Excited Yb Research Articles

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.

Improving broadband emission within Bi/Er doped silicate fibres with Yb co-doping

We present Bi/Er/Yb co-doped silicate fibre (BEYDF) which is fabricated by co-doping with Yb2O3 into Bi/Er doped silicate fibre (BEDF), and investigate its properties associated with Yb co-doping. Spectral absorption, emission, emission lifetime, ESA and gain characteristics of BEYDF are experimentally investigated and compared with those of BEDF to reveal particular impacts of Yb on the broadband spectral characteristics. We measured Yb3+ emissions at 980 nm and 1040 nm in BEYDF, and emissions related to Bi active centres (BACs, at 1100 nm and 1420 nm) and Er3+ (1530 nm) in BEYDF and BEDF under 830 nm pumping. Evidences of Yb3+→BAC energy transfer process, in addition to the normal Yb3+→Er3+ energy transfer process are noticed. Compared with BEDF, BEYDF has shown both broadened and enhanced emissions and gain. In particular, the overall emission bandwidth within a 4 dB intensity is attained over Δλ = (1000−1590) nm in BEYDF, and just over Δλ = (1250−1590) nm in BEDF. The overall emission intensity is enhanced by a factor of 2.5 in BEYDF over that of BEDF. Furthermore, Er3+ gain at 1530 nm is increased and BAC linked ESA at 1400 nm is reduced in BEYDF. Yb3+ related emissions and energy transfers from the excited Yb3+ to both the Er3+ and BACs can explain the improvements of emission and gain. These results indicate that Yb3+ co-doping can be used to expand and enhance broadband emissions and gain in BEYDFs.

Blue upconversion of Tm3+ using Yb3+ as energy transfer bridge under 1532 nm excitation in Er3+, Yb3+, Tm3+ tri-doped CaMoO4

Nano-sized CaMoO4 phosphors tri-doped with Er3+, Yb3+ and Tm3+ ions were successfully synthesized by sol-gel method. Intense blue emission from Tm3+ ions was observed upon excitation of 1532 nm infrared light in Er-Yb-Tm system, while this blue upconversion could not be achieved with the absence of Yb3+ ions in Er-Tm co-doped sample. In order to understand this upconversion process, the upconversion spectra in these samples were investigated, and the possible mechanism was proposed based on experimental results. It showed that two different energy transfer from Er3+ to Tm3+ existed simultaneously in Er-Yb-Tm system, the one-step direct energy transfer from Er3+ to Tm3+, and the two-step Er3+→Yb3+→Tm3+ energy transfer. In particular, the 1G4 state of Tm3+ could only be populated from the 3H4 state by cross-relaxation with an excited Yb3+ ion, producing blue emission of Tm3+. In this upconversion process, Yb3+ ions acted as an energy transfer bridge between Er3+ and Tm3+, which also meant that the upconversion of other rare-earth ions under the excitation of 1532 nm was possible with the presence of Er3+ and Yb3+.

Low-threshold mode instability in Yb3+-doped few-mode fiber amplifiers.

Spatio-temporal instability of the fundamental mode in Yb(3+)-doped few-mode PM fiber amplifiers with a core diameter of 8.5 μm was registered at 2-30 Watts pump power. Both experimental and theoretical analysis revealed the nonlinear power transformation of the LP(01) fundamental mode into high-order modes. Numerical simulation revealed self-consistent growth of the higher-order mode and traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb(3+) ions). Experimental results and numerical calculations showed the increase of the instability threshold along with an increase of the signal frequency bandwidth.

Nanostructure and luminescence properties of amorphous and crystalline ytterbium–yttrium oxide thin films obtained with pulsed reactive crossed-beam deposition

The nanostructure of ytterbium-doped yttrium oxide thin films, produced using pulsed laser ablation of a Yb–Y alloy target together with a pulsed flow of oxygen, is examined using X-ray and electron diffraction as well as Scanning Transmission Electron Microscopy (STEM). As-produced coatings are amorphous and become nanocrystalline cubic yttria after annealing. STEM images taken in the Bright-Field (BF) and in the High-Angle Annular Dark-Field (HAADF) modes reveal different aspects of the nanostructure of yttria. Simulations of the bixbyite structure of yttria indicate that dark spots arranged in a honeycomb structure seen in the STEM-BF mode arise from the absence of oxygen ions at regular crystallographic locations, while those seen on the HAADF images arise from cationic distortions. These results spectacularly exemplify the complementarity of the BF and HAADF imaging modes. Luminescence properties of amorphous and crystalline samples are also studied. Excitation of Yb3+ ions with an infrared (IR) laser diode produce both IR luminescence from excited Yb3+ and visible luminescence from holmium impurities present in the starting materials. Yb3+ emission bands become increasingly narrower as crystallization takes place, testifying for the transition from inhomogeneous to homogeneous crystal field. Increased lifetime and more intense luminescence observed after annealing imply reduced nonradiative relaxation and higher quantum efficiency.

Multi-ion cooperative processes in Yb3+ clusters

Cooperative luminescence (CL) occurs in spectral regions in which single ions do not have energy levels. It was first observed more than 40 years ago, and all results reported so far are from a pair of ions. In this work, upconverted CL of three Yb3+ ions was observed in the ultraviolet (UV) region under near-infrared (NIR) excitation. The UV CL intensity showed a cubic dependence on the NIR pump power, whereas the luminescence lifetime was nearly one-third the luminescence lifetime of single Yb3+ ions. The triplet CL (TCL) has a clear spectral structure, in which most emission peaks are consistent with the self-convoluted spectra from single Yb3+ ions. Blue shifts were observed for certain peaks, indicating complex interactions among the excited Yb3+ ions. The probability of the TCL process versus the average distances among three Yb3+ ions was derived via the first- and second-order corrections to the wave functions of lanthanide ions, indicating that the formation of Yb3+ clusters containing closely spaced ions favors the occurrence of the multi-ion interaction processes. Furthermore, the cooperative sensitization of one Gd3+ ion by four excited Yb3+ ions (Yb3+-tetramer) was demonstrated experimentally, which exhibited a novel upconversion mechanism—cluster sensitization. Our results are intriguing for further exploring quantum transitions that simultaneously involve multiple ions. Scientists in China have observed ultraviolet light emission from a cluster of rare-earth Yb3+ ions in a CaF2 matrix. Zhen-Yu Liu and co-workers from Jilin University excited the polycrystalline powders with 978 nm near-infrared laser light. The resulting up-converted emission in the ultraviolet is believed to be due to a phenomenon called co-operative luminescence, whereby multiple Yb3+ ions emit a single shorter-wavelength photon by simultaneous depopulation from their excited states. In this particular case, three Yb3+ ions are thought to be involved — a hypothesis confirmed by low-temperature laser spectroscopy of the sample. This process is interesting because it could lead to light emission at wavelengths that lie outside the absorption and emission bands of single ions.

Intense cooperative upconversion emission in Yb/Er: TeO2–Li2O–WO3 oxyfluoride glass ceramics

Novel oxyfluoride glass ceramics based on Yb3+-doped TeO2–Li2O–WO3–ErF3 (TWLE) were prepared using the two-stage heat-treatment method. The structural characterisation of these materials with X-ray diffraction indicated that crystalline phases of LiYbErF4 nanocrystals grew in the glass ceramics. Upon excitation with a 980nm laser diode the Yb3+ doped (2mol%) TWLE glass-ceramic produced intense blue emission at 487nm, weak green emission at 525nm and 550nm, and red emission at 650nm at room temperature. The mechanism of the blue emission, which is attributed to cooperative upconversion from pairs of excited Yb3+ ions to ground-state Er3+ ions, and the weak red and green emissions, which are attributed to energy transfer from Yb3+ to Er3+ ions, were investigated. The results of a pump-power dependence measurement suggested that the blue cooperative emission is a two-photon process. A rate equation was used to describe the cooperative energy-transfer process among the donor and acceptor ions. The observed results were compared to the behavior of another glass materials that exhibits blue cooperative emission, revealing the considerable advantage of TWLE:2Yb glass ceramics for optical devices.

Nonlinear losses in photoconductive Yb:YAG laser materials: identification of photocarrier properties by non-steady-state photoEMF

We report on the investigation of the photocarrier sign and the excitation dynamics in Yb:YAG at 940 nm excitation wavelength by non-steady-state photo-electromotive force technique. Annealed crystals with 25 and 50 % Yb-doping concentration demonstrate hole conductivity, while 80 % Yb:YAG displays electron conductivity. A characteristic relaxation time of approximately 1 ms is observed, which corresponds to the lifetime of the excited Yb3+-ion.

Multicolor frequency upconversion luminescence in Eu3+/Tb3+/Yb3+-codoped fluorogermanate glass excited at 980 nm

Glasses80GeO3:10PbF2:10CdF2 triply-doped with europium, terbium, and ytterbium phosphors were synthesized and the energy up-conversion luminescence emission properties investigated as a function of NIR excitation power, rare-earth ions content combination, and glass phosphor composition. Multicolor visible luminescence with main emissions peaked around 490, 545, 590, 610, 650, and 700nm was observed when samples were excited by a diode laser at 980nm. The up-conversion excitation mechanism for both Eu3+, and Tb3+ excited-state emitting levels was achieved via phonon-assisted cooperative energy-transfer from pairs of excited Yb3+ ions. White-light emission with CIE-1931 coordinates in the region of low color correlated temperature was obtained for appropriate combination of rare-earth ions content.

Transient absorption in pumped Yb fibers opens a path to photodarkening

We investigated the strong absorption change appearing in ytterbium (Yb)-doped silica simultaneously with Yb3+ excitation and vanishing immediately after pump power switch-off. The transient absorption peaks below 300 nm for all the investigated host glass compositions. It extends at least to 500 nm for samples with aluminum codoping or without any codoping and is therefore supposed to constitute the first step needed to enable photodarkening (PD). Our observations indicate that defect complexes including one Yb3+ ion can be activated stepwise. Firstly, their original absorption spectrum is shifted by the energy of the Yb3+ excitation. Secondly, this transient absorption opens the path to the generation of PD color centers by pump photons or energy transfer from neighboring excited Yb3+ ions. In samples codoped with phosphorous only, we found transient absorption of comparable strength but limited to the wavelength range below 350 nm. Thus, the second step of activation seems to be inhibited, which might be an explanation for the consistently observed low PD effects in this fiber type.

Cooperative processes in Cs2NaYbF6 elpasolite crystals

Spectroscopic and luminescent properties of Yb3+-doped Cs2NaYF6 and stoichiometric Cs2NaYbF6 crystals are studied in the infrared and visible spectral regions. The stoichiometric Cs2NaYbF6 compound demonstrates a visible emission when excited by the laser radiation with the wavelength of about 1μm. The decay time of the emission at the wavelength 481nm is 2.73ms as compared to 5.63ms for the luminescence corresponding to the 5F5/2→5F7/2 transition in the Yb3+ ion. We show that the experimental results do not contradict to both the cooperative luminescence mechanism within Yb3+–Yb3+ pairs and to the cooperative sensitization of trace Tm3+ ions by a pair of excited Yb3+ ions.

Energy transfer processes from Yb3+ to Ln3+ (Ln=Er or Tm) in heavy metal glasses

Heavy metal glasses doubly doped with Yb3+ and Ln3+ ions (Ln=Er or Tm) were studied. Glass host matrices were limited to lead borate glass and lead germanate glass. Efficient resonant (Yb3+-Er3+) and non-resonant (Yb3+-Tm3+) energy transfer was observed for the studied systems. Near-infrared luminescence spectra at 1.53 μm (Er3+) and 1.9 μm (Tm3+) were detected under excitation of Yb3+ by 975 nm diode laser line. They corresponded to 4I13/2→4I15/2 (Er3+) and 3F4→3H6 (Tm3+) transitions of rare earth ions, respectively. The unusual large spectral linewidth nearly close to 110 nm for 4I13/2→4I15/2 transition of Er3+ ions in lead borate glass was obtained, whereas long-lived near-infrared luminescence at 1.53 μm was detected in lead germanate glass. Quite different situation was observed for Yb3+-Tm3+ doubly doped glasses. In contrast to lead borate glass, near-infrared (3F4→3H6) luminescence spectra were registered for Tm3+ ions in lead germanate glasses, only. These phenomena strongly depended on stretching vibrations of glass host, which was confirmed by FT-IR spectroscopy.

Ultralow-threshold laser and blue shift cooperative luminescence in a Yb3+ doped silica microsphere

An experimental investigation on ultralow threshold laser and blue shift cooperative luminescence (CL) in a Yb3+ doped silica microsphere (YDSM) with continuous-wave 976 nm laser diode pumping is reported. The experimental results show that the YDSM emits laser oscillation with ultralow threshold of 2.62 μW, and the laser spectrum is modulated by the microsphere morphology characteristics. In addition, blue emission of YDSM is also observed with the increase of pump power, which is supposed to be generated by CL of excited Yb ion-pairs with the absorption of 976 nm photons and Si-O vibration phonons, and the process is explained with an energy level diagram. This property of the blue shift CL with phonons absorption in the Yb3+doped microcavity makes it attractive for the application of laser cooling based on anti-Stokes fluorescence emission, if the Yb3+doped microcavity made from with low phonon energy host materials.

Abnormal broadband photoluminescence from Yb3+/Mn2+ codoped barium octaborate

Abstract Concentration-dependent anomalous broadband down- and upconversion luminescence of Yb 3+ /Mn 2+ codoped barium octaborate have been demonstrated. Upon ultraviolet (UV) excitation, dual Gaussian emission bands depend on the Mn 2+ concentration located at 550 and 656 nm were respectively ascribed to the Mn 2+ pairs and single Mn 2+ ion. Moreover, abnormal broadband upconversion luminescence at room temperature in BaB 8 O 13 :Yb 3+ , Mn 2+ under near-infrared (NIR) excitation of Yb 3+ at 976 nm was demonstrated by the cooperative sensitization luminescence process. The experimental results could provide new insights into developing lighting and display systems, and biomedical imaging.

Studies on the Optogalvanic Effect and Isotope-Selective Excitation of Ytterbium in a Hollow Cathode Discharge Lamp Using a Pulsed Dye Laser

This paper presents studies on the pulsed optogalvanic effect and isotope-selective excitation of Yb 555.648 nm (0 cm(-1) → 17 992.007 cm(-1)) and 581.067 nm (17 992.007 cm(-1) → 35 196.98 cm(-1)) transitions, in a Yb/Ne hollow cathode lamp. The Yb atoms were excited by narrow linewidth (500-1000 MHz) Rh110 and Rh6G dye based pulsed lasers. Optogalvanic signal inversion for ground state transition at 555.648 nm was observed beyond a hollow cathode discharge current of 8.5 mA, in contrast to normal optogalvanic signal at 581.067 nm up to maximum current of 14 mA. The isotope-selective excitation studies of Yb were carried out by recording Doppler limited optogalvanic signals as a function of dye laser wavelength. For the 581.067 nm transition, three even isotopes, (172)Yb, (174)Yb, and (176)Yb, and one odd isotope, (171)Yb, were clearly resolved. These data were compared with selective isotope excitation by 10 MHz linewidth continuous-wave dye laser. For 555.648 nm transition, isotopes were not clearly resolved, although isotope peaks of low modulation were observed.

Spectroscopy and energy transfer in Nd3 +/Yb3 + codoped chalcohalide glasses

In this work, we report the study of energy transfer between Nd3+ and Yb3+ ions in GeS2–Ga2S3–CsCl chalcohalide glasses at room temperature by using steady-state and time-resolved laser spectroscopy. The study includes absorption, emission, and excitation spectra, as well as lifetime measurements. The presence of Yb3+ emission after excitation in the 4F5/2 level of Nd3+ together with the 4I9/2→4F5/2 and 4I9/2→4F3/2 bands of Nd3+ in the excitation spectra of Yb3+ ions confirm that energy transfer occurs from Nd3+ to Yb3+. The transfer efficiency was investigated from the emission spectra. Back transfer from Yb3+ to Nd3+ was also observed in the emission spectra of the codoped samples after excitation of Yb3+ ions.

Spectral evolution of NIR luminescence in a Yb3+-doped photonic crystal fiber prepared by non-chemical vapor deposition

Silica-based Yb3+-doped glass is prepared by non-chemical vapor deposition. The drawn photonic crystal fiber (PCF) has a strong absorption at 976 nm and emission wavelength of approximately 1 037 nm. The intensity and spectral lineshape of the near infrared (NIR) luminescence of the Yb3+-doped PCF are recorded and discussed in terms of excitation power, excitation wavelength, fiber length, and Yb3+ ion concentration. The emission intensifies as the excitation power and Yb3+ ion concentration increase. The intensity of the shorter wavelength side of the luminescence spectrum decreases as the length of the PCF increases.

Origin of 2.7 μm luminescence and energy transfer process of Er3+: 4I11/2→4I13/2 transition in Er3+/Yb3+ doped germanate glasses

An investigation of spectroscopic property and energy transfer process of Er3+ doped and Er3+/Yb3+ co-doped germanate glasses is presented. The emission cross section of the 4I11/2 → 4I13/2 transition of Er3+ doped germanate glass is calculated to be 1.2 × 10−20 cm2. The microparameter of energy transfer from Yb3+:2 F5/2 to Er3+:4I11/2 is calculated to be 2.74 × 10−39 cm6/s, and that is not phonon dependent in the quasiresonant process. The intensity of the emission around 2.7 μm is enhanced obviously when Er3+ co-doped with Yb3+. The excited-state relaxation process of Er3+ is adequately described by a combination of the Judd-Ofelt model and the energy-gap law. With the exception of 4I13/2 and 4I11/2 levels, multiphonon relaxation is dominant for all excited states, making it possible to efficiently pump the 1.55 μm 4I13/2 → 4I15/2 and 2.7 μm 4I13/2 → 4I11/2 emission by excitation of Yb3+:2F5/2 and Er3+:4I11/2 at 980 nm.

Intense Blue-Green Cooperative Luminescence from Yb3+ Pairs within CaNb2O6 Matrix

An intense and rather broad emission band around 500 nm is observed in Yb3+ doped CaNb2O6 phosphor with near-infrared (NIR) laser excitation. On the basis of measurements of emission spectra, excitation intensity dependence and decay times, we conclude that the visible emission is ascribed to cooperative luminescence, i.e., the emission of one photon due to simultaneous radiative relaxation of a pair of interacting excited Yb3+ ions. The concentration dependence of the Yb3+ cooperative luminescence has been studied. Competition with a nonradiative energy transfer by upconversion process is observed due to the presence of Er3+ and Tm3+ ions as unexpected impurities. Low temperature spectroscopy and lifetime measurements evidence the existence of Yb3+ pairs formed at two types of minor Yb3+ centers which have been identified within CaNb2O6 matrix. The experimental results indicate that the cooperative luminescence mainly directly originates from the minority Yb3+ ion-pair centers while energy transfer from the main center to the minor centers of Yb3+ exists. In addition, cooperative luminescence exhibits remarkable thermal quenching at high temperature.

(Gd,Yb,Tb)PO4 up-conversion nanocrystals for bimodal luminescence–MR imaging

Up-conversion (Gd,Yb,Tb)PO(4) materials and their potential for bimodal imaging have received little attention in the literature. Herein, we report the first study on the up-conversion emission of (Gd,Yb,Tb)PO(4) nanocrystals synthesized via a hydrothermal method at 150 °C. These materials exhibit ultraviolet, blue and green up-conversion emissions upon excitation with a 980 nm continuous wave laser diode. The intensity of the blue-emission band at 479 nm, ascribed to the cooperative up-conversion emission of a pair of excited Yb(3+) ions, depends on the Yb(3+)/Tb(3+) concentration ratio, calcination temperature and particle size. Strong green up-conversion emission of Tb(3+) is observed at 543 nm for the (5)D(4)→(7)F(5) transition. Relaxometry measurements reveal that the nanocrystals are efficient T(2)-weighted (negative) contrast agents which, combined with visible-light emission generated by infrared excitation, affords them considerable potential for being used in bimodal, photoluminescence-magnetic resonance, imaging.