Pairs Of Yb Research Articles

Dual-wavelength excited luminescence properties of NaYbF4:Er3+ for flexible anti-counterfeiting

Multiple encryption of information is the key to the upgrade of anti-counterfeiting technology. However, developing reliable multimode anti-counterfeiting materials is still a challenging work. Herein, a series of Er-doped NaYbF4 microprisms was synthesized. The as-prepared microprisms could show variable emission from red to yellow under the irradiation of 980 nm, and exhibit red at 365 nm UV light, respectively. Near-infrared excitation is achieved through the upconversion process of Er–Yb pairs, while UV excitation is achieved through Er ions. Its crystal structure, morphology, and photoluminescence features were analyzed. To broaden its practical application, the powders were combined with TPU to form a film with excellent stretchability, transparency, and water resistance. Our work demonstrates a dual-wavelength excited luminescence material, providing a practical reference for the application of anti-counterfeiting materials.

Low-temperature infrared spectroscopy of the strongly correlated semiconductor Tm0.19Yb0.81B12 with dynamic charge stripes

Tm1–x Yb x B12 dodecaborides represent model objects for the studies of quantum critical behavior, metal–insulator transitions (MITs) and complex charge-spin–orbital–phonon coupling phenomena. In spite of intensive investigations, the mechanism of semiconducting ground state formation both in YbB12 and in the Yb-based strongly correlated electron systems remains a subject of active debates. We have performed first systematic measurements of temperature-dependent spectra of infrared conductivity of Tm0.19Yb81B12 at frequencies 40–35 000 cm−1 and in the temperature range 10–300 K. Analysis of the temperature evolution of the observed absorption resonances is performed allowing to associate these with the cooperative dynamic Jahn–Teller instability of the boron sub-lattice. This ferrodistortive effect of B12-complexes induces the rattling modes of the rare earth ions leading to emergence of both the intra-gap mixed-type collective excitations and the dynamic charge stripes. We estimate the temperature-dependent effective mass of charge carriers and propose the scenario of transformation of the many-body states in the multiple relaxation channels. We attribute the MIT to the localization of electrons at the vibrationally coupled Yb–Yb pairs, which is accompanied by the electronic phase separation and formation of the nanoscale filamentary structure of electron density (stripes) in Tm1–x Yb x B12 compounds.

Enhancement of Near‐Infrared Phosphor Luminescence Properties via Construction of Stable and Compact Energy Transfer Paths

AbstractThe rapid development of near‐infrared (NIR) spectroscopy urgently requires the exploration of NIR‐emitting phosphors with excellent luminescence properties. Herein, GaTaO4:Cr3+,Yb3+ NIR phosphor with excellent luminescence properties is reported, which exhibits ultra‐broadband NIR emission with a full width at half maximum of 300 nm, good thermal stability of 90%@423 K, and most remarkably, high internal quantum efficiency of 95.5% and external quantum efficiency of 44.79%. Such outstanding luminescence properties mainly give the credit to the unique sandwiched structure of GaTaO4:Cr3+,Yb3+, in which layers of Yb3+ ions (activator) are sandwiched between layers of Cr3+ ions (sensitizer), and hence many stable and compact Cr–Yb pairs are formed, so that the energy can be rapidly transferred from Cr3+ to Yb3+, effectively activating the characteristic f–f transition of Yb3+ that is very stable and almost independent of the temperature, and at the same time, the non‐radiative transition of Cr3+ ions can be suppressed to a certain degree. The NIR phosphor‐converted light‐emitting diodes (pc‐LEDs) are fabricated by combining GaTaO4:Cr3+,Yb3+ with blue LED chips, and the application potential is fully demonstrated by non‐destructive food detection, night vision, and vein display. The results provide novel prospects for the design of NIR‐emitting materials with desirable luminescent properties.

Optical Properties of Molybdates Containing a Combination of Rare-Earth Elements

We have synthesized new molybdates, Cs2LnZrTi(MoO4)6.5 (Ln = Eu + Yb, Eu + Dy, and Gd + Dy lanthanides), containing pairs of rare-earth elements in the ratio 1 : 1. The synthesized compounds have been shown to be single-phase and isostructural with each other. We have determined their crystallographic characteristics and assessed their thermal stability. In the dysprosium-containing molybdates, the Dy3+ luminescence intensity is low as a result of concentration quenching. The molybdate containing the Eu + Dy pair of rare-earth elements shows predominant high-intensity luminescence in the red spectral region. In addition to usual infrared emission due to ytterbium, the Eu + Yb compound demonstrates emission in the ultraviolet spectral region. We have measured luminescence decay kinetic characteristics at the peak emission wavelengths. In the case of the molybdate containing the Eu + Yb pair of rare-earth elements, energy transfer from europium ions to ytterbium has been observed. We have demonstrated high-intensity luminescence that can be excited both on intraconfigurational transitions and in the region of charge transfer bands of oxygen–molybdenum complexes.

Electrical properties and light up conversion effects in Bi3.79Er0.03Yb0.18Ti3−xWxO12 ferroelectric ceramics

Modified ceramic compositions of Bi3.79Er0.03Yb0.18Ti3−xWxO12 with fixed Er and Yb content, and a varying W content (x=0.0, 0.01, 0.03, 0.06 and 0.10) are prepared. The site selectivity of Er3+, Yb3+, and W6+ cations is analyzed, and their influence on the electrical and light up conversion properties is studied. Formation of single phase orthorhombic structure is confirmed with enhanced grain growth up to x=0.03, and for (x≥0.04–0.10) the grain growth is inhibited, and the orthorhombic distortion is relaxed. Raman spectroscopy reveals W6+ cation substitutes preferentially at the B-site replacing Ti4+ ions in the Bi4Ti3O12 lattice structure. Increasing W6+ donor concentration reduces the conductivity effects by lowering the oxygen vacancies. Reduced dielectric losses (tan δ=0.003) and dispersion with frequency in the range (10−2–10Hz) are observed, and improvements in the remnant polarization (2Pr=28.86μC/cm2) are seen up to an optimum content of x=0.03. At higher W content (x>0.03), the properties tend to degrade due to structural relaxation and microstructural changes. Up conversion photoluminescence (UC-PL) under 980nm excitation shows strong emission in the green and red bands due to enhanced crystal field around the Er3+ ions for an optimum W content of x=0.06. A weak blue emission band around (~492nm) is observed by cooperative emission (CE) due to radiative relaxation of an excited Yb–Yb pair from a virtual level. Variation of UC emission intensity with pump-power confirms a two-photon mechanism for the up conversion process.

Cooperative and White Light Emission from Yb- and Yb,Er-Doped Y2Si2O7 Nanopowders

We have investigated the luminescence properties of of Y2Si2O7 nanopowders doped with (1) Yb only and (2) Yb and Er. Under 980 nm excitation of the Yb-only sample, the system exhibits a blue emission, which we attribute to cooperative emission from Yb pairs. When the air pressure in the sample holder is reduced to very low pressures, a broad band “white” emission, extending from the blue into the near IR, appears, and the blue Yb emission band disappears. In the Yb-Er doped system, no cooperative emission from Yb is observed, but the Er emission bands are observed throughout the visible region. These Er emissions result from upconversion processes through energy transfer or through a combination of energy transfer and excited state absorption. The broad band white light emission is also observed in this sample, and becomes the more favorable emission as the pressure is decreased and the pumping intensity increased.

Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li6Ln(BO3)3:Yb3+ (Ln=Gd, Y) Borate Single Crystals

Synthesized powders and grown single crystals of nominal compositions Li(6)Ln(BO(3))(3):Yb(3+) (Ln=Y, Gd) were investigated by means of powder and single-crystal X-ray diffraction (XRD), as well as optical near-IR spectroscopy in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The appearance of two distinct zero-phonon lines suggests the existence of two kinds of Yb(3+) ions in the single crystals. The XRD results exclude the possibility of a phase transition occurring between room and low temperatures. EPR spectra of single crystals show the presence of both isolated ions and pairs of ytterbium ions substituted for Y(3+). A strong temperature dependence of the intensity of Yb-Yb pairs resonance lines coincides with temperature dependence of emission peak at 978 nm, confirming a common origin of the defect giving rise to these spectra. Calculated from EPR spectra, the distance between pairs of Yb(3+) is in good agreement with crystallographic ones: R=3.856 Å, R(cryst) =3.849 Å.

Evolution of Yb 3+ environment and luminescence properties under ionizing irradiation in aluminoborosilicate glasses

Yb-doped aluminoborosilicate glasses were irradiated with 2.3 MeV electron and gamma rays at different doses ranging between 10 4 and 2.6 × 10 9 Gy and the local structure around the Yb 3+ ions has been studied using a combination of NMR, EPR and photoluminescence spectroscopic techniques. The spectroscopic results indicate the presence of two distinct Yb 3+ sites in these glasses and their relative fractions depend on both the Yb concentration and the irradiation dose. These two sites can be attributed to Yb 3+ ions with and without Yb next-nearest neighbors. The evolution of the shape of the 7F 5/2 → 7F 7/2 infrared emission band under irradiation is explained by a preferential reduction of the Yb 3+ ions with Yb next-nearest neighbors at high integrated doses (> 10 8 Gy). This interpretation is supported by a strong decrease of the visible cooperative luminescence under irradiation due to the reduction into the Yb pairs. In other terms, it shows an interesting effect of ionizing irradiation on the Yb clusters. A low intensity emission band appears in irradiated samples at 390 nm that can be attributed to Yb 2+. Finally, the decrease of the Yb 3+ fluorescence lifetime observed under irradiation appears to be primarily due to electronic interaction of these ions with Non-Bridging Oxygen Hole Centre defects created by the ionizing radiation.

Intense green upconversion emission in Tb^3+/Yb^3+ codoped alumino-germano-silicate optical fibers

We observed intense green upconversion emission from Tb(3+) centered at 546 nm due to transition D(4)5-->F(5)7 in Tb(3+)/Yb(3+) codoped alumino-germano-silicate optical fibers by direct excitation of Yb(3+) ions with a laser diode at 976 nm. A two-photon cooperative energy transfer upconversion among a pair of Yb(3+) donor ions and a Tb(3+) acceptor ion are responsible for the observed green emission. Appropriately increasing the concentration of Tb(3+) relative to Yb(3+) was found to facilitate the energy transfer upconversion process from Yb(3+) to Tb(3+), while an excess of Tb(3+) ions inversely introduced more of the concentration quenching effect and phonon-assistant backward energy transfer from Tb(3+) to Yb(3+) and, therefore, damaged the observed green emission. The intensity of the observed green emission was found optimum for a concentration ratio of Tb(3+) to Yb(3+) of 2:1 in alumino-germano-silicate optical glass fibers.

Role of Yb 3+ and Tm 3+ ions in upconversion emission of Tb 3+ under 798 and 980 nm laser excitations in Tb 3+–Tm 3+–Yb 3+ doped tellurite glass

Upconversion emission and energy transfer processes in singly, doubly and triply doped tellurite glasses have been studied under 798 and 980 nm laser excitations. Emissions have been observed at 482, 544, 584, 655 nm and at 477, 655, 698, 800 nm corresponding to Tb 3+: 5D 4 → 7F 6, 7F 5, 7F 4, 7F J ( J = 0, 1, 2, 3) and Tm 3+: 1G 4 → 3H 6, 1G 4 → 3F 4, 3F 3 → 3H 6, 3H 4 → 3H 6 transitions, respectively. Among Tm 3+, Yb 3+and Tb 3+ ions only Tm 3+ has a ground state absorption at 798 nm excitation due to 3H 4 ← 3H 6 transition. For 980 nm excitation only Yb 3+ can absorb the incident radiation. However, for both types of excitations, emission from all the three ions Tb, Yb and Tm has been observed. Possible mechanisms are proposed as follows: under 798 nm excitation Tm 3+ ions are excited which excite Yb 3+ ions through energy transfer. Finally “cooperative energy transfer” from a pair of Yb 3+ ions to Tm 3+ and Tb 3+ ions takes place. Under 980 nm excitation Yb 3+ ions absorb the incident energy and excite Tm 3+ and Tb 3+ ions via cooperative energy transfer. Variation of emission intensity with the ion concentrations of Yb 3+, Tm 3+ and Tb 3+ has been studied. The lifetime of the 1G 4 level has also been measured.

EPR results and Raman spectroscopy as a complementary characterization of isolated Yb ions and Yb pairs in CaF2:Yb single crystals

Raman spectrum of the CaF 2 :Yb crystal irradiated with γ-rays shows the localized phonon centred at about 64 cm -1 being an evidence of the ytterbium pairs presence. There are not observed absorption bands characteristic for Yb 2+ ions in the absorption spectrum of as-grown (not irradiated or not annealed) CaF 2 :Yb (5 mol%) crystal. Electron paramagnetic resonance measurements of CaF 2 :Yb (5 mol%) single crystals were carried out for lattice sites substituted by Yb 3+ ions and also for the possibility of ytterbium pairs arising. Among eight of EPR lines observed for as-grown crystal, mainly the lines originating from different Yb 3+ isotopes can be distinguished: 170 Yb 3+ Ι = 0, 171 Yb 3+ 1= 1/2 and 1?3 Yb 3+ Ι=5/2. The lines originating from Yb 3+ pairs cannot be excluded. All of the lines do not move with angular variation in the planes parallel and perpendicular to the axis. The extra line in the magnetic field orientation in every plane at 45°, with B 0 ∼ 191 mT is observed. This unidentified line corresponds to a non-axial Yb 3+ centre or unknown impurity. The components of A and g tensors of the spin Hamiltonian for cubic symmetry were calculated. Temperature dependence of the EPR lines shows the agreement with the Curie law until the temperature of 18 K. The peak-to-peak linewidth changes continuously within 20 mT range for as-grown crystals, while shows significant linear increase above 18 K for γ-irradiated ones. It suggests the presence of Yb 2+ ions, being created due to Compton electron capture. So, Yb 3+ co-exists with Yb 2+ after the Yb 3+ → Yb 2+ conversion under influence of γ-irradiation. It seems the Yb 2+ centres arising in CaF 2 :Yb (5 mol%) single crystal irradiated with γ-quanta are related to Yb 3+ , as an effect of recharging one of Yb 3+ ion from a pair, or form Yb 3+ -Yb 2+ pair when Compton electron is captured by one of isolated neighbour Yb 3+ ions.

Strong Visible Cooperative Up-Conversion Emission in ZrO<SUB>2</SUB>:Yb<SUP>3+</SUP> Nanocrystals

Blue, green, and red emission was observed under infrared excitation in ZrO2:Yb3+ nanocrystals prepared by the sol-gel process. The structural characterization was performed by using XRD and HRTEM, suggesting that the crystalline phase of the nanoparticles is controlled by the active ion concentration being mainly tetragonal for 2 mol% of dopant and mainly monoclinic for 0.5 mol%. The blue emission was explained in terms of the cooperative deexcitation of an Yb-Yb pair, while the green and red bands were associated with the up-conversion of traces of Er ion. The number of photons involved in the luminescence process is analyzed in order to confirm that cooperative emission is produced by the interaction of an Yb pair and that the green and red emission are the results of energy transfer between Yb-Er ions. The high efficiency of all bands is explained in terms of the high surface area of the nanoparticles.

Thermally enhanced cooperative energy-transfer frequency upconversion in terbium and ytterbium doped tellurite glass

Infrared-to-visible frequency upconversion through cooperative energy-transfer and thermal effects in Tb3+/Yb3+-codoped tellurite glasses excited at 1.064μm is investigated. Bright luminescence emission around 485, 550, 590, 625 and 655nm, identified as due to the 5D4→7FJ (J=6, 5, 4, 3, and 2) transitions of the terbium ions, respectively, was recorded. The excitation of the 5D4 emitting level of the Tb3+ ions is assigned to cooperative energy-transfer from pairs of ytterbium ions. The effect of temperature on the upconversion process was examined and the results revealed a fourfold upconversion enhancement in the 300–500K interval. The enhancement of the upconversion process is due to the temperature dependence of the Yb3+-sensitizer absorption cross-section under anti-Stokes excitation. A rate-equation model using multiphonon-assisted absorption for the ytterbium excitation combined with the energy migration effect between Yb–Yb pair and Tb3+ ground-state depopulation via multiphonon excitation of the 7FJ excited states describes quite well the experimental results.

The Independent Yellow Channel For Tetrachromatic Imaging

Imaging systems tend at first to simulate the opponent yellow and blue vision channels (YB) even if that perceptibly violates trichromatic simulation of opponent red and green channels (RG). The preference is biologically traced: 8% male population are deficient in RG vision and only 0.003% in YB vision. The YB pair is not the usually assumed alternating combination of M, L, and S-cone responses (say, L+M-S): it is independent of RG sensations (L-M). The complementary yellow (570) and blue (465 nm) are seen after the RG pair has disappeared with decreasing illumination. The yellow is not seen after the 650-nm sensitivity limit of rhodopsin even if the red is over 50 nm more. The ‘blue-cone monochromats’ and some protanopes, having no M and L-cones, see the YB pair. Yellow adaptation eliminates the YB sensations but hardly influences the RG pair. Reflectometry of living retinas shows the ‘M and S-cone pigments’ rather to be long-living products of iodopsin (L-pigment) and rhodopsin.

Extraction of micro- and macroconcentrations of rare earth ions with the mixture of D2EHPA and TBP in n-hexane and cyclohexane

The synergistic solvent extraction of Eu(III) and some other rare earth elements from nitrate solutions (HNO3+LiNO3) by a mixture of (TBP+D2EHPA) in n-hexane and cyclohexane has been investigated at 22 °C. Antagonism found in europium extraction from 0.1M HNO3 transforms into a synergistic effect. The synergistic effects existing for all investigated metals in extraction from 0.1M HNO3+3M LiNO3 were caused by formation of mixed complexes of the type Ln(D2EHPA)2nH2n−3+1(NO3)1TBPm, where 1=1 or 2. The selectivity of the extraction in a synergistic system is lower for the La−Yb pair than in the case of D2EHPA extraction under the same conditions. On the other hand, the application of the synergistic mixture is more suitable for Eu−Ho separation. Thus the synergistic effect can be used for the separation or refining of some lanthanides.

Effect of temperature on the selectivity of the extraction of lanthanides with dibutylphosphoric acid from thiocyanate solution

Extraction coefficients and separation factors of all lanthanides were determined in the system: dibutylphosphoric acid /HDBP/ - 3M NH4NCS, in the temperature range of 15–50 °C. The values for the separation factors for such pairs as: Gd−Tb and Er−Tm, are higher than 4, those for the pair of Tb−Dy are higher than 3, and those for the La−Ce, Pm−Sm, Dy−Ho, Ho−Er and Tm−Yb pairs are higher than 2. The influence of temperature on the separation factors of light /La−Gd/ and heavy /Gd−Lu/ lanthanides is discussed and compared with that observed for the extraction from the nitric acid solutions. The results are also discussed in the light of the double-double effect and outer-, vs. inner-sphere complexation in the lanthanide series.