Distribution Of Dopant Ions Research Articles

Growth, Optical, and Laser Properties of Large‐Sized Cr,Nd:Y3Al5O12 Crystal

AbstractThe growth and characterization of Cr,Nd:Y3Al5O12 (YAG) crystal are reported. By improving the synthesis and sintering processes of polycrystalline materials, as well as the temperature gradient and annealing atmosphere, a high quality crystal with size of ϕ30 mm × 110 mm is obtained by using the Czochralski technique. After measuring the concentrations of dopant Cr3+ and Nd3+ within the different parts of the grown crystal, it is found that the distribution of dopant ions is uniform throughout the crystal. The fluorescence spectra of Cr,Nd:YAG crystal exhibit intense emissions at 1064 nm under excitations of 808 and 450 nm. The fluorescence lifetime of Nd: 4F3/2 level is obtained to be 234.2 µs. The maximum average output power reaches 7.87 W with a slope efficiency of 31.2% for near‐infrared laser at 1063.9 nm. The above results indicate that Cr,Nd:YAG crystal is a promising gain media for all‐solid state lasers.

Lanthanide-Based Nanosensors: Refining Nanoparticle Responsiveness for Single Particle Imaging of Stimuli.

Lanthanide nanoparticles (LNPs) are promising sensors of chemical, mechanical, and temperature changes; they combine the narrow-spectral emission and long-lived excited states of individual lanthanide ions with the high spatial resolution and controlled energy transfer of nanocrystalline architectures. Despite considerable progress in optimizing LNP brightness and responsiveness for dynamic sensing, detection of stimuli with a spatial resolution approaching that of individual nanoparticles remains an outstanding challenge. Here, we highlight the existing capabilities and outstanding challenges of LNP sensors, en-route to nanometer-scale, single particle sensor resolution. First, we summarize LNP sensor read-outs, including changes in emission wavelength, lifetime, intensity, and spectral ratiometric values that arise from modified energy transfer networks within nanoparticles. Then, we describe the origins of LNP sensor imprecision, including sensitivity to competing conditions, interparticle heterogeneities, such as the concentration and distribution of dopant ions, and measurement noise. Motivated by these sources of signal variance, we describe synthesis characterization feedback loops to inform and improve sensor precision, and introduce noise-equivalent sensitivity as a figure of merit of LNP sensors. Finally, we project the magnitudes of chemical and pressure stimulus resolution achievable with single LNPs at nanoscale resolution. Our perspective provides a roadmap for translating ensemble LNP sensing capabilities to the single particle level, enabling nanometer-scale sensing in biology, medicine, and sustainability.

Graded‐Index Ytterbium‐Doped Optical Fiber Fabricated through Vapor Phase Chelate Delivery Technique

Herein, the fabrication of ytterbium‐doped graded refractive‐index few‐mode fiber (GRIN‐FMF) is described for the first time following a vapor phase chelate delivery technique. Investigation is carried out to find out the best possible approach to fabricate the preform. The optimization of the process steps along with composition and associated process parameters leads to a parabolic refractive‐index profile with a profile parameter of 2 in the developed fiber. A large core of 30 μm diameter and a low numerical aperture (NA) of 0.08 with graded distribution of dopant ions is achieved with a good repeatability. Amplification gain of more than 20 dB with good beam quality for pulses with kW peak power without any distortion in temporal, spectral, and spatial profile proves the potential of the fiber for many promising applications.

Determination of host and dopant ion distribution in Mg2Si1−x Sn x thermoelectric materials by electron channelling

Determination of host and dopant ion distribution in Mg₂Si_1−<i>x</i>Sn_<i>x</i> thermoelectric materials by electron channelling

Perceiving impressive optical properties of ternary SiO2-TiO2-ZrO2:Eu3+ sol-gel glasses with high reluctance for concentration quenching: An experimental approach

Eu3+-doped ternary SiO2-TiO2-ZrO2 glasses were prepared through a non-hydrolytic sol-gel process. Fourier transform infrared spectroscopy was employed to identify the vibrational modes present in the ternary glass. The phonon energies were calculated using excitation spectrum and complemented well with the vibrational modes in the Raman spectrum. Photoluminescence spectrum was used to assess the luminescent augmentation. The uniform distribution of dopant ions in the as prepared ternary glass aided in achieving a comparatively unmatched doping concentration of Eu3+ion (17.5wt%) without luminescence quenching and it can be attributed to reduced cluster formation. High concentration of rare earth ion incorporation leads to intense and tunable emission with higher brightness. Excellent color purity of the emission by means of CIE color gamut for the red color was observed, which is close to the National Television Standard Committee (NTSC) value. Theoretical investigations of the photophysical parameters and radiative decay time were carried out with Judd-Ofelt analysis. The double exponentially fitted decay curve gave a satisfactory experimental lifetime. These results indicate that tailor made europium doped ternary SiO2-TiO2-ZrO2 glasses have potential applications in the areas of photonic devices as well as biological sensors because of its intense tunable and efficient emission, high purity, and low toxicity.

Distribution of dopant ions around poly(3,4-ethylenedioxythiophene) chains: a theoretical study.

The effect of counterions and multiple polymer chains on the properties and structure of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with ClO4- has been examined using density functional theory (DFT) calculations with periodic boundary conditions (PBCs). Calculations on a one-dimensional periodic model with four explicit polymer repeat units and two ClO4- molecules indicate that the latter are separated as much as possible, with the salt structure and band gap obtained from such ClO4- distribution being in excellent agreement with those determined experimentally. On the other hand, DFT calculations on periodic models that include two chains indicate that neighboring PEDOT chains are shifted along the molecular axis by a half of the repeat unit length, with dopant ions intercalated between the polymer molecules acting as cement. In order to support these structural features, classical molecular dynamics (MD) simulations have been performed on a multiphasic system consisting of 69 explicit PEDOT chains anchored onto a steel surface, explicit ClO4- anions embedded in the polymer matrix, and an acetonitrile phase layer onto the polymer matrix. Analyses of the radial distribution functions indicate that the all-anti conformation, the relative disposition of adjacent PEDOT chains and the distribution of ClO4- dopant ions are fully consistent with periodic DFT predictions. The agreement between two such different methodologies allows reinforcing the microscopic understanding of the PEDOT film structure.

Origin of Blue-Green Emission in α-Zn2P2O7 and Local Structure of Ln3+ Ion in α-Zn2P2O7:Ln3+ (Ln = Sm, Eu): Time-Resolved Photoluminescence, EXAFS, and DFT Measurements.

Considering the fact that pyrophosphate-based hosts are in high demand for making highly efficient luminescence materials, we doped two visible lanthanide ions, viz. Sm3+ and Eu3+, in Zn2P2O7. Interestingly, it was oberved that pure Zn2P2O7 displayed blue-green dual emission on irradiation with ultraviolet light. Emission and lifetime spectroscopy shows the presence of defects in pyrophosphate samples which are responsible for such emission. DFT calculations clearly pinpointed that the electronic transitions between defect states located at just below the conduction band minimum (arises due to VO1+ and VO2+ defects) and valence band maximum, as well as impurity states situated in the band gap, can lead to dual emission in the blue-green region, as is also indicated by emission and lifetime spectra. X-ray absorption near edge spectroscopy (XANES) shows the stabilization of europium as well as samarium ion in the +3 oxidation state in α-Zn2P2O7. The fact that α-Zn2P2O7 has two different coordination numbers for zinc ions, i.e. five- and six-coordinate, the study of dopant ion distribution in this particular matrix will be an important step in realizing a highly efficient europium- and samarium-based red-emitting phosphor. Time resolved photoluminescence (TRPL) shows that both of these ions are heterogeneously distributed between five- and six-coordinated Zn2+ sites and it is the six-coordinated Zn2+ site which is the most favorable for lanthanide ion doping. Extended X-ray absorption fine structure (EXAFS) measurements also suggested that a six-coordinated zinc ion is the preferred site occupied by trivalent lanthanide ions, which is in complete agreement with TRPL results. It was observed that there is almost complete transfer of photon energy from Zn2P2O7 to Eu3+, whereas this transfer is inefficient and almost incomplete in case of Sm3+, which is indeed important information for the realization of pyrophosphate-based tunable phosphors.

Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor.

Effective manipulation of magnetic spin within a semiconductor leading to a search for ferromagnets with semiconducting properties has evolved into an important field of dilute magnetic semiconductors (DMS). Although a lot of research is focused on understanding the still controversial origin of magnetism, efforts are also underway to develop new materials with higher magnetic temperatures for spintronics applications. However, so far, efforts toward quantum-dots(QDs)-based DMS materials are plagued with problems of phase separation, leading to nonuniform distribution of dopant ions. In this work, we have developed a strategy to synthesize highly crystalline, single-domain DMS system starting from a small magnetic core and allowing it to diffuse uniformly inside a thick CdS semiconductor matrix and achieve DMS QDs. X-ray absorption fine structure (XAFS) spectroscopy and energy-dispersive X-ray spectroscopy-scanning transmission electron microscopy (STEM-EDX) indicates the homogeneous distribution of magnetic impurities inside the semiconductor QDs leading to superior magnetic property. Further, the versatility of this technique was demonstrated by obtaining ultra large particles (∼60 nm) with uniform doping concentration as well as demonstrating the high quality magnetic response.

Structure modeling of terbium doped strontium-lanthanum borate

Terbium doped strontium-lanthanum borate, Sr3La2(BO3)4:Tb (SLB), was studied by semi-empirical computational approaches using PM6 parametrization and the SPARKLE model for lanthanide(III) (Ln(III)) cations. The focus of interest was on structural aspects, e.g. the cell parameters and distribution of dopant ions between various sites as a function of dopant concentration. The cell linear dimensions were calculated to decrease linearly with increasing dopant molar concentration. SLB offered two sites for the dopant. Calculations predicted that one of these sites should be preferred by the Tb(III) dopant. The optimized cell dimensions as well as the total energies differed for structures with dopant exclusively in site 1 or site 2. Computational predictions were tested against experimental results obtained for SLB synthesized by sol-gel method varying the dopant concentration. The agreement between experimental and computational results was found sufficiently promising to continue the computational studies.

Photoluminescence and EPR studies on Fe³⁺ doped ZnAl₂O₄: an evidence for local site swapping of Fe³⁺ and formation of inverse and normal phase.

Considering that ZnAl2O4 spinel has two different sites (octahedral and tetrahedral) and its properties change with dopant ion distribution among these two sites; ZnAl2O4 doped with varied concentrations of Fe(3+) was synthesized by a low temperature sol-gel combustion method. Phase purity and structural investigations were carried out using Rietveld refined X-ray diffraction which shows a decrease in the value of cell parameters at higher doping levels. Photoluminescence (PL) and electron paramagnetic resonance (EPR) studies have shown that on doping, Fe(3+) ions were distributed in both tetrahedral and octahedral sites. At octahedral sites, Fe(3+) exhibited a broad red emission around 745 nm while at tetrahedral sites it exhibited well-defined vibronic sidebands at 665, 674, 684 and 693 nm along with a broad blue band with a maxima at 445 nm at room temperature. EPR studies have shown a broad spectrum at g ≈ 2.2 which corresponds to the Fe(3+) in octahedral sites, while the broad signal at g ≈ 4.2 belongs to Fe(3+) in tetrahedral sites. It was also inferred from these studies that Fe(3+) prefers to occupy octahedral sites at higher concentrations and at higher annealing temperatures. The PL decay behavior of Fe(3+) in ZnAl2O4 has also shown that two different types of Fe(3+) ions were present in this matrix. The first type was a long lived species (τ ≈ 170 μs) present at octahedral sites and the other was a short lived species (τ ≈ 40 μs) present at the tetrahedral sites; the fraction of the long lived species predominate at higher concentrations. Thus the present work is mainly focused on understanding the tuning of local site occupancy of the dopant ion among those sites with varying concentration and annealing temperature, using the dopant ion itself as a spectroscopic probe, which further helps in understanding the phase (inverse and normal) of the spinel.

Proton transport in doped yttrium oxide. Monte-Carlo simulation

The Monte-Carlo technique is used to calculate the dependences of the tracer diffusion coefficient D* and conductivity σ of protons on the temperature and content x of the acceptor dopant in oxides with the structure of distorted fluorite (“bixbyite” structure). Analysis is carried out for the calcium doped Y2O3 oxide as an example. The effect of dopant-generated traps (different energy states for protons) and also the effect of site blocking due to interaction of protons between themselves and with oxygen vacancies are considered. It is shown that mobility of protons decreases significantly as a result of doping already at low x ∼ 1 mol %. The behavior of conductivity noticeably depends on the distribution of dopant ions over nonequivalent cation sites in the lattice. The predominant dopant distribution over the sites of the same type accounts for the appearance of a maximum in the dependence of σ(x) when correlations are taken into account.

Energy transfer kinetics in oxy-fluoride glass and glass-ceramics doped with rare-earth ions

An investigation of donor-acceptor energy transfer kinetics in dual rare earths doped precursor oxy-fluoride glass and its glass-ceramics containing NaYF4 nano-crystals is reported here, using three different donor-acceptor ion combinations such as Nd-Yb, Yb-Dy, and Nd-Dy. The precipitation of NaYF4 nano-crystals in host glass matrix under controlled post heat treatment of precursor oxy-fluoride glasses has been confirmed from XRD, FESEM, and transmission electron microscope (TEM) analysis. Further, the incorporation of dopant ions inside fluoride nano-crystals has been established through optical absorption and TEM-EDX analysis. The noticed decreasing trend in donor to acceptor energy transfer efficiency from precursor glass to glass-ceramics in all three combinations have been explained based on the structural rearrangements that occurred during the heat treatment process. The reduced coupling phonon energy for the dopant ions due to fluoride environment and its influence on the overall phonon assisted contribution in energy transfer process has been illustrated. Additionally, realization of a correlated distribution of dopant ions causing clustering inside nano-crystals has also been reported.

Electrical and electron paramagnetic resonance spectroscopy characterization of Mn-doped nanostructured TiO2 for capacitor applications

Nanostructured TiO2 has shown promise as a dielectric material for high energy density ceramic capacitors because of its high dielectric breakdown strength and dielectric constant. Strategies to increase the insulation resistance or to reduce the leakage current of TiO2 include doping with transition metal ions. It is shown that Mn doping followed by an appropriate thermal treatment increases the grain boundary resistivity significantly and lowers the dielectric loss. Electrical measurements along with electron paramagnetic resonance and scanning electron microscopy of Mn-doped nanoscopic TiO2 demonstrate that sintering at 900°C leads to optimal electrical properties that are correlated with a non-uniform distribution of dopant ions, concentrated at the grain boundaries. Nanostructured TiO2 dielectrics with improved insulation resistance are promising for the development of higher energy density capacitors.

Nonstatistical Dopant Distribution of Ln3+-Doped NaGdF4 Nanoparticles

Oleate-stabilized NaGdF4 nanoparticles codoped with 20% Y3+ and 5% Tb3+ (NaGdF4:Y,Tb), with 20% Nd3+ (NaGdF4:Nd), and with 20% Tb3+ (NaGdF4:Tb) were prepared in organic medium. The distribution of dopant ions was studied using synchrotron radiation X-ray photoelectron spectroscopy along with X-ray powder diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and luminescence spectroscopy. Results show that these nanoparticles do not have the intended statistical dopant distribution despite the fact that different synthesis procedures and dopant ions with different ionic radii were used. NaGdF4:Y,Tb nanoparticles have a subtle gradient structure with Gd3+ more concentrated toward the center and Y3+ more concentrated toward the surface of the nanoparticles. NaGdF4:Nd nanoparticles have a steep gradient structure with Gd3+ more concentrated toward the center and Nd3+ more concentrated toward the surface of the nanoparticles. Even NaGdF4:Tb nanoparticles have a steep gradient structure with Tb3+ more concentrated toward the center and Gd3+ more concentrated toward the surface of the nanoparticles in spite of the very similar ionic radius of Gd3+ and Tb3+. This work shows that the general assumption that Ln3+ dopant ions in lanthanide-based nanoparticles are statistically distributed in the whole nanoparticle may not be true.

Distribution of Eu ions in Y2O3:Eu nanopowders prepared by solution combustion method

AbstractY2O3:Eu nanopowder was prepared by urea solution combustion method. The samples were then characterized by X‐ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The XRD patterns of samples were investigated by Warren‐Averbach method in order to determine crystallite size and strain distribution. An innovative method was developed for prediction of dopant ion distribution in host lattice using Warren‐Averbach method and micro‐strain distribution. Analyzing of Y2O3:Eu nanopowder by this method revealed that the Eu ions preferentially accumulated in near the grain boundaries more than the inner parts of crystallites. The good match between the crystallite size distribution prediction by Warren‐Averbach method and distribution calculated from HRTEM image was obtained (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Local environment of Eu3+ and Tb3+ ions in fluorophosphate glasses of the Ba(PO3)2-MgCaSrBaAl2F14 system

The induced optical absorption and EPR absorption spectra of fluorophosphate glasses of the compositions 40Ba(PO3)2 · 60MgCaSrBaAl2F14 and 5Ba(PO3)2 · 95MgCaSrBaAl2F14 doped with Tb3+ and Eu3+ ions are investigated within the model of the effective capture volume of free carriers. The concentration dependences of the relative number of radiation centers on the dopant concentration in fluorophosphate glasses are analyzed. It is established that the character of the distribution of dopant ions in glasses depends on the dopant concentration and the structure of the glass. The critical concentrations at which the oxygen local environment of Eu3+ or Tb3+ ions in the structure of fluorophosphate glasses transforms into a mixed local environment are determined for glasses of the compositions under investigation.

Exploring the Room-Temperature Synthesis and Properties of Multifunctional Doped Tungstate Nanorods

Uniform Mn-doped alkaline-earth metal tungstate—AWO4 (A = Ca, Sr, Ba)—nanorods of reproducible size, shape, and composition have been methodically prepared using a modified template-directed methodology under ambient, room-temperature conditions. The dopant ion distribution within the nanostructures does not appear to adversely affect either the structural or crystalline integrity of our as-prepared compounds, as determined by microscopy and diffraction studies. What is much more important is the fact that the presence of Mn2+ not only substantially increases the photoluminescent potential of a pristine tungstate material but also reinforces its versatility by adding a desirable magnetic component to its repertoire of properties. In so doing, we have created multifunctional one-dimensional nanorods with exciting opto-magnetic behavior, which should become important for the future incorporation of these materials into functional nanoscale devices, with various potential applications in a number of diverse fields.

Oxide ion diffusion in perovskite-structured Ba 1− xSr xCo 1− yFe yO 2.5: A molecular dynamics study

Molecular dynamics simulations are used to examine the relationship between oxide ion conductivity and dopant content in systems of general formula Ba 1− x Sr x Co 1− y Fe y O 2.5, where x and y are varied between 0 and 1, and all B-site cations are assumed to be in the + 3 state. Doping Ba-rich systems with iron initially causes a decrease in the ionic conductivity, which reaches a minimum around 50 at.% Fe. Above this concentration, the conductivity increases again to a maximum for y = 1. For Sr-rich systems ( x = 1.0), the conductivity increases continuously as y is increased. Simulations using a mean field approximation for the short-range Co 3+/Fe 3+ interactions are also reported; comparison with the discrete ion model results shows that the parabolic variation in the ionic conductivity is due to a mixing effect caused by the random distribution of dopant ions in the perovskite structure. Calculation of coordination numbers for each cationic species shows that anion vacancies tend to be strongly associated with Co 3+ ions, and that the strongest bonding occurs when y = 0.5. Doping with Sr 2+ was found to increase the conductivity. These results show that compositional changes have a strong effect on the oxide ion conductivity when the concentration of oxygen vacancies is held constant.

A model of the capture volume of free carriers in fluorophosphate glasses doped with terbium

The induced electron paramagnetic resonance (EPR) and optical absorption spectra of Tb2O3-doped glasses in the LiF-MgF2-Ba(PO3)2 system are investigated. The intensities of the doublet signals from PO 4 2− and PO 3 2− centers in regions with different contents of the fluoride component are determined as functions of the terbium concentration. It is shown that fluorophosphate glasses can be characterized by two values of the capture volume parameter, which differ by a factor of 5.0–6.6 depending on the dopant concentration. In the range of minimum dopant concentrations at which the capture volume is maximum, the dopant ions have a hypothetically phosphate environment. It is suggested that the capture volume parameter defined by the expression lnc/c 0 = −VC 3 can be treated as a characteristic of the distribution of dopant ions in fluorophosphate glasses.

Effect of doping on the density-of-states distribution and carrier hopping in disordered organic semiconductors

The effect of doping on the density-of-states (DOS) distribution and charge-carrier transport in a disordered hopping system is considered analytically. It is shown that doping such a system produces a random distribution of dopant ions, which Coulombically interact with carriers localized in intrinsic hopping sites. This interaction further increases the energy disorder and broadens the deep tail of the DOS distribution. Therefore, doping of a disordered organic semiconductor, on the one hand, increases the concentration of charge carriers and lifts up the Fermi level but, on the other hand, creates additional deep Coulombic traps of the opposite polarity. While the former effect facilitates conductivity, the latter strongly suppresses the carrier hopping rate. A model of hopping in a doped disordered organic semiconductor is suggested. It is shown that the doping efficiency strongly depends upon the energy disorder and external electric field.