellant synthesis

Nanocrystalline powders of undoped and lanthanide-doped scandium oxide were prepared by propellant synthesis and characterized by x-ray powder diffraction, electron microscopy, EDX spectroscopy and luminescence spectroscopy. The obtained material has the Sc2O3 cubic structure (space group ) with unit cell parameter increasing with the size of the dopant. The crystallite size is in the range 20-40 nm. The lanthanide-doped samples form Sc2-xLnxO3 solid solutions with x 480.2 (Ln = Eu or Er). No inhomogeneity was found by microanalysis on the micron scale. The emission spectrum of the Eu3+ doped Sc 2O3 sample shows strong bands in the visible region assigned to 4f-4f transitions of the lanthanide ion

Nanocrystalline lanthanide-doped Lu3Ga5O12 garnets: interesting materials for light-emitting devices

Nanocrystalline Lu3Ga5O12, with average particle sizes of 40 nm, doped with a wide variety of luminescent trivalent lanthanide ions have been prepared using a sol\u2013gel technique. The structural and morphological properties of the powders have been investigated by x-ray powder diffraction, high resolution transmission electron microscopy and Raman spectroscopy. Structural data have been refined and are presented for Pr3+, Eu3+, Gd3+, Ho3+, Er3+ and Tm3+ dopants, while room temperature excited luminescence spectra and emission decay curves of Eu3+-, Tm3+- and Ho3+-doped Lu3Ga5O12 nanocrystals have been measured and are discussed. The Eu3+ emission spectrum shows typical bands due to 5D0 \u21927FJ (J = 0, 1, 2, 3, 4) transitions and the broadening of these emission bands with the non-exponential behaviour of the decay curves indicates the presence of structural disorder around the lanthanide ions. Lanthanide-doped nanocrystalline Lu3Ga5O12 materials show better luminescence intensities compared to Y2O3, Gd3Ga5O12 and Y3Al5O12 nanocrystalline hosts. Moreover, the upconversion emission intensity in the blue-green region for the Tm3+- and Ho3+-doped samples shows a significant increase upon 647.5 nm excitation with respect to other common oxide hosts doped with the same lanthanide ions

Inverted Opal Luminescent Ce-Doped Silica Glasses

Inverted opal Ce-doped silica glasses (Ce : Si molar ratio 1 ⋅ 10−3 were prepared by a sol-gel method using opals of latex microspheres as templates. The rare earth is homogeneously dispersed in silica host matrix, as evidenced by the absence of segregated CeO2, instead present in monolithic Ce-doped SG with the same cerium content. This suggests that the nanometric dimensions of bridges and junctions of the host matrix in the inverted opal structures favor the RE distribution avoiding the possible segregation of CeO2

Structural and luminescence investigation on gadolinium gallium garnet nanocrystalline powders prepared by solution combustion synthesis

Nanocrystalline powders of undoped and lanthanide (Pr3+, Tm3+)- doped gadolinium gallium garnet, Gd3Ga5O12 (GGG), were prepared by propellant synthesis and studied by x-ray powder diffraction (XRD), electron diffraction (ED), high-resolution electron microscopy (HREM) and luminescence spectroscopy. The x-ray diffraction patterns of the GGG samples were analysed using the Rietveld method. The Rietveld refinement reveals the existence of two garnet-type phases: both are cubic (space group Ia $(3) over bar$d) with a slightly different lattice parameter and probably a slightly different composition. Electron diffraction and electron microscopy measurements confirm the x-ray diffraction results. EDX measurements for lanthanide-doped samples show that stable solid solutions with composition Gd(3-x)Ln(x)Ga(5)O(12), x approximate to 0.3 ( Ln = Pr; Tm) have been obtained. The luminescence properties of the Tm3+ -doped nanocrystalline GGG samples were measured and analysed