Rare Earth Ion Doping Research Articles

Effect of codoping of Rare Earth ions on Microstructure and Band Gap of Ti0.98A0.01Gd0.01O2 (A: Sm/Eu/Tb) Nanostructures Synthesized by modified hydrothermal method

Sm3+, Eu3+, Tb3+ and Gd3+ ions have been incorporated in anatase TiO2 nanostructures by a hydrothermally modified sol gel method. XRD data analysis revealed the formation of pure anatase phase that crystallizes in the tetragonal crystal symmetry without any secondary phase. FTIR spectra indicate stretching vibrations of bonds in the nanostructures. The absorption peak centered at 568 cm−1 is related to the Ti-O-Ti stretching vibrations. Morphological studies and grain size estimation were performed by SEM measurements. SEM images depict nonuniform distribution of grains with a considerable variation in grain size. EDS measurements ensure chemical compositions in the samples. UV-visible absorption spectroscopy was used to study the optical properties. The doping of rare earth ions (Sm3+, Eu3+, Tb3+) leads to the variation in band gap of TiO2. Photoluminescence (PL) spectra indicate a significant change in the intensity on the doping of rare earth ions.

Combating Concentration Quenching in Upconversion Nanoparticles.

Lanthanide-doped upconversion nanoparticles (UCNPs) are a special class of luminescent nanomaterials that convert multiwavelength near-infrared (NIR) excitation into tunable emissions spanning the deep ultraviolet (UV) to NIR regions. In addition to large anti-Stokes shift, UCNPs also feature a sharp emission bandwidth, long excited-state lifetime, as well as high resistance to optical blinking and photobleaching. Therefore, UCNPs have been identified as promising candidates to solve many challenging problems in fields ranging from biological imaging and therapeutics to photovoltaics and photonics. Nevertheless, the progress of utilizing an upconversion process is being hindered by the limited emission intensity, principally due to low oscillator strength in these nanoparticles. UCNPs essentially resemble the optical characteristics of their bulk counterparts, which take advantage of electronic transition within the 4f configuration of the lanthanide dopants to realize photon energy conversions. In general, a high dopant concentration promotes upconversion luminescence by providing a high density of optical centers to collect and to sustain the energy of the excitation light. However, an increase in dopant concentration induces self-quenching processes that offset the emission gain and may eventually result in attenuation of the overall emission intensity. This phenomenon known as concentration quenching represents a major obstacle to constructing bright UCNPs. In recent years, advances in nanoparticle research have led to the emergence of several strategies for mitigating energy loss at elevated dopant concentrations. In consequence, doping high levels of lanthanide ions in UCNPs has become a viable solution to boosting the emission intensity of photon upconversion. On account of extensive energy exchange interaction in heavily doped UCNPs, the spectrum tunability of photon upconversion is also greatly enhanced. These advances have largely expanded the scope of upconversion research. To provide guidelines for enhancing upconversion through heavy doping, we attempt to review recent advances in the understanding and control of concentration quenching in UCNPs. With significant advancements made in the chemical synthesis, we are now able to exquisitely control the doping of lanthanide ions in various nanoparticles of well-defined size, morphology, and core-shell structure. We show that, by confining energy transfer in nanostructured host materials in conjunction with innovative excitation schemes, concentration quenching of upconversion luminescence is largely alleviated. As a result, unusually high dopant concentrations can be used to construct UCNPs displaying high brightness and large anti-Stokes shift. We demonstrate that the development of heavily doped UCNPs enables advanced bioimaging and photonic applications that can hardly be fulfilled by conventional UCNPs comprising low concentrations of lanthanide dopants.

Polishing characteristics of Nd:YAG ceramics with various Nd-dopant concentrations

Neodymium-doped polycrystalline yttrium aluminum garnet (Nd:YAG) ceramics require nanometer-scale surface roughness when used as laser gain media to minimize light scattering. Variations in grain size and crystallographic orientation can result in uneven material removal between grains and excessive material removal at the grain boundaries, hindering the smoothing of this material. The introduction of rare earth ion dopants, necessary for laser oscillation, can influence these parameters. This paper explores the effects of varying dopant concentration on grain structure and those effects on the polishing characteristics of polycrystalline Nd:YAG ceramics.

An auto-combustion synthesis and luminescence properties of polyhedral YVO4: Ln3+ (Ln = Eu, Sm, Yb/Er, Yb/Tm) microcrystals

Abstract

Enhancing upconversion luminescence of highly doped lanthanide nanoparticles through phase transition delay

Doping of rare earth (RE) ions in a low-phonon-energy host matrix is an effective strategy to enhance the upconversion luminescence (UCL) of lanthanide-doped nanoparticles. However, doping of optically inactive RE ions at high concentrations can cause an undesirable phase transition of the host matrix, with concomitant decrease in luminescence. Herein, we present a phase-transition-delay protocol to effectively preserve the pure orthorhombic phase of a KLu2F7:Yb3+,Er3+ system, even at high RE dopant concentrations. The proposed concept can be realized by incorporating a set of optically inactive RE dopants, i.e., Y3+ or Gd3+, with different ionic radii to replace the Lu3+ ions in the host matrix to overcome the energy barrier of the phase transition. The nanoparticles were synthesized in a high-boiling solvent or at a high reaction temperature. We observed maximal UCL of Er3+ at different Y3+ or Gd3+ dopant concentrations; the optimal Y3+ or Gd3+ concentration at which maximal UCL is observed is 10 mol% for samples prepared by a water-based hydrothermal route, while it is 30 mol% for samples prepared by an oleic acid-based hydrothermal route. Further, this optimal concentration could be increased to as much as 50 mol% by adopting a high reaction temperature. The high doping of Y3+ or Gd3+ can efficiently lead to enhanced upconversion performance of the final materials (as much as 32-fold and 9-fold enhancements in the upconversion intensity and quantum yield, respectively, are achieved). The UCL enhancement is caused by the break-down of the symmetry of lanthanide sites in the crystal lattice induced by Y3+ or Gd3+, which enhances the energy transfer probabilities between Yb3+ and Er3+. Our findings highlight a convenient route to simultaneously tune the phase transition of the host and upconversion output, and this strategy can be applied to other upconversion host materials.

Fabrication of La-Doped Bi2O3 Nanoparticles with Oxygen Vacancies for Improving Photocatalytic Activity

La-doped Bi2O3 were prepared via a simple sol–gel method following a facile low temperature calcination process, and citric acid as an organic complexing agent. La3+ doping could not only create oxygen vacanices (OVs) on the surface of Bi2O3, but also as the efficient scavenger to capture photogenerated electrons. The novel x% La–Bi2O3 photocatalysts exhibited oxidation capacities for degrading azo dye methyl orange (MO) and colorless pollutant phenol, and 2% La–Bi2O3 sample showed the highest photocatalytic activity. The enhanced photocatalytic activity in MO and phenol photo-degradation were attributed to the strong synergistic effects of La3+-doping and oxygen vacancies (OVs), which La3+ ions capture, transfer, and release the photo-generated electrons for conversion from O2 to $$ ^{ \cdot } O_{2}^{ - } $$ to prevent the hot e− of CB to jump into the level of OVs, thereby increase separation efficiencies of photo-generated electrons and holes. The present study may present a new perspective for the utilization of rare earth ion doping to improve the performance of other photocatalytic materials.

Effect of Tm dopant on luminescence, photoelectric properties and electronic structure of In2S3 quantum dots

Doping is an effective method to tune the properties of semiconductor nanomaterials. Particularly rare earth ion doping has attracted increasing attention due to its excellent optical properties. However, the design and synthesis of the indium sulfide (In2S3) quantum dots (QDs) with controllable optical electronic structure remain a challenge. Herein, Tm-doped In2S3 QDs are synthesized using a gas-liquid chemical deposition method. Fluorescence intensity of In2S3: Tm QDs has great enhancement, which can be controlled by regulating doping concentrations of Tm3+ ions. The photoelectric properties of In2S3: Tm QDs are also researched and the results demonstrate enhanced sensitivity to light, short response/recovery times and long-term stability. Furthermore, based on first-principles calculations, the change of electronic structure and enhancement of optical properties in In2S3: Tm QDs are mainly attributed to Tm3+ ions doping. The as-synthesized In2S3 QDs with luminescent and photoelectric properties are expected to have extensive applications in photovoltaic, photoelectric and sensor fields.

An intelligent nanoplatform for imaging-guided photodynamic/photothermal/chemo-therapy based on upconversion nanoparticles and CuS integrated black phosphorus

The strategy of combining imaging and treatment has been shown as a widely studied and promising approach. In this work, we first integrated copper sulfide (CuS) nanoparticles and black phosphorus (BP) nanosheets with strong negative charges via mesoporous silica-coated upconversion nanoparticles (UCNPs). Synergistic treatment of photothermal, photodynamic and chemotherapy can be achieved after loading doxorubicin (DOX). The nanocomposites perform excellent antitumor efficiency under 808 nm near-infrared (NIR) light, and avoid the slightly lower efficiency and limited penetration depth of conventional ultraviolet and visible (UV–vis) light. In this system, the pore size of mesoporous silica and the large specific surface area of BP are advantageous for achieving high DOX loading capacity. Furthermore, the reduction in the red/green (R/G) ratio elicited by DOX release can be employed to determine the extent of DOX release by the fluorescence resonance energy transfer (FRET) process. CT/MR imaging induced by doping of rare earth ions imparts multimode imaging capabilities to nanosystem under 808 nm light irradiation, thereby enabling imaging-guided cancer treatment.

Tuning the Doping of Europium in Gadolinium Borate Microparticles at Mesoscale Toward Efficient Production of Red Phosphors.

The ideal product of rare-earth-doped phosphors should have uniform particle size distribution and homogeneous doping ions in each particle, and therefore, intensified micromixing at mesoscale is highly required. In this article, inspired by the concept of “mesoscience”, we demonstrate the tuning of Eu3+ doping in GdBO3 microparticles at mesoscale by a high-gravity-assisted reactive precipitation-coupled calcination process. The high-gravity environment and tiny droplets generated by the high-gravity rotating packed bed (RPB) reactor lead to significant intensification of mass transfer and micromixing, which are beneficial for the homogeneous doping of Eu3+ in the host material during reactive precipitation in liquid solution. Under excitation at 395 nm, the emission spectra of the Eu3+-doped phosphors exhibit a narrow-band red emission centered at 625 nm and the highest intensity was observed at x = 0.2. The RPB products show higher intensity than that of the control group even when the reaction time was shortened to 1/6. After calculation, the quenching in the sample most likely results from dipole–dipole interactions. The chromaticity coordinates for the RPB sample was measured as (0.598, 0.341) with a quantum yield of up to 78.11%, and the phosphors exhibit good thermal stability at 423 K. The phosphors were used as the luminescent materials for light-emitting diodes (LEDs), and the devices showed good performance. Our preliminary study illustrated that high-gravity-assisted approaches are promising for tuning the doping of rare-earth ions in microparticles at mesoscale toward efficient production of phosphors for LEDs.

Frequency and temperature dependent magnetic properties with structural Rietveld refinement of Co0.25Zn0.75YxFe2−xO4 ferrites

Doping of rare earth (RE) ions can influence the magnetic properties in spinel ferrites, whereas the phase formation plays an important role. Therefore, it is important to choose the RE ions for doping content to get more benefit. In this work, synthesis of Yttrium doped Co-Zn ferrites were carried out by the method of solid state reaction. Co0.25Zn0.75YxFe2−xO4 (CZYF) is the general formula of the studied ferrites where x = 0.00, 0.02, 0.04, 0.06 and 0.08. The structural properties of CZYF ferrites were studied by X-ray diffraction (XRD) technique and further refined by Rietveld method. XRD and Rietveld refinement approved that all the CZYF samples are cubic spinel structure and the lattice parameters were increased with increasing Y content. The variation of grain growth and surface morphology of CZYF samples were studied from SEM images indicated that the average grain size increased from 1.412 µm to 2.341 µm. Frequency dependent magnetic properties (complex permeability, loss factor) were observed in the range of 100 Hz to 120 MHz at 300 K (room temperature). The initial permeability of CZYF ferrites are found to decrease with the increase in Y content. This decrease nature of permeability is related to the increase of porosity and average grain size. At three different temperatures (80 K, 200 K and 300 K), we measured saturation magnetization, coercivity and remanent magnetization. The mentioned properties make CZYF ferrites applicable for use as a soft ferrite.

Preparation and luminescent properties of tunable polychromatic phosphors CaNaB5O9: RE3+(RE = Dy, Eu, Tb)

A series of CaNaB5O9: RE3+ (RE = Dy, Eu, Tb, Tb/Eu, Dy/Eu) phosphors were prepared by the traditional high temperature solid state method. The crystal structure, morphology and luminous properties were characterized by powder X-ray diffraction, scanning electron microscopy and fluorescence spectra, respectively. The influence of rare earth ion doping concentration on the luminescence performance of samples was discussed. The optimal doping concentrations of Dy3+, Eu3+ and Tb3+ were 1 mol%, 15 mol% and 5 mol%, respectively. Under certain wavelength excitation, the samples CaNaB5O9: Dy3+, CaNaB5O9: Eu3+ and CaNaB5O9: Tb3+ can emit white light, red light and green light respectively. Under the near ultraviolet excitation of 369 nm, Ca1-x-yNaB5O9: xTb3+, yEu3+ phosphors can effectively transfer the excitation energy from Tb3+ to Eu3+. The luminous color changes gradually from green to yellow. Under the excitation of 393 nm, the emission spectra of CaNaB5O9: Dy3+, Eu3+ phosphors show the typical transition emission of Dy3+ and Eu3+. The red emission from energy transition of Eu3+ adds red light to the white emission of Dy3+ and decrease the color temperature. The results show that the sample CaNaB5O9: RE3+ (RE = Dy, Eu, Tb) can be the candidates of color-tunable phosphors for W-LEDs.

Structure of nanocrystalline Nd0.5R0.5FeO3 (R=La, Pr, and Sm) intercorrelated with optical, magnetic and thermal properties

Polycrystalline samples of Nd0.5R0.5FeO3 (R = La, Pr and Sm) synthesized by sol-gel combustion method have been investigated for their structural, optical, thermal and magnetic properties. X-ray diffraction in combination with Fourier transform infrared (FTIR) spectra confirm the single-phase orthorhombic structure with Pbnm space group of all the samples. Rietveld refinement employed to determine the bond lengths (Fe–O, R–O) and bond angles (Fe–O–Fe) show a decrease in the bond angle with Sm doping. Transmission electron microscopy (TEM) micrographs reveal the nano-size particles and selected area electron diffraction (SAED) patterns indicate good crystallinity with a uniform distribution of particles throughout the samples. Raman spectra clearly indicate the compressive strain in the Sm doped sample that has been correlated with the structural parameters obtained from Rietveld refinement. The shift in wavenumber is the main cause of change in bond length (Fe–O) and tilt of octahedra due to rare earth ions. The optical bandgap is determined using Tauc's relation from the diffuse reflectance spectra. The variation of specific heat has been investigated with temperature in a broad temperature range. The endothermic peak in specific heat has been correlated with magnetic order. The value of Néel temperature increases in the case of La-doped sample and reduces for the Pr doping. However, the decrease of specific heat in Sm doped sample around 300 °C may be attributed due to the spin reorientation. Magnetic studies at room temperature reveal antiferromagnetic behavior with weak ferromagnetic component due to the canted ordering of Fe3+ spins. Magnetic properties are strongly dependent on the type of rare earth ion as the maximum magnetization (Mm) is enhanced from 0.259 to 0.434 emu/g with the doping of rare earth ions (La, Pr and Sm). The increase in magnetization has been correlated with increased distortion which is evident from the decrease in the bond angle. Exchange bias (EB) effect is observed for all samples as single-phase orthorhombic structure is composed of antiferromagnetic (AFM) and ferromagnetic (FM) phases.

Influence of rare earth addition in cobalt ferrite thin films obtained by pulsed laser deposition

The influence of rare earth (RE = Dy, Gd, Yb) ion doping on the structural, magnetic and optical properties of cobalt ferrite thin films was studied. CoFe2-xRExO4 (x = 0.01; 0.03; 0.05; 0.1; 0.2; 0.3) films were obtained by pulsed laser deposition on silicon substrates. The X-ray diffraction and Raman spectroscopy results on the bulk materials, which were used as targets during deposition, revealed the formation of residual phases as the concentration of RE dopant was increased. However, the annealed thin films presented diffraction lines and vibrational modes corresponding only to cobalt ferrite. A lower crystallinity of the deposited samples was observed when higher RE concentrations were used. Due to the substitution of Fe by RE elements which possess large ionic radii, the lattice parameter of the thin films presented a monotonous increase. The magnetic response of the nanostructures was correlated to the magnetic moment of the RE dopant and to the structural properties of the films. The optical bandgaps derived from the reflectance spectra presented an increasing trend as the Yb and Dy concentrations were augmented.

The ability of GexGa4S96-x chalcogenide glasses dissolving rare earth probed by x-ray photoelectron spectra analysis

We have synthesized the ternary chalcogenide glasses GexGa4S96-x (x = 22.5, 27, 30, 33, 36), and studied the structural evolution of the glasses by the high-resolution x-ray photoelectron spectra (XPS) technique. We decomposed S 2p, Ge 3d and Ga 3d core XPS spectra into different structural units and found that, with increasing Ge content, part of S-Ge(Ga)-S structure changes into (Ge,Ga)-Ge(Ga)-S, and finally Ge(Ga) clusters appear in the chemically stoichiometric and S-poor glasses. The formation of Ge(Ga) clusters in the chemically stoichiometric and S-poor glasses indicates that, only S-rich Ge–Ga–S glasses can be effectively used as hosts for the doping of rare earth ions, in which no Ga clusters exist and the rare earth ions can be uniformly distributed in the glasses to avoid any possible photoluminescence quenching.

Upconversion emission of the GaN nanocrystals doped with rare earth ions

The crystalline powders of GaN doped with pairs of rare earth ions Er3+-Yb3+ or Ho3+-Yb3+, were synthesized with using the combustion and ammonolysis procedures. Spectroscopic properties of the investigated GaN nanosized samples were measured and analyzed. As excitation sources, the laser diodes operating at 808 and 975 nm were used. The upconversion emissions in the visible range were observed for used laser excitations. The upconversion emission properties depend on the synthesis conditions and the concentration ratio of the doped lanthanide ions.

Tunable luminescence and energy transfer properties based on La2O3-P2O5:Dy3+/Tm3+ glasses

The white-LED material Dy3+/Tm3+ co-doped phosphate glass was prepared by a conventional melting method. The energy transfer in the two rare earth ions was supposed by changing the concentration of one doping ion and was further demonstrated by the fluorescence lifetime. The energy level transition mechanism between the rare earth ions was analyzed using the Inokuti–Hirayama theory. There were two kinds of energy transfer mechanisms from the dipole–quadrupole interaction (Dy3+ → Tm3+) and the quadrupole–quadrupole interaction (Tm3+→Dy3+). The luminescence color was tuned from a blue to a near standard white light emission using 350 nm excitation and adjusting the rare earth ion doping ratio. The results show that 15La2O3-85P2O5:xDy2O3-yTm2O3 glass is a promising UV-excited white photodiode material.

Perovskite sensitized erbium doped TiO2 photoanode solar cells with enhanced photovoltaic performance

The strategy of ion doping in metal oxide is generally used to enhance the photoanode film feature, attain a suitable energy band and enhance carrier mobility. Here, a rare earth element erbium was doped into TiO2 electron transport layer (ETL) by adding erbium trinitrate into the titanium precursor solution. In the present investigation, an attempt has been made to fabricate perovskite sensitized erbium doped TiO2 nanoparticle (Er3+@TNPs) photoanode solar cell with different hole transport materials (HTMs) and graphite coated counter electrode. The perovskite sensitized solar cell (PSSC) built with CH3NH3SnI3 sensitized Er3+@TNPs photoanode and spiro-MeOTAD HTM shows an impressive photovoltaic performance had the power conversion efficiency (PCE) of 11.54% when compared to the undoped TiO2 photoanode PSSC. The results of this investigation indicate that the rare earth ion doping could be a promising method for producing effective ETL and enhanced performance PSSCs.

Structure and properties of non-alkali aluminoborosilicate glass containing RE (RE = La, Ce, Nd, Dy, Y, Yb) oxides

Network connectivity, physical and chemical properties of non-alkali aluminoborosilicate glasses doped with 1 mol% rare earth (RE) oxides (La2O3, CeO2, Nd2O3, Dy2O3, Y2O3 and Yb2O3) were investigated. The Gaussian fitting results of 29Si MAS NMR showed that the relative concentration of Q4 in the network structure increased and Q3 decreased with RE-doping except the glass doped with Nd2O3. The glass doped with Yb2O3 displayed highest relative concentration of Q4 ~63.4%, indicating a highest degree of network connectivity. It is associated with the highest cation field strength (CFS) of Yb3+ ion among the doping RE ions. The enhancement of network connectivity resulted the improvements of Vicker's hardness, dielectric constants, glass stain point (Tst), HF- and NaOH-resistance. The glass doped with Nd2O3 contained only 43.3% Q4 in the network structure, and the fraction is even smaller than that of glass without RE oxides. The loose structure is probably attributed to the small dielectric constant of glass doped with Nd2O3, which is the only sample with the smaller dielectric constant than the glass without RE-doping.

Trap level analysis of Ce3+ and Sm3+ in Li6Y(BO3)3

Abstract The polycrystalline compounds of Li6Y(BO3)3: Ce3+ and Sm3+ co-doped polycrystalline samples were prepared by using standard solid state reaction method. The energy levels of the doped lanthanide ions (Ce3+ and Sm3+) in the borate host materials were investigated by Thermoluminescence (TL) glow peak analysis. The co-doped samples, exhibits the TL peak at higher temperature region around 511 K whereas the Ce3+ individually doped sample has peak around 433 K. The X-ray excited emission spectra were carried out for all the prepared samples and found the characteristic emission bands. The trap depths (E) were calculated by using several standard methods, namely peak shape method or chen's (PS), variable heating rate (VHR), initial rise (IR) and computerized glow curve deconvolution (CGCD). The mean activation energy of the co-doped samples found to be 1.21 (0.07±) eV and the frequency factor around 1.38 × 1011 Sec−1. The calculated trap depths and the predicted energy level values were compared and found in good agreement. This primarily results suggest that the energy level scheme can help in the development of new TL materials suitable in dosimetry.

Upconversion luminescence of Ca2Gd8(SiO4)6O2:Yb3+-Tm3+-Tb3+/Eu3+ phosphors for optical temperature sensing

In order to develop new upconversion (UC) phosphors for optical temperature sensors, a series of Yb3+-Tm3+-Tb3+/Eu3+ doped Ca2Gd8(SiO4)6O2 (CGS) samples were designed by solid-state reaction method. The phase purity was examined by XRD patterns, which revealed that the obtained samples are all single-phase in spite of the rare earth (RE) ions doping. Upon 980 nm excitation, the emission peaks of all the doped luminescent ions (Tm3+, Tb3+ and Eu3+) have been observed, and the energy transfer processes among the RE ions in the UC luminescence were discussed with the help of the energy level diagram and decay curves. The competitive absorption between Tm3+ and Tb3+/Eu3+ from Yb3+ was proposed to interpret the sharp decrease of Tm3+ emission intensity. The temperature sensing behavior was evaluated by measuring the temperature-dependent UC luminescence of the typical CGS:10%Yb3+,0.2%Tm3+,10%Tb3+,1.25%Eu3+ phosphor. It has been found that the fluorescence intensity ratio (FIR) technique by employing ITb/IEu and ITb/ITm can generate high absolute sensitivity, but the relative sensitivity still needs further improvement compared with some other phosphors doped with Er3+/Ho3+/Tm3+.