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Europium doped (0.1% and 1%) chloroborate BaO–B 2 O 3 –BaCl 2 glass and glass-ceramic with embedded BaCl 2 nanocrystals have been synthesised, investigated, and compared with the corresponding nanocrystalline powder. The structural analysis of the glass evidenced ionic bonds characteristic to the glass host structure and compositional changes during the melting. X-ray diffraction and transmission electron microscopy revealed the formation of orthorhombic BaCl 2 nanocrystals of about tens on nm in size and a smaller amount of BaB 2 O 4 nanocrystals. Structural analysis of the Eu2+-doped BaCl 2 nanocrystals has shown a distortion of the crystalline cell assigned to the growth process, affected by defects and ionic impurities. Photoluminescence spectra of the glass-ceramic revealed Eu3+ and Eu2+ luminescent ion species, but only Eu2+ is incorporated within the BaCl 2 nanocrystalline phase. Electron paramagnetic resonance measurements in X-band sustain the presence of Eu2+ ions. The EPR parameters (g values and hyperfine constants) resulting from the Q-band EPR spectra simulations recorded on glass-ceramic are similar to those in Eu2+-doped BaCl 2 and confirmed the partial incorporation of Eu2+ ions within the BaCl 2 :Eu2+ nanocrystals in the glass-ceramics. [ABSTRACT FROM AUTHOR]

Highlights • Films of Ce 0.95 Yb 0.04 Er 0.01 O 2 , were grown by PLD on a single crystal silicon diode. • The up-conversion film grown for 2.3 J/cm2 delivers the highest device performance. • The relative power conversion efficiency of the device is 12.1/39.2% at 1/2.1 sun. • The external quantum efficiency is 7.2% when illuminated with 980 nm light. Abstract Co-doped CeO 2 thin films were grown from a bulk target with starting composition Ce 0.95 Yb 0.04 Er 0.01 O 2 by pulsed laser deposition (PLD) on a p+-n-n+ single crystal silicon diode. The PLD laser fluence was varied between 1.7 J/cm2 and 3.7 J/cm2. The device with the film grown for a laser fluence of 2.3 J/cm2 delivers the highest performance taking advantage of the up conversion (UC) effect provided by this film. Namely, the increase in the relative power conversion efficiency of the device is 12.1% and 39.2% for illumination under 1 and 2.1 sun, respectively, and its relative external quantum efficiency is 8.2% when illuminated with 980 nm light. The film grown for the optimum 2.3 J/cm2 fluence shows good target-film composition transfer and a granular morphology with a low roughness. The UC mechanism consists of efficient energy transfer between spatially separated Yb3+ and Er3+ ions, i.e. the absorption of infrared light photons by the Yb3+ ions (2 F 7/2 → 2 F 5/2 transition) is followed by a two-step energy transfer process to neighboring Er3+ ions and by their characteristic luminescent emissions ((2 H 11/2 , 4 S 3/2) → 4 I 15/2) and (4 F 9/2 → 4 I 15/2). [ABSTRACT FROM AUTHOR]

Complex physico-chemical investigations have been performed on white inlaid substance used in the ornamentation of prehistoric clay artefacts from southern Romania ceramics from the Early Chalcolithic, up to the Middle/Late Bronze Age. Structural and morphological investigations of the white pigments have showed hundreds of nm up to microns size particles with calcite and hydroxyapatite (ash bone) as dominant components. The calcite was found on Early Chalcolithic pigment vessels while those where hydroxyapatite was dominant from the Middle/Late Bronze Age. FTIR spectra revealed the biogenic source of the hydroxyapatite (i.e. cremated animal bone) and the crystallinity degree values agrees with the expected temperatures of firing of the ancient furnaces; the calcite-based pigments were supposed to be filled post firing. The EPR was not able to able to provide a clear assignment of the cremated animal bones but thermoluminescence showed various sources of calcite. [Display omitted] • Incised decoration pottery (Chalcolithic to the Bronze Age) from the southern Romania were studied. • For the pigment characterization we used complex physico-chemical investigations. • The mineralogical composition of the white pigment reflected a chronological differentiation. • The calcite was the main constituent of the pigment on the Chalcolithic pottery. • The predominant ingredient used in the Middle Bronze Age was hydroxyapatite from animal bone ash. [ABSTRACT FROM AUTHOR]

We present a comparative study between the properties of Yb 3 + /Er 3 + co-doped LiYF 4 thin films obtained by pulsed laser deposition (PLD) and matrix-assisted pulsed evaporation (MAPLE) growth techniques, respectively. We performed structural, morphological, and optical analyses in order to draw a conclusion about the potential of MAPLE as a growth technique used for the obtaining of RE-doped fluoride thin films having up-conversion properties. For both techniques the surface morphology is typical for laser processed thin films of RE-doped fluorides, with roughness values of the order of few hundreds of nanometers and a higher density of defects in the sample obtained by MAPLE. Up-conversion properties do not exhibit major differences between the thin film samples and the pressed target. Under 980 nm laser light pumping, both Yb 3 + /Er 3 + co-doped LiYF 4 thin film samples, obtained by PLD and MAPLE, show green (( 2 H 11/2 , 4 S 3/2 ) → 4 I 15/2 ) and red ( 4 F 9/2 → 4 I 15/2 ) up-conversion luminescence explained by a two-photon processes. Therefore MAPLE is a viable growth technique for the fundamental study of RE-doped fluoride thin films and their respective functional properties. [ABSTRACT FROM AUTHOR]

A novel glassy nanocomposite containing Er 3+ -doped BaCl 2 nanocrystals of about tens of nm embedded in a silicate matrix has been prepared by using sol-gel route followed by controlled crystallization of the xerogel. Under 810 nm laser light pumping it shows green (( 2 H 11/2 , 4 S 3/2 ) → 4 I 15/2 ) and red ( 4 F 9/2 → 4 I 15/2 ) up-conversion luminescences ascribed by a two-photon processes. The luminescence signal recorded in the oxychloride nano-glass ceramic is only about 10% compared to the NaYF 4 :Er 3+ (18%). In the nano-glass ceramic there are effective non-radiative decay channels, most probably related to hydroxyl ions and surface defects acting as centers for the non-radiatively energy dissipation. [ABSTRACT FROM AUTHOR]

Glassy nanocomposites containing Eu 3+ -doped LaOCl nanocrystals of about tens of nm size embedded in a silica matrix have been prepared by using sol–gel route followed by controlled crystallization of the xerogel. Crystallization behavior of LaOCl nanocristalline phase was discussed on the basis of thermal analysis, X-ray diffraction and photoluminescence measurements. LaOCl nanocrystalline phase precipitation is the result of lanthanum chloride hydrolytic and oxidative reactions. As the annealing temperature increases nanocrystallites size grows up to tens of nm; Eu 3+ -ions are gradually incorporated during the nanocrystals growth. Structural changes were studied using the Eu 3+ as probe ion and the luminescence properties were analysed by using Judd–Ofelt theory. [ABSTRACT FROM AUTHOR]

Abstract: Sol–gel chemistry within the pores of a polycarbonate template membrane was used for the preparation of Eosin Y–SiO2 hybrid nano- and microrods, using tetraethylorthosilicate [TEOS, Si(OC2H5)4] as the precursor in the presence of trifluoroacetic acid (TFA) catalyst. The ethanolic solution of Eosin-Y was added to the silica sol to trap dye molecules inside the SiO2 gel network during the gelation. Structural and morphological characterization using scanning electron microscopy (SEM) and luminescence microscopy have shown the formation of rods with 200nm and 1.2μm diameter and about 30μm length, exhibiting luminescence properties. Spectroscopic characterization has shown that the luminescence is due to Eosin-Y molecule in the xerogel porous network, surrounded by a solvation shell given mainly by the water. [Copyright &y& Elsevier]

Abstract: Glass–ceramics containing Eu3+-doped CaF2 nanocrystals of about 16nm size have been made using the controlled crystallization at higher temperatures of the Eu3+-doped CaF2–SiO2 xerogels. In the glass–ceramic material the Eu3+ ions are embedded in both silica network and in the non-centrosymmetric sites of the CaF2 nanocrystals structure. Lower phonon energy of CaF2 and the dehydratation processes reduce the probability of non-radiative de-excitations and as a result a luminescence enhancement and an increase of the PL lifetime is observed. Eu-doping modifies the traps distribution within the glass–ceramics and as a result an additional broad thermoluminescence peak at about 380°C was observed. The peak was assigned to the recombination of the electrons thermal released from the Eu3+-related traps in the glass matrix and in the CaF2 nanocrystals. [ABSTRACT FROM AUTHOR]

Abstract: Oxyfluoride glass samples in the system SiO2–Al2O3–CaF2–SmF3 were produced by using the melt-quenched technique and the kinetics of non-isothermal crystallization of CaF2 nano-crystals has been investigated. Differential thermal analysis (DTA) has shown an exothermic peak at about 700°C which was assigned to the CaF2 nano-crystals precipitation within the glass matrix as was identified by X-ray diffraction (XRD) analysis of the annealed glass samples. It was shown the Ozawa model is most suitable for describing the behaviour of non-isothermal crystallization of CaF2 nano-crystals within the glass matrix. The mean value of the Avrami exponent was found 1.16 which indicates the diffusion-controlled growth process of nano-particles in the glass system with zero nucleation rate as the single operative mechanism; the activation energy of the crystallization is Ed =379±25kJ/mol (3.93±0.26eV). The activation energy of the nano-crystals growth was computed within the same model and agrees very well with the activation energy of the crystallization. [ABSTRACT FROM AUTHOR]

Abstract: Transparent oxyfluoride glass-ceramic in the system SiO2–Al2O3–CaF2–EuF2 containing Eu-doped CaF2 nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF2 nanocrystals of about 65nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu3+ ion along with annealing time which is consistent with the Eu3+ environment evolving from a glassy to a crystalline state. [Copyright &y& Elsevier]

Abstract: The influence of Pb2+ doping on the optical properties of LiF crystals before and after irradiation with X-ray was studied by using optical absorption and photoluminescence measurements. After irradiation it was observed an increase of the absorption due to primary and aggregate electronic defects together with a higher photoluminescence signals associated with the F2 and F3 + colour centres in doped samples compared with the undoped ones. [Copyright &y& Elsevier]

Abstract: Thermoluminescence (TL) curve recorded after gamma-irradiation at room temperature of -doped phosphor shows TL peaks at 91, 147, 200, 235 and . The peak was tentatively attributed to the F centres recombination with hole centres trapped in the neighbourhood of the impurity. This peak shows a good stability (low fading) and has been used to characterise the TL phosphor dosimetric properties. TL dose dependence has shown a good linearity in the range from 0.2 to 10mGy, which makes it suitable for personal and medical dosimetry. The TL curves recorded after gamma rays or particles irradiation are similar, which suggests the possibility to use the phosphor also for particle detection. [Copyright &y& Elsevier]

We report on a photostimulated luminescence (PSL) effect in Ce-doped fluorobromozirconate glasses. Small hexagonal or orthorhombic BaBr2 crystallites are formed in the glass upon annealing. The PSL shows a (381,415) nm doublet which is due to the 5d–4f luminescence of Ce3+ in the orthorhombic BaBr2 crystallites embedded in the glass matrix. The stimulation band of the PSL peaking at 580 nm is probably due to perturbed F centres in the crystallites. After X-irradiation the magnetic circular dichroism of the optical absorption showed a broad band in the spectral range between 440 and 800 nm, having a derivative-like line shape centred at about 600 nm. The spectrum consists of two overlapping bands: one, derivative-like, belongs probably to F-centres, whereas the second band, superimposed on the low-energy region of the F-centre band, is due to a hole centre. [Copyright &y& Elsevier]

We found a significant PSL effect in Eu2+-doped fluorozirconate glasses (ZBLAN) which were additionally doped with Br- or Cl- ions. The PSL is attributed to the characteristic emission of Eu2+ present in nano-crystallites of BaBr2 or BaCl2, which form in the glass upon annealing. The metastable hexagonal form of BaX2 (X=Br,Cl) is always formed first before it is converted into the stable orthorhombic form. The particle size increases upon annealing and so does the PSL efficiency of the glass ceramic. However, there is a saturation of the PSL efficiency, which is for Br- doping about 9% and for Cl--doping about 80% of the Eu-doped BaFBr standard. The particle size was determined by transmission electron microscopy (TEM). The TEM results show a clear tendency for bigger particles for longer annealing at the expense of its number. The particle size for the most efficient phosphor is about 100 nm. [Copyright &y& Elsevier]

In orthorhombic BaBr2 : Ce3+ two kinds of luminescence bands at room temperature have been attributed to charge-compensated Ce3+ centres. One type was associated with potassium (or some other monovalent cation) on a neighbouring Ba site and another one associated with an unidentified defect. A third kind of emission, observed only as low temperature photoluminescence (PL), is ascribed to isolated Ce3+ ions. The charge-compensated Ce3+ complexes are active both in PL and photostimulated luminescence (PSL) following X-ray irradiation. The PSL is nearly as efficient as in the case of the commercially used X-ray storage phosphor BaFBr:Eu2+. The X-ray induced electrons are trapped in F-type centres whose band position is characteristic for the nearby Ce complex. As shown by the fingerprint character of the PSL itself, the hole partner in the recombination is also associated or identical with the same Ce complex. [Copyright &y& Elsevier]

Abstract: Bi4(GeO4)3 glass materials have been characterized by X-ray excited luminescence, photoluminescence and cathodo-luminescence measurements. The materials were obtained by crystallization at different temperatures and their spectroscopic parameters were compared before and after crystallization. Thermoluminescence curves recorded after electron irradiation of BGO glass behave similarly to BGO crystals, showing several peaks between 408K (135°C) and 610K (337°C). The differences between the Bi4(GeO4)3 crystals and glass materials are believed to result from the random distribution of GeO4 tetrahedra around Bi3+ ions which influences the photoluminescence and TL parameters. The CL images of glass-ceramic samples obtained by partial crystallization at 600°C show luminescent crystalline structures, which are probably responsible for the increase in scintillation efficiency. [Copyright &y& Elsevier]

The crystallization process of Yb 3+ /Er 3+ codoped LiYF 4 nanoparticles obtained by sol-gel method was studied using differential scanning calorimetry and X-ray diffraction. Thermal data obtained from differential scanning calorimetry measurements under non-isothermal conditions at different heating rates were examined using both model-free and model fitting approaches. It was shown that LiYF 4 phase crystallization occurs at around 383 °C as a result of the thermal decomposition of trifluoracetates and is shifted to higher temperatures as the heating rate increases. Both Friedman and Ozawa-Flynn-Wall analyses have indicated that the activation energy and pre-exponential factor decrease slightly as the crystallization proceeds. According to the model-fitting approach (by using extended Prout-Tompkins nth-order, ath autocatalysis reaction), LiYF 4 nanocrystalline phase is the result of an autocatalytic process where a second metastable phase YF 3 acts as a catalyst that accelerates the crystallization process of the LiYF 4 phase. [ABSTRACT FROM AUTHOR]