U. Caldiño

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David Stuart

The University of Texas at Austin

Dr. Sovan Kumar Panda

Central Glass and Ceramic Research Institute (CSIR), Calcutta

Amos Frumkin

The Hebrew University of Jerusalem

Jean-Jacques Hublin

Max Planck Institute for Evolutionary Anthropology

Johnni Langer

UFPB - Universidade Federal da Paraíba

Davide Domenici

Università di Bologna

Vasilios Melfos

Aristotle University of Thessaloniki

Alexandre Tokovinine

University of Alabama - Tuscaloosa

Gísli Sigurðsson

The Árni Magnússon Institute for Icelandic Studies

Airán Ródenas

Universidad de La Laguna

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Papers by U. Caldiño

Zinc doping effect on the optical bands of cr3+in LiNbO3: Zn, Cr crystals

Ferroelectrics Letters Section, 1994

ABSTRACT

Survey of optical and fluorescence traits of Tm3+-doped alkali/mixed alkali oxides constituting B2O3-BaO-ZnO-LiF glasses for 0.45 μm laser and 1.46 μm fiber amplifier

Results in Physics, 2021

Survey of optical and fluorescence traits of Tm 3+-doped alkali/mixed alkali oxides constituting ... more

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Synthesis of luminescent terbium-thenoyltriflouroacetone MOF nanorods for green laser application

Optical Materials, 2019

The metalorganic frameworks (MOFs) with lanthanides ions offer great potential in the optical are... more The metalorganic frameworks (MOFs) with lanthanides ions offer great potential in the optical area because can provide properties of flexibility, low density, low-cost methods of synthesis, and insolubility in water, which give them an advantage over traditional phosphors. In this study, a thenoyltriflouroacetone ligand (TTA) with a Tb 3+ MOF was synthesized (Tb = 10 and 50% mol) and its structural and luminescent properties were analyzed. The metalorganic compound was generated in a simple one-pot reaction from terbium nitrate and 2-thenoyltrifluoroacetone precursors at room temperature. By means of FTIR, it was confirmed the presence of carbon groups, which made possible the terbium ion chelation, and also the Tb-O bonds vibration modes. 1 HNMR results confirm that the complex with 10% mol of Tb 3+ contains three coordinates molecules of TTA and two waters molecules. The powders exhibit rod-like morphology with size about 170 nm of diameter and a length about 2 μm; the rod-like nature of powders was confirmed by SEM and TEM analyses. By XRD it was concluded that at higher terbium concentration (TTA-50Tb sample) higher the crystallite size and crystallinity, in fact the TTA-10Tb sample shows a partial-amorphous nature. By photoluminescence analyses, the 5 D4→ 7 FJ (J = 3, 4, 5 and 6) emissions were recorded for both synthesized samples (λexc = 376 nm). Furthermore, it was observed that the emission intensity was enhanced in a factor of 3.5 for the TTA-50Tb. The energy transfer efficiency from TTA to Tb 3+ (antenna effect) was 0.984 for TTA-10Tb and 0.993 for TTA-50Tb. Decay time analyses indicate effective lifetime of 1.45 and 1.60 m s for the samples doped at 10 and 50%, respectively, indicating that the forbidden transition rules are stronger at higher crystallinity. The integrated intensities of the 5 D4 → 7 F5 (green at 541 nm) and 5 D4 → 7 F6 (blue at 486 nm) emissions and their intensity ratios IG/IB upon 376 nm excitation have been evaluated for TTA-10Tb andTTA-50Tb samples. The CIE1931 color of the MOFs excited at 376 nm attains a higher green color purity by increasing the terbium concentration. This is in concordance with the increased IG/IB ratio up for the TTA-10Tb and TTA-50Tb samples. Thus, the TTA-50Tb sample exhibits a green color purity of 67.94% with chromaticity coordinates (0.30, 0.57), being very close to those (0.29, 0.60) of European Broadcasting Union illuminant green. This interesting feature of the TTA-50Tb sample, together with an experimental branching ratio of 61.3% for the 5 D4 → 7 F5 green emission, highlights its capability as solid state green laser pumped by GaN (376 nm) LEDs.

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Effect of alkali/mixed alkali metal ions on the thermal and spectral characteristics of Dy3+:B2O3-PbO-Al2O3-ZnO glasses

Journal of Non-Crystalline Solids, 2018

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Structural and optical studies of Er 3+ -doped alkali/alkaline oxide containing zinc boro-aluminosilicate glasses for 1.5 μm optical amplifier applications

Optical Materials, 2017

In the present work, we report on the optical spectral properties of Er3+-doped zinc boroaluminos... more In the present work, we report on the optical spectral properties of Er3+-doped zinc boroaluminosilicate glasses with an addition of 10 mol % alkali/alkaline modifier regarding the fabrication of new optical materials for optical amplifiers. A total of 10 glasses were prepared using melt−quenching technique with the compositions (40-x)B2O3 − 10-SiO2 − 10Al2O3 − 30ZnO − 10Li2O − xEr2O3 and (40-x)B2O3 − 10SiO2 − 10Al2O3 − 30ZnO-10MgO − xEr2O3 (x = 0.1, 0.25, 0.5, 1.0, and 2.0 mol %). We confirm the amorphous-like structure for all the prepared glasses using X-ray diffraction (XRD). To study the functional groups of the glass composition after the melt−quenching process, Raman spectroscopy was used, and various structural units such as triangular and tetrahedral-borates (BO3 and BO4) have been identified. All the samples were characterized using optical absorption for UV, visible and NIR regions. Judd-Ofelt (JO) intensity parameters (Ωλ , λ = 2, 4 and 6) were calculated from the optical absorption spectra of two glasses LiEr 2.0 and MgEr 2.0 (doped with 2 mol % of Er3+). JO parameters for LiEr 2.0 and MgEr 2.0 glasses follow the trend as Ω6>Ω2>Ω4. Using Judd-Ofelt intensity parameters, we obtained radiative probability A (S−1), branching ratios (β), radiative decay lifetimes τrad (μs) of emissions from excited Er+3 ions in LiEr 2.0 and MgEr 2.0 to all lower levels. Quantum efficiency (η) of 4 I13/2 and 4 S3/2 levels for LiEr 2.0 and MgEr 2.0 with and without 4D7/2 level was calculated using the radiative decay lifetimes τrad. (μs) and measured lifetimes τexp. (μs). We measured the visible photoluminescence under 377 nm excitation for both LiEr and MgEr glass series within the region 390-580 nm. Three bands were observed in the visible region at 407 nm, 530 nm, and 554 nm, as a result of 2H9/2 → 4 I15/2 , 2H11/2 → 4 I15/2 and 4 S3/2 → 4 I15/2 transitions, respectively. Decay lifetimes for emissions at 407 nm, 530 nm, and 554 nm were measured and they show single exponential behavior for all the LiEr and MgEr glass series. From the photoluminescence and radiative decay lifetimes (τrad), we calculated the full-width at halfmaximum (FWHM), emission cross-section () and bandwidth gain (FWHM) parameters. Near-infrared photoluminescence under 980 nm excitation was measured for all the LiEr and MgEr glass series in the region 1420-1620 nm. NIR emissions show a broadband centered at ∼1530 nm due to the transition of Er3+: 4 I13/ 2 → 4 I15/2. Decay lifetimes for NIR emission at ∼1530 nm were measured and they show a quite exponential nature for all the LiEr and MgEr glass series. From the NIR emission spectra and decay lifetimes, we calculated the full-width at half-maximum (FWHM), the emission cross-section () and the bandwidth gain (FWHM) for the NIR emission and it shows FWHM of 50-70 nm for prepared glasses, emission cross-section of (∼3.5) 10−20 cm2 , while bandwidth gain was (∼25) 10−26 cm3.

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Orange and reddish-orange light emitting phosphors: Sm3+ and Sm3+/Eu3+ doped zinc phosphate glasses

Journal of Luminescence, 2015

A spectroscopy study of Sm 3 þ and Sm 3 þ /Eu 3 þ doped zinc phosphate glasses is performed throu... more A spectroscopy study of Sm 3 þ and Sm 3 þ /Eu 3 þ doped zinc phosphate glasses is performed through photoluminescence spectra and decay time profile measurements. Under Sm 3 þ excitation at 344 nm, the Sm 3 þ singly doped glass shows an orange global emission with x ¼ 0.579 and y¼0.414 CIE1931 chromaticity coordinates, whereas the Sm 3 þ /Eu 3 þ co-doped sample exhibits orange overall emissions (x ¼0.581 and y¼ 0.398, and x ¼0.595 and y¼0.387) and reddish-orange overall emission (x ¼0.634 and y¼ 0.355) upon excitations at 344, 360 and 393 nm, respectively. Such luminescence from the co-doped sample is originated by the simultaneous emission of Sm 3 þ and Eu 3 þ. Under Sm 3 þ excitation at 344 and 360 nm, the Eu 3 þ emission is sensitized and enhanced by Sm 3 þ through a non-radiative energy transfer process. The non-radiative nature was inferred from the shortening of the Sm 3 þ lifetime observed in the Sm 3 þ /Eu 3 þ co-doped sample. An analysis of the Sm 3 þ emission decay time profiles using the Inokuti-Hirayama model suggests that an electric quadrupole-quadrupole interaction into Sm-Eu clusters might dominate the energy transfer process, with an efficiency of 0.17.

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Rare Earth Doped Glasses for Displays and Light Generation

13th International Ceramics Congress - Part D, 2014

Glasses are very versatile materials, also because of the ease of doping them with various elemen... more Glasses are very versatile materials, also because of the ease of doping them with various elements and compounds. In particular, rare-earth-doped glasses have greatly contributed to the development of optical amplifiers, lasers, active optical waveguides and white-light-emitting devices. White light emitting diodes (W-LEDs) and color LEDS obtained by the combination of an UV emitting LED, such as AlGaN-based LED, with a glass phosphor exhibit very interesting properties. In the present contribution we report the luminescence characteristics of zinc-sodium-aluminosilicates glasses variously doped, namely either singly doped with Eu3+, Tb3+ or Sm3+, or co-doped with Tb3+-Eu3+, Tb3+-Sm3+ and Tb3+-Ce3+. These glasses have also proved to be suitable for ion exchange and therefore for the production of active optical waveguides.

Spectroscopic characterization and optical waveguide fabrication in Ce 3+, Tb3+ and Ce3+/Tb3+ doped zinc-sodium-aluminosilicate glasses

A spectroscopy investigation of Ce3+ and Tb3+ ions in sodium–zinc–aluminosilicate glasses is perf... more A spectroscopy investigation of Ce3+ and Tb3+ ions in sodium–zinc–aluminosilicate glasses is performed using the photoluminescence technique. Blue–white light, with x= 0.24 and y= 0.24 CIE chromaticity coordinates, is obtained for the Tb3+ singly-doped glass excited at 351nm. When the sodium–zinc–aluminosilicate glass is co-doped with Ce3+ and Tb3+ a non-radiative energy transfer from Ce3+ to Tb3+ ions is observed upon 320nm excitation. From an analysis of the cerium emission decay curve, the Ce3+→ Tb3+ energy ...

Judd-Ofelt analysis of the B-Te-Na-Si-Al:Er3+ polymolecular glass for IR broadband telecommunication

SPIE Proceedings, 2011

ABSTRACT The main spectroscopic properties of a new B-Te-Na-Si-Al:Er3+ glass are investigated. Th... more ABSTRACT The main spectroscopic properties of a new B-Te-Na-Si-Al:Er3+ glass are investigated. The Judd-Ofelt (JO) intensity parameters (Ωt), the spontaneous emission probabilities, the branching ratios and the radiative lifetimes for each observed Er3+-ion levels were determined. The stimulated emission cross section, the fluorescence full width at half maximum (FWHM), Δλeff, the Δλeff x σe factor, and the gain spectra of the main Er3+-ion lasing emission (4I13/2--&gt;4I15/2) are obtained after exciting the glass sample at 532 nm (4I15/2 --&gt;4S3/2 ). The absorption cross section of the 4I15/2--&gt;4I13/2 transition of the Er3+-ions was also obtained from absorption spectrum of the new glass. The results are compared with those reported for other Er3+-doped oxide glasses pumped at various excitation wavelengths, indicating the new Er3+- doped boro-tellurite glass has potential properties as an optical amplifier in the C-telecommunication window (1.53 μm) and a IR tunable laser. Additionally a radiative energy transfer from the glass host to the Er3+-ions was observed at 520 nm by exciting the glass sample at 466 nm into the Er3+-ion dark region.

Soda-zinc-aluminosilicate glasses doped with Tb3+, Ce3+, and Sm3+for frequency conversion and white light generation

SPIE Proceedings, 2011

Abstract Sodium-zinc-aluminosilicate (NaZAS) glasses doped with single or multiple rare earth ion... more Abstract Sodium-zinc-aluminosilicate (NaZAS) glasses doped with single or multiple rare earth ions (Ce3+, Tb3+, Sm3+) were synthesized, and their characteristics investigated by m-line spectroscopy, absorption and luminescence spectroscopy, and micro-Raman spectroscopy. Blue-white light, with x= 0.24 and y= 0.24 CIE chromaticity coordinates, was obtained for the Tb3+ singly-doped glass excited at 351 nm. In NaZAS glasses co-doped with Ce3+ and Tb3+ it was possible to observe a non-radiative energy transfer from Ce3+ ...

Nd3+→Yb3+resonant energy transfer in the ferroelectricSr0.6Ba0.4Nb2O6laser crystal

Physical Review B, 2008

Resonant ͑nonphonon-assisted͒ Nd 3+ → Yb 3+ energy transfer has been observed in Nd 3+ and Yb 3+ ... more Resonant ͑nonphonon-assisted͒ Nd 3+ → Yb 3+ energy transfer has been observed in Nd 3+ and Yb 3+ codoped Sr 0.6 Ba 0.4 ͑NbO 3 ͒ 2 crystals. The Nd 3+ → Yb 3+ energy transfer in this system has been compared to those taking place in other Nd 3+-Yb 3+ codoped hosts, for which, in most of cases, the transfer is only possible by assistance of phonons. The resonant nature is explained as a result of both the very broad optical bands of Nd 3+ and Yb 3+ ions in Sr 0.6 Ba 0.4 ͑NbO 3 ͒ 2 and the short energy gap ͑636 cm −1 ͒ between the 4 F 3/2 ͑Nd 3+ ͒ and 2 F 5/2 ͑Yb 3+ ͒ excited states. Spectroscopic data revealed that the energy transfer occurs via a nonradiative process and is dominated by an electric dipole-dipole interaction. The most relevant spectroscopic properties of the Nd 3+ → Yb 3+ energy transfer have been systematically investigated as a function of Yb 3+ ion concentration. The energy transfer efficiency increases linearly with the Yb 3+ ion concentration so that about a 50% is attained for a 10 at. % of ion acceptor concentration.

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Optical Spectroscopy of Mn2+ Ions in CaF2

physica status solidi (b), 1999

ABSTRACT Available from http://www3.interscience.wiley.com/cgi- bin/abstract/55002705/START

Luminescence properties of Ce3+–Dy3+ codoped aluminium oxide films

Optical Materials, 2011

Photoluminescence properties of CeCl 3 and DyCl 3 codoped aluminium oxide films deposited by the ... more Photoluminescence properties of CeCl 3 and DyCl 3 codoped aluminium oxide films deposited by the ultrasonic spray pyrolysis technique were characterized by excitation, emission and decay time spectroscopy. When excited by ultraviolet radiation the films emit a combination of blue and yellow wavelengths through an efficient energy transfer from Ce 3+ to Dy 3+ ions (up to around 77%). From spectroscopic data it is inferred that such energy transfer is nonradiative in nature taking place between Ce 3+ and Dy 3+ clusters through a short-range interaction mechanism. In the Ce 3+ doped single film the chromaticity coordinates are in the purplish blue region, whereas that in the cerium and dysprosium codoped films the coordinates move toward the white light emission region.

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Optical spectroscopy of Dy3+ ions in LiNbO3

Optical Materials, 1996

A systematic spectroscopic study of Dy '+ doped LiNbO, is presented. The energy position of the S... more A systematic spectroscopic study of Dy '+ doped LiNbO, is presented. The energy position of the Stark levels and their symmetry character is given for most of the multiplets. Luminescence of this system has been investigated in the visible and infrared. The only emitting state in this region is the metastable 4F a,? multiplet whose life time is temperature independent and with a value of 186 ps. Evidence about Dy3+ multicentres is also discussed.

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Optical spectroscopy of Er3+ ions in poly(acrylic acid)

Optical Materials, 2006

Er 3+-doped poly(acrylic acid) was synthesized by polymerization in aqueous solution of the monom... more Er 3+-doped poly(acrylic acid) was synthesized by polymerization in aqueous solution of the monomer partially neutralised with erbium hydroxide. 13 C NMR spectra confirmed the monomer modification. Absorption intensity data of the Er 3+ lanthanide ion in poly(acrylic acid) (PAA) are analysed using the Judd and Ofelt (JO) phenomenological treatment in order to understand its optical properties for laser application. The intrinsic emission of PAA gives rise radiative energy transfer between the host and Er 3+ ions. The measured and calculated oscillator strengths for transitions from the ground state to excited multiplets compare favourably within the typical uncertainties associated with the JO formalism. Then, the spontaneous radiative transition probabilities from the former 11 excited states to diverse ending states were computed to obtain the luminescence branching ratios as well as the radiative lifetimes.

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Luminescence properties of terbium doped poly(acrylic acid) containing 1,10-phenanthroline and 2,2′-bipyridine

Optical Materials, 2006

Tb 3+-doped poly(acrylic acid) was synthesized by polymerization in aqueous solution of the monom... more Tb 3+-doped poly(acrylic acid) was synthesized by polymerization in aqueous solution of the monomer partially neutralized with Tb 2 O 3 , using potassium persulfate as initiator. Besides, samples containing Tb 3+ and 1,10-phenanthroline (Phen) or 2,2 0-bipyridine (Bipy) ligands were synthesized. 13 C NMR confirmed the monomer modification and coordination of ligands to Tb 3+. The doped polymer was characterized by Fourier transform infrared (FT-IR) and luminescent spectroscopy. The results showed clear evidence of the coordination between the dopant cations and the carboxylate anions from the polymer, which were formed during the partial neutralization of the monomer prior to polymerization, and confirmed the coordination of Phen or Bipy ligands to Tb 3+. On the other hand, the broadening and the relatively high intensity of the 5 D 4 ! 7 F 5 green emission of Tb 3+ indicate that the dopant ions are uniformly distributed in low symmetry coordination sites into the polymer matrix. Additionally, the complex formation of Tb 3+ and Phen or Bipy resulted in a prominent enhancement in the Tb 3+ emissions attributed to antenna effect, defined as the excitation of the ligands by light absorption and efficient energy transfer from the ligands to the Tb 3+ ions. The luminescent results showed that, for these polymeric materials, the antenna effect of Phen is even better than that of Bipy.

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Photoluminescence of Ce3+and Mn2+in zinc metaphosphate glasses

Journal of Physics: Condensed Matter, 2005

Abstract The spectroscopic characterization of zinc metaphosphate glasses, singly and doubly dope... more Abstract The spectroscopic characterization of zinc metaphosphate glasses, singly and doubly doped with Ce3+ and Mn2+ ions, is performed through excitation and emission spectra and decay time measurements. The weak yellow emission of Mn2+ is significantly enhanced by means of an efficient energy transfer from Ce3+ to Mn2+ ions. The efficiency of the energy transfer has been estimated based on spectroscopic data, and turned out to be about 53%. From spectroscopic data it can also be inferred that the energy transfer is ...

Spectroscopic characterization of Er3+transitions in Bi4Si3O12

Journal of Physics: Condensed Matter, 2004

A systematic investigation of optical absorption and luminescence is presented for Er3+ ions in t... more A systematic investigation of optical absorption and luminescence is presented for Er3+ ions in the Bi4Si3O12 crystal. The intrinsic emission of this crystal gives rise to a radiative energy transfer among the host lattice and Er3+ ions. Measured oscillator strengths for seven different transitions from the ground state to excited state manifolds compare favourably with the electric dipole oscillator strengths

Optical spectroscopy of Nd3+ions in poly(acrylic acid)

Journal of Physics: Condensed Matter, 2006

Nd3+ dissolved in solid poly(acrylic acid) was synthesized by polymerization of the monomer parti... more Nd3+ dissolved in solid poly(acrylic acid) was synthesized by polymerization of the monomer partially neutralized with neodymium hydroxide in aqueous solution. The monomer modification and the coordination of ligands to Nd3+ were confirmed by 1H NMR spectroscopy. The measured oscillator strengths for transitions from the ground state to the main excited state manifolds compared favourably with calculated electric dipole oscillator

Cold white light generation from hafnium oxide films activated with Ce3+, Tb3+, and Mn2+ ions

Journal of Materials Research, 2010

Hafnium oxide films doubly doped with CeCl3 and TbCl3 and triply doped with CeCl3, TbCl3, and MnC... more Hafnium oxide films doubly doped with CeCl3 and TbCl3 and triply doped with CeCl3, TbCl3, and MnCl2 were deposited at 300 °C with the ultrasonic spray pyrolysis technique. The green and yellow emissions of Tb3+ ions and the yellow-red emission of Mn2+ ions can be generated upon ultraviolet (UV) excitation via a nonradiative energy transfer from Ce3+ to Tb3+ and Ce3+ to Mn2+. In the doubly doped film Ce3+ → Tb3+ energy transfer via an electric dipole–quadrupole interaction appears to be the most probable transfer mechanism; the efficiency of this transfer is about 81% upon excitation at 270 nm. In the HfO2 films activated with Ce3+, Tb3+, and Mn2+ the efficiency of energy transfer from Ce3+ to Tb3+ and Mn2+ ions is enhanced by increasing the Mn2+ concentration, up to about 76% for the film with the highest manganese content (1.6 at.%). In addition, it is demonstrated that these triply doped films can generate cold white light emission upon excitation at 270 nm (peak emission wave len...