| 1. |
- Labrador Paez, Lucia, et al.
(author)
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Eu 3+luminescent ions detect water density anomaly
- 2020
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In: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 223
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Journal article (peer-reviewed)abstract
- It is well known that water density varies anomalously with temperature. However, nowadays there is still a lack of agreement on the causes of this phenomenon. In this work, we use Eu3+ luminescent ion as a probe to investigate the changes in the arrangement of water molecules around the temperature of maximum density. The slight changes in the arrangement of water molecules in the first coordination sphere of Eu3+ ions due to the water density anomaly affect the variation with temperature of Eu3+ ions emission spectra and intensity decay time. This is the first time, to the best of our knowledge, that the effect of the anomaly in the density of water is detected by a luminescent material. From these experimental results we can infer that possibly the anomaly could be caused by variation in the length of hydrogen bonds between molecules with temperature for both water and heavy water.
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| 2. |
- Lastusaari, Mika, et al.
(author)
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The Bologna Stone: history's first persistent luminescent material
- 2012
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In: European Journal of Mineralogy. - : Schweizerbart. - 1617-4011 .- 0935-1221. ; 24:5, s. 885-890
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Journal article (peer-reviewed)abstract
- In 1603, the Italian shoemaker Vincenzo Cascariolo found that a stone (baryte) from the outskirts of Bologna emitted light in the dark without any external excitation source. However, the calcination of the baryte was needed prior to this observation. The stone later named as the Bologna Stone was among the first luminescent materials and the first documented material to show persistent luminescence. The mechanism behind the persistent emission in this material has remained a mystery ever since. In this work, the Bologna Stone (BaS) was prepared from the natural baryte (Bologna, Italy) used by Cascariolo. Its properties, e. g. impurities (dopants) and their valences, luminescence, persistent luminescence and trap structure, were compared to those of the pure BaS materials doped with different (transition) metals (Cu, Ag, Pb) known to yield strong luminescence. The work was carried out by using different methods (XANES, TL, VUV-UV-vis luminescence, TGA-DTA, XPD). A plausible mechanism for the persistent luminescence from the Bologna Stone with Cu+ as the emitting species was constructed based on the results obtained. The puzzle of the Bologna Stone can thus be considered as resolved after some 400 years of studies.
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| 3. |
- Mazzei, Laura, 1988, et al.
(author)
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Structure and Conductivity of Epitaxial Thin Films of In-Doped BaZrO3-Based Proton Conductors
- 2016
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:50, s. 28415-28422
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Journal article (peer-reviewed)abstract
- Epitaxial thin films of the proton-conducting perovskite BaZr0.53In0.47O3-delta H0.47-2 delta, grown by pulsed laser deposition, were investigated in their hydrated and dehydrated conditions through a multitechniqu approach with the aim to study the structure and proton concentration depth profile and their relationship to proton conductivity. The techniques used were X-ray diffraction, X-ray and neutron reflectivity, nuclear reaction analysis, and Rutherford backscattering, together with impedance spectroscopy. The obtained proton conductivity and activation energy are comparable to literature values for the bulk conductivity of similar materials, thus showing that grain-boundary conductivity is negligible due to the high crystallinity of the film. The results reveal an uneven proton concentration depth profile, with the presence of a 3-4 nm thick, proton-rich layer with altered composition, likely characterized by cationic deficiency. While this surface layer either retains or reobtains protons after desorption and cooling to room temperature, the bulk of the film absorbs and desorbs protons in the expected mariner. It is suggested that the protons in the near-surface, proton rich region are located in proton sites characterized by relatively strong O-H bonds due to weak hydrogen-bond interactions to neighboring oxygen atoms and that the mobility of protons in these sites is generally lower than in proton sites associated with stronger hydrogen bonds. It follows that strongly hydrogen-bonding configurations are important for high proton mobility.
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| 4. |
- Mazzei, Laura, 1988, et al.
(author)
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The effect of cation substitution on the local coordination of protons in Ba2In1.85M0.15O6H2 (M = In, Ga, Sc and Y)
- 2021
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In: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 365
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Journal article (peer-reviewed)abstract
- We report on an investigation of the local structure and vibrational dynamics in the brownmillerite-based proton conductors Ba2In1.85M0.15O6H2 with M = In, Ga, Sc and Y. The aim is to determine the effect of the cation (M) substitution on the local coordination environment of the protons. The techniques used are infrared spectroscopy and inelastic neutron scattering. The materials are characterized by two main types of proton sites, denoted as H (1) and H(2), which are featured by different local structures. We establish that the relative population of these two proton sites varies as a function of M. Specifically, it is found that, with respect to Ba2In2O6H2, the relative population of H(1) protons increases upon the substitution of In with any of the three different cations. The strongest effect is observed for M = Ga and Sc, whereas the effect observed for M = Y is minor. This new insight motivates efforts to unravel the mobility of the two types of protons, since then cation modification would offer a rational route for improving the proton conductivity of these types of materials.
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| 5. |
- Neto, Albano N. Carneiro, et al.
(author)
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Theoretical and Experimental Investigation of the Tb3+ -> Eu3+ Energy Transfer Mechanisms in Cubic A(3)Tb(0.90)Eu(0.10)(PO4)(3 )(A = Sr, Ba) Materials
- 2020
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:18, s. 10105-10116
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Journal article (peer-reviewed)abstract
- In this study the optical spectroscopy, the excited state dynamics, and in particular the Tb3+ -> Eu3+ energy transfer, have been investigated in detail both from the theoretical and experimental point of view in eulytite double phosphate hosts A(3)Tb(PO4)(3) (A = Sr, Ba) doped with Eu3+. It has been found that the energy transfer is strongly assisted by fast migration in the donor Tb3+ subset. Moreover, the transfer rates and efficiencies depend significantly on the nature of the divalent elements present in the structure and hence on the distances between Tb3+-Eu3+ nearest neighbors. It is shown that the competition between quadrupole-quadrupole and exchange interaction is crucial in accounting for the transfer rates.
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| 6. |
- Paterlini, Veronica, et al.
(author)
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Spectroscopic and Structural Properties of β-Tricalcium Phosphates Ca9RE(PO4)7 (RE = Nd, Gd, Dy)
- 2021
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In: Crystals. - : MDPI AG. - 2073-4352. ; 11:10
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Journal article (peer-reviewed)abstract
- Rare-earth-based Ca9RE(PO4)7 (RE = Nd, Gd, Dy) materials were synthesized by solid-state reaction at T = 1200 °C. The obtained tricalcium phosphate (TCP) materials are efficient light emitters due to the presence of RE3+ ions, although these ions are present at high concentrations. Moreover, in these host structures, these ions can be used as optical probes to study their local environments. Thus, photoluminescence (PL) emission spectra of the powder samples clearly indicated, for Dy3+ and Gd3+ ions, the presence of the RE3+ ion in low-symmetry sites with some local structural disorder, and the spectra show the presence of vibrational features (in the case of Gd3+). For the Nd3+ phase, emission bands are present around 900, 1050, and 1330 nm, originating from the 4F3/2 level. In general, these RE-TCP samples are interesting luminescent materials in the visible (Dy), UV (Gd), and NIR (Nd) regions, due to weak concentration quenching even for high concentrations of the emitting ion.
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| 7. |
- Sharma, Suchinder, 1982, et al.
(author)
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Photoluminescence Properties and Fabrication of Red-Emitting LEDs based on Ca9Eu(VO4)(7) Phosphor
- 2020
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In: ECS Journal of Solid State Science and Technology. - 2162-8777 .- 2162-8769. ; 9:1
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Journal article (peer-reviewed)abstract
- We study the photoluminescence properties of the red-emitting phosphor Ca9Eu(VO4)(7) and establish a strong red emission centered at 613 nm under excitation at 395 nm (near ultra violet light, near-UV light) due to the intra-configurational D-5(0) -> F-7(2) transition within the 4f(6) configuration of the Eu3+ ions. The intensity of the emitted light decreases with increasing temperature and at T = 470 K about 50% of the intensity of the emitted light at room temperature is lost. Five different red-LED prototypes were constructed by applying a mixture of Ca9Eu(VO4)(7) phosphor and silicone gel on the headers of near-UV LED chips. The prototypes showed a color output from violet for the lowest phosphor concentration (133 g phosphor /l silicone gel), reaching an almost pure red-light output for the highest phosphor concentration (670 g phosphor /l silicone gel). The luminous efficiency of optical radiation (LER) was found to decrease slightly with increasing applied current. For the highest phosphor concentration, the LER decreases from 238 lmW(-1) for 1 mA current supply to 235 lmW(-1) for 18 mA current supply. The external quantum efficiency decreased from 7.33% for the lowest phosphor containing LED prototype to 4.13% for the highest one. (C) The Author(s) 2019. Published by ECS.
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