Rare Earth Ion Doping Research Articles

A synergetic effect of ytterbium-doping and ammoniation on enhancing UV and visible photocatalytic activities of TiO2

A synergetic effect of rare earth (Yb) ion doping and ammoniation on the enhancements of both ultraviolet and visible photocatalytic activities of TiO2 is reported. It is found that ammoniation can dope both nitrogen and hydrogen ions for bandgap narrowing and dangling bond passivation, respectively. Meanwhile, the Yb-doping results in the formation of defective bands that are close to the conduction band minimum, and have strong electron capture abilities to prevent recombination of photogenerated electrons and holes. The synergism of the two effects of Yb doping and ammoniation leads to a significant enhancement of both ultraviolet and visible photocatalysis.

Study of the structural and luminescent properties of Ce3+ and Eu3+ co-doped YAG synthesized by solid state reaction

In this paper, yttrium aluminium garnet (YAG) nano-phosphors are single or co-doped with Ce3+ and Eu3+ rare earth ions in different concentrations. The precursors were prepared by solid state reactions in repeated heating cycles from 1300 to 1600 °C. The crystalline phase was confirmed by an X-ray powder diffraction (XRD) analysis. The rare earth dopant ions were successfully integrated into the YAG host lattice without changing the original structure. The cubic phase of the synthesized phosphors was confirmed by Rietveld refinement. The microstructure and composition of the pure and doped YAG samples were studied in detail using TEM, HRTEM, and EDX elemental composition analyses. The photoluminescence properties of the YAG:xCe3+ (x = 0.01, 0.05, 0.07, 0.09) and YAG:0.05Ce3+, xEu3+ (x = 0.01, 0.02, 0.03, 0.04, 0.05) phosphors were also investigated in detail. The obtained optimal doping molar concentrations of the Ce3+ and the Eu3+ions were 0.07 and 0.02 mol%, respectively. The YAG:xCe3+ exhibited a typical 5d-4f emission broadband with a maximum peak located at 543 nm. We detected a variation of the Ce3+ emission intensity with varying Eu3+ concentration, which may be due to the energy transfer from Ce3+ to Eu3+. The optimum CIE chromaticity coordinates (x, y) of YAG:0.07Ce3+ and YAG:0.05Ce3+, xEu3+[x = 1%], were (0.310, 0.345) and (0.3243, 0.3730), respectively, which were close to the NTSC standard values. The CCT values indicated that for the concentration of Eu3+ (1%), the white light was daylight to cool daylight (5485–6847 K), and for the concentration of Eu3+ (2%), the white light was cool white to daylight (4797–5112 K).

Efficient organic solar cells employing ytterbium ion-doped zinc oxide as cathode transporting layer

Abstract Rare earth ions possess highly conductive, magnetic, electrochemical and luminescent properties, multiple valence electrons and long lifetime of excited state, thus could be alternatives as dopant to tune and promote the cathode interlayer property in solar cells. In this work, we study the modification of cathode interlayer by rare earth ion doping, based on the model of Yb doped ZnO by sol-gel method. A relative low doping concentration (below 1%) can improve the electron transport of ZnO and the solar cell performance. This is also confirmed by the obtained photocurrent density, excitons generation rate and electron mobility of device. The best PCE 11.04% (with VOC 0.940 V, JSC 16.58 mW cm−2, FF 70.7%) is achieved with 0.5% Yb doping, based on PBDB-T:IT-M active layer, compared to the reference PCE of 10.19% with pure ZnO ETL. While with concentration over 1%, the Yb doping decreases the device performance.

Enhanced persistent luminescence of Li2ZnGeO4 host by rare-earth ions (Pr3+, Nd3+ and Gd3+) doping

The blue emitting long afterglow phosphor (LAG) Li2ZnGeO4, Li2ZnGeO4:Nd3+, Li2ZnGeO4:Pr3+, and Li2ZnGeO4:Gd3+ were synthesized via traditional high temperature solid-state reaction in air atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectroscope (PL), luminescence decay, long afterglow spectroscope (LAS) and thermal luminescence spectroscope (TSL) were utilized to characterize and analyze the physical properties of the synthesized phosphors. All phosphor samples present bright blue emission with different intensity under a 254 nm UV lamp. The photoluminescence properties revealed the rare earth ionic (Nd3+, Pr3+ and Gd3+) doping enhanced the luminescence intensity of the host emission and did not change profiles of emission spectra. Further, luminescence decay study showed that the luminescence lifetime of Li2ZnGeO4:R3+ (R = Nd, Pr, Gd) phosphors was increased, indicating energy transform occurred in the processes. After light source was removed, all phosphor sample show evident triple exponential decay behavior. Thermal simulated luminescence study indicated that persistence afterglow of Li2ZnGeO4:Nd3+, Li2ZnGeO4:Pr3+, and Li2ZnGeO4:Gd3+ phosphors were originated from suitable electron or hole traps resulted from rare earth ions (Nd3+, Pr3+ and Gd3+) doping in the Li2ZnGeO4 host.

Broadband, White Light Emission from Doped and Undoped Insulators

We present data on broadband, white light emission from insulating hosts under intense excitation in the near infrared in host materials that are undoped, partially-doped with rare earth ions, and that contain stoichiometric concentrations of rare earth ions. Much of the emission is found to have a blackbody-like structure in the visible and near infrared region. The origin of the emission as from a blackbody is also supported by the temporal characteristics of the emission in response to turning on and off the laser, and also by the dependence of the air pressure in the chamber. However, some of the data presented cannot be explained by blackbody emission alone, so other processes are proposed to explain the observed spectra. The role of the rare earth ion dopants in enhancing the broadband emission is also considered.

Growth and lasing of single crystal YAG fibers with different Ho3+ concentrations

A method to grow single crystal (SC) yttrium aluminum garnet (YAG) fibers with varied rare-earth ion dopant concentration has been proposed. Crystalline holmium aluminum garnet (HoAG), prepared via sol-gel process, was dip-coated on to previously grown SC YAG fibers. The HoAG coated SC YAG fiber preforms were re-grown to a smaller diameter using the laser heated pedestal growth (LHPG) technique. The final dopant concentration of the re-grown SC fiber was varied by changing the number of HoAG coatings on the preform. 120 μm diameter SC Ho:YAG fibers with four different dopant concentrations were grown. Lasing was demonstrated at 2.09 μm for these fibers. A maximum of 58.5% optical-to-optical slope efficiency was obtained.

Covering the optical spectrum through different rare-earth ion-doping of YAG nanospheres produced by rapid microwave synthesis

In this work, YAG:RE3+ (RE = Pr3+, Tm3+, Tb3+, Ce3+, Eu3+, Nd3+, and Er3+;Yb3+) luminescent nanospheres with tunable photoluminescence (PL) emission were prepared by using fast and energy-saving microwave-assisted synthesis (MWAS). The nanopowders were post-annealed at 1100°C for 3h to obtain nanocrystalline phosphors. X-ray diffraction (XRD) analysis confirmed the presence of nanocrystals that were well indexed to the cubic YAG phase. Surface chemical groups were detected using Fourier transform infrared spectroscopy (FTIR). Transmission electron microscopy (TEM) showed that the synthesized samples consist of nanospheres with an average size of ~ 110nm. The effect of aluminum precursors on the morphology of synthesized nanoparticles is discussed. The produced nanophosphors showed strong emission at different wavelengths (ultraviolet, visible and near-infrared) corresponding to different RE3+ ions. Altogether, the merits of spherical morphology and PL emission at various wavelengths endow rare-earth-doped YAG nanoparticles with suitable characteristic for potential applications in the field of nanomedicine (e.g., bioimaging and nanoscintillators), light display systems, optoelectronic devices, and lasers.

Influence of rare earth ion doping (Ce and Dy) on electrical and magnetic properties of cobalt ferrites

Ce and Dy substituted Cobalt ferrites with the chemical composition CoCexDyxFe2-2xO4 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were synthesized through the chemical route, citrate-gel auto-combustion method. The structural characterization was carried out with the help of XRD Rieveld analysis, SEM and EDAX analysis. Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. SEM and EDAX results show that the particles are homogeneous with slight agglomeration without any impurity pickup. The effect of RE ion doping (Ce and Dy) on the dielectric, magnetic and impedance studies was systematically investigated by LCR meter, Vibrating Sample Magnetometer and Impedance analyzer respectively at room temperature in the frequency range of 10 Hz–10 MHz. Various dielectric parameters viz., dielectric constant, dielectric loss and ac conductivity were measured. The dielectric constant of all the ferrite compositions shows normal dielectric dispersion of ferrites with frequency. Impedance analysis confirms that the conduction in present ferrites is majorly due to the grain boundary mechanism. Ferrite sample with x = 0.03 show high dielectric constant, low dielectric loss and hence can be utilized in high frequency electromagnetic devices. Magnetization measurements indicate that with increase in Ce and Dy content in cobalt ferrites, the magnetization values decreased and coercivity has increased.

Research on the photoluminescence and up-conversion luminescence properties of Y2Mo4O15: Yb, Ho under 454 and 980 nm excitation

Y1.8-xYb0.2HoxMo4O15 (x=0.005, 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64) phosphors were synthesised at 700°C by using a solid-state reaction method. The samples were characterised by X-ray diffraction, diffuse reflectance spectra, photoluminescence and up-conversion emission spectra. The photoluminescence spectra of Y2Mo4O15:Yb, Ho shows extremely strong green down-shift luminescence corresponding to the 5F4, 5S2→5I8 transition of Ho3+ ions with Ig/Ir>20 under 454nm excitation. While at 980nm excitation, Y2Mo4O15:Yb, Ho sample exhibits unusual red up-conversion luminescence along with a very weak green emission (Ir/Ig=6.4), which is resulted from the severe non-radiative relaxation (5I6→5I7) process due to the very short decay time of 5I6 states of Ho3+ ions. The mechanism of down-shift luminescence is the electrical dipole – dipole transitions. The quenching concentration for down-shift luminescence is higher than that for up-conversion luminescence, which results from the effects of different luminescence processes and large distance between doped rare earth ions in Y2Mo4O15. The different luminescence mechanism and color performance are also studied.

Upconversion emission and phase transformation study in Yb3+/Er3+ doped SrTiO3 ceramics

ABSTRACTHerein, we report luminescence studies on solid state route prepared SrTiO3:Yb3+/Er3+ ceramic. The SrTiO3 has been turned into a multifunctional material which is ferroelectric in nature via doping of lanthanide ions (0.5 mol% Er3+/2.0 mol% Yb3+). Upconversion enhancement emission of SrTiO3:Yb3+/Er3+ perovskite ceramic has been studied using 980 nm laser excitation with respect to different annealing temperatures. The variation of dielectric constant with annealing temperature has shown well-fashioned pattern and is explained. Furthermore, the present ceramic could be useful for solar cell concentrators, microwave assisted resonators and display devices applications.

Enhanced Performance for Planar Perovskite Solar Cells with Samarium-Doped TiO2 Compact Electron Transport Layers

The tactics of ion doping in metal oxide is normally used to improve the film quality, achieve an appropriate energy band, and enhance carrier mobility. Here, a rare earth element (samarium) was doped into TiO2 compact electron transport layers (ETLs) by adding samarium trinitrate into the titanium precursor solution. The results show that perovskite solar cells (PSCs) with Sm-doped TiO2 exhibit 10.3% enhancement with a power conversion efficiency (PCE) of 14.10%, compared to nondoped devices. It is found that Sm doping can upward shift the Fermi energy level of the ETLs, increase the carrier transport ability, and inhibit the carrier recombination. The results indicate that rare earth ion doping could be a promising method for producing effective ETLs and high performance PSCs.

Probing the Influence of Disorder on Lanthanide Luminescence Using Eu-Doped LaPO4 Nanoparticles.

Lanthanide-doped nanocrystals (NCs) differ from their bulk counterparts due to their large surface to volume ratio. It is generally assumed that the optical properties are not affected by size effects as electronic transitions occur within the well-shielded 4f shell of the lanthanide dopant ions. However, defects and disorder in the surface layer can affect the luminescence properties. Trivalent europium is a suitable ion to investigate the subtle influence of the surface, because of its characteristic luminescence and high sensitivity to the local environment. Here, we investigate the influence of disorder in NCs on the optical properties of lanthanide dopants by studying the inhomogeneous linewidth, emission intensity ratios, and luminescence decay curves for LaPO4:Eu3+ samples of different sizes (4 nm to bulk) and core–shell configurations (core, core–isocrystalline shell, and core–silica shell). We show that the emission linewidths increase strongly for NCs. The ratio of the intensities of the forced electric dipole (ED) and magnetic dipole (MD) transitions, a measure for the local symmetry distortion around Eu3+ ions, is higher for samples with a large fraction of Eu3+ ions close to the surface. Finally, we present luminescence decay curves revealing an increased nonradiative decay rate for Eu3+ in NCs. The effects are strongest in core and core–silica shell NCs and can be reduced by growth of an isocrystalline LaPO4 shell. The present systematic study provides quantitative insight into the role of surface disorder on the optical properties of lanthanide-doped NCs. These insights are important in emerging applications of lanthanide-doped nanocrystals.

A Selective Cation Exchange Strategy for the Synthesis of Colloidal Yb3+-Doped Chalcogenide Nanocrystals with Strong Broadband Visible Absorption and Long-Lived Near-Infrared Emission.

Doping lanthanide ions into colloidal semiconductor nanocrystals is a promising strategy for combining their sharp and efficient 4f-4f emission with the strong broadband absorption and low-phonon-energy crystalline environment of semiconductors to make new solution-processable spectral-conversion nanophosphors, but synthesis of this class of materials has proven extraordinarily challenging because of fundamental chemical incompatibilities between lanthanides and most intermediate-gap semiconductors. Here, we present a new strategy for accessing lanthanide-doped visible-light-absorbing semiconductor nanocrystals by demonstrating selective cation exchange to convert precursor Yb3+-doped NaInS2 nanocrystals into Yb3+-doped PbIn2S4 nanocrystals. Excitation spectra and time-resolved photoluminescence measurements confirm that Yb3+ is both incorporated within the PbIn2S4 nanocrystals and sensitized by visible-light photoexcitation of these nanocrystals. This combination of strong broadband visible absorption, sharp near-infrared emission, and long (>400 μs) emission lifetimes in a colloidal nanocrystal system opens promising new opportunities for both fundamental-science and next-generation spectral-conversion applications such as luminescent solar concentrators.

Adjustable multicolor up-energy conversion in light-luminesce in Tb3+/Tm3+/Yb3+ co-doped oxyfluorifFde glass-ceramics containing Ba2LaF7 nanocrystals

Transparent oxyfluoride glasses with highly efficient up-energy conversion (UEC) luminescence were developed in the 45SiO2-15Al2O3-12Na2CO3-21BaF2-7LaF3-xTbF3-yTmF3-zYbF3 composition (in mol%), and structural investigation by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of face-centered cubic Ba2LaF7 nanocrystals. The colors of UEC luminescences could be tuned easily by adjusting the concentration of doped rare earth ions and the excitation power of laser simultaneously. The relationship between the emission intensity of Tb3+/Tm3+/Yb3+ co-doped oxyfluoride glass-ceramics and the excitation pump power revealed that three-photon and two-photon absorptions predominated in the conversion process from the infrared into blue and red luminescences, respectively. A novel UEC mechanism of red emission from Tm3+ was proposed, energy transfers from Yb3+ to Tm3+ and Tb3+ and from Tm3+ to Tb3+ were evidenced. The possible mechanism responsible for the color variation of UEC in Tb3+/Tm3+/Yb3+ co-doped was discussed.

Mechanistic insights into tunable luminescence and persistent luminescence of the full-color-emitting BCNO phosphors

Boron carbon oxynitride (BCNO) phosphors can exhibit remarkable tunable emission colors and greenish persistent luminescence without the assistant of rare-earth ion dopants. However, the photoluminescent and persistent luminescence (PL) mechanisms of BCNO are still not fully understood. In this work, we attempt to reveal distinct photoluminescent and PL mechanism of BCNO based on the first-principles computation. Our results show that the tunable emission of BCNO stems from the carbon quantum dots (CQDs) embedded in the host BN lattice rather than originally expected from isolated carbon impurity. The embedded CQDs can emit light with size-dependent wavelength (color). Furthermore, oxygen ions chemisorbed at the edge of BCNO can passivate the dangling bonds, and thereby enhance BCNO's quantum efficiency. The PL mechanism can thus be attributed to the defect levels within the band gap, induced by CQDs. This mechanism is distinctly different from the conventional PL mechanism for the rare-earth-metal doped aluminate phosphors [Chem. Mater.2015, 27, 2195–2202]. The obtained new insights into the luminescent and PL mechanisms of BCNO will not only benefit engineering novel optical materials with improved PL properties, but also promote future R&D efforts in exploiting broader application opportunities for the BCNO family phosphors.

Photoluminescence and afterglow behavior of Tb3+ activated Li2SrSiO4 phosphor

A green emitting long afterglow phosphor Li2SrSiO4:Tb3+ was obtained via a conventional high temperature solid-state reaction in air atmosphere. X-ray diffraction (XRD), photoluminescence spectroscope (PLS), long afterglow spectroscope (LAS) and thermal luminescence spectroscope (TLS) were performed to characterize the physical properties of the phosphors. Typical 5D4-7Fj transitions of Tb3+ ions were detected by PL spectra, corresponding to CIE chromaticity coordinates of x=0.3161, y=0.5472. An optimal concentration of Tb3+ in the substrate was determined to be 1%. The Li2SrSiO4:Tb3+ phosphors showed a typical afterglow behavior when the UV source was switched off. A typical triple exponential decay behavior was confirmed after fitting the experimental data. Thermal simulated luminescence study further indicated that the afterglow behavior of Li2SrSiO4:Tb3+ phosphors was generated by the recombination of electrons with the holes resulted from the doping of rare-earth ions (Tb3+) in Li2SrSiO4 host. The long afterglow luminescence mechanism of Li2SrSiO4:Tb3+ is illustrated and discussed in details on the basis of the experimental results.

Preparation, upconversion luminescence, and solid-state NMR studies of water-soluble hexagonal NaScF4:Yb/Er microcrystals

Water-soluble hexagonal NaScF4:Yb/Er upconversion microcrystals (UCMCs) were synthesized using the hydrothermal method. The upconversion photoluminescence properties of NaScF4:xYb/2%Er microcrystals (x = 4–20%) were characterized under a 980-nm-wavelength laser excitation. The dependence of red/green (R/G) ratio on the concentration of Yb3+ ions was investigated. The local environments of dopant ions (Yb3+, Er3+) in NaScF4 were studied using multiple solid-state nuclear magnetic resonance (NMR) techniques. The 19F single pulse and 19F{23Na} and 19F{45Sc} rotational echo double resonance (REDOR) techniques proved that the dopant rare-earth ions (Yb3+, Er3+) preferred to substitute Na+ rather than Sc3+ ions. Such solid-state NMR techniques provide a novel approach to study new phosphors.

Red-emitting enhancement of Bi 4 Si 3 O 12 :Sm 3+ phosphor by Pr 3+ co-doping for White LEDs application

Abstract In this account, Bi4Si3O12:Sm3+ and (Bi4Si3O12:Sm3+, Pr3+) red phosphors were prepared by solution combustion method fueled by citric acid at 900 °C for 1 h. The effects of co-doping Pr3+ ions on red emission properties of Bi4Si3O12:Sm3+ phosphors, as well as the mechanism of interaction between Sm3+ and Pr3+ ions were investigated by various methods. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) revealed that smaller amounts of doped rare earth ions did not change the crystal structure and particle morphology of the phosphors. The photoluminescence spectroscopy (PL) indicated that shape and position of the emission peaks of (Bi4Si3O12:Sm3+, Pr3+) phosphors excited at λex=403 nm were similar to those of Bi4Si3O12:Sm3+ phosphors. The strongest emission peak was recorded at 607 nm, which was attributed to the 4G5/2→6H7/2 transition of the Sm3+ ion. The photoluminescence intensities of Bi4Si3O12:Sm3+ phosphors were significantly improved by co-doping with Pr3+ ions and were maximized at Sm3+ and Pr3+ ions doping concentrations of 4 mol% and 0.1 mol%, respectively. The characteristic peaks of Sm3+ ions were displayed in the emission spectra of (Bi4Si3O12:Sm3+, Pr3+) phosphors excited at respectively λex=443 nm and λex=481 nm (Pr:3H4→3P2, 3H4→3P0). This indicated the existence of Pr3+→Sm3+ energy transfer in (Bi4Si3O12:Sm3+, Pr3+) phosphors.

The role of dysprosium ions on the physical and optical properties of lithium-borosulfophosphate glasses

Achieving outstanding physical and optical properties of borosulfophosphate glasses via controlled doping of rare earth ions is the key issue in the fabrication of new and highly-efficient glass material for diverse optical applications. Thus, the effect of replacing P2O5 by Dy2O3 on the physical and optical properties of Dy[Formula: see text]-doped lithium-borosulfophosphate glasses with chemical composition of 15Li2O–30B2O3–15SO3–[Formula: see text]P2O5–[Formula: see text]Dy2O3 (where 0.0 mol.% [Formula: see text] mol.%) has been investigated. The glass samples were synthesized from high-purity raw materials via convectional melt-quenching technique and characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), density and UV–vis–NIR absorption measurements. The amorphous nature of the prepared glass samples was confirmed by XRD patterns whereas the EDX spectrum depicts elemental traces of O, C, B, S, P and Dy. The physical parameters such as density, refractive index, molar volume, polaron radius and field strength were found to vary nonlinearly with increasing Dy2O3 concentration. UV–vis–NIR absorption spectra revealed seven absorption bands with most dominant peak at 1269 nm (6H[Formula: see text]F[Formula: see text]H[Formula: see text]). From the optical absorption spectra, the optical bandgap and Urbach’s energy have been determined and are related with the structural changes occurring in these glasses with increase in Dy2O3 content. Meanwhile, the bonding parameters ([Formula: see text]) evaluated from the optical absorption spectra were found to be ionic in nature. The superior features exhibited by the current glasses nominate them as potential candidate for nonlinear optical applications.

Doping of RE ions in the 2D ZnO layered system to achieve low-dimensional upconverted persistent luminescence based on asymmetric doping in ZnO systems.

Herein, we dope a low-dimensional ZnO system with a wide range of rare earth (RE) ions. Through systematic calculations, the dopable range of all ZnO systems was found to be asymmetrical, which accounts for the difficulty in achieving p-type doping. Low-dimensional ZnO systems, similar to 2D graphene-like nanosheets, have a wider doping limit. Thus, 2D ZnO is a promising candidate to achieve a wider doping range in ZnO. To further examine energy transfer in upconversion luminescence, the excited states of all lanthanide (Ln) elements in both the Ln2+ and Ln3+ ionic state in the bulk ZnO lattice were extensively studied. The probability of mixed valences of the Ln dopant ions occurring in ZnO was discussed, along with the analysis of the relative oscillator strengths. At the Ln2+ states, the heavy lanthanide elements usually dominated the energy transmission channel at high energy, the medium lanthanide elements mostly occupied the middle range of the optical fundamental gap, and the light lanthanide elements were widely spread over the optical band gap as well as the conduction band range. However, Ln3+ ions, as the sensitizing dopant, have reduced energy barriers for excited state absorption, showing wider energy transfer channels that are evenly distributed within 3.0 eV, which is lower than the conduction band edge absorption in Ln2+. Meanwhile, each energy level has an obviously stronger oscillator strength, indicating a larger probability for excitation and energy transport between the inter-levels. Thus, in physicochemical and biological terms, trivalent Ln doping follows the removal of apical dominance concept, contributing more flexible energy transfer within the biological window for in vivo imaging or other related optoelectronic devices.