Er Doping Level Research Articles

The Role of Er3+ Content in the Luminescence Properties of Y3Al5O12 Single Crystals: Incorporation into the Lattice and Defect State Creation

Erbium-doped Y3Al5O12 (YAG) single crystals grown using the micro-pulling-down technique were investigated. Three Er concentrations were chosen: 0.1, 0.3 and 1 at%. Er3+ electron paramagnetic resonance (EPR) spectra were measured in the ground and first excited states. The corresponding g tensors and 167Er hyperfine interaction were changing upon Er content indicating moderation of the Er-O bond length and/or Er local surrounding. Photoluminescence (PL) and radioluminescence (RL) spectra were complex, consisting of strongly overlapped typical Er3+ transitions. In addition, there were other broad PL band (3.1 eV) and RL band (3.95 eV) attributed to the F+ center and yttrium substituting for aluminum (YAl), respectively. The X-ray excited decay kinetics exhibited a decrease of the decay time of the YAl from hundreds of nanoseconds to nanoseconds upon Er doping level. This is discussed and explained considering EPR data.

Determination of optimum Er-doping level to get high transparent and low resistive Cd1 − xErxS thin films

Cd1 − xErxS (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10) thin films were produced by a chemical route on glass slides. The structural, morphological, optical and electrical properties of the grown samples were studied to obtain the optimum Er-doping level. Structural properties indicated that specimens had a hexagonal structure. Morphological analysis showed that the grain size of pristine CdS thin films remarkably reduced with rising Er-doping. The presence of Er atoms in CdS host structure was proved by energy dispersive of X-ray spectroscopy (EDS). The transparency of CdS thin films substantially improved after 10 at.% Er-doping and a gradual decrease was acquired in the band gaps of the CdS samples with the increase of Er-doping. Photoluminescence data approved the existence of two main peaks corresponding to the green and yellow regions. Electrical properties of pristine CdS thin films were enhanced by Er-doping and the best electrical conclusions were obtained for Cd0.94Er0.06S thin films. Thus, it can be brought to an end that Er-doping enhanced both optical and electrical properties of pristine CdS thin films, which are of vital importance in optoelectronic applications.

Synthesis and Characterization of Er-Doped Nano ZnO Samples

Pure and erbium-doped ZnO nanoparticles (Zn1−xErxO), (0.00 ≤ x ≤ 0.10), were synthesized by wet chemical co-precipitation method. The structural, optical, and magnetic properties of the prepared samples were investigated using x-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), M-H magnetic hysteresis, and electron paramagnetic resonance (EPR). XRD studies exhibit the presence of a single ZnO wurtzite hexagonal crystal structure for 0.00 ≤ x ≤ 0.06. A secondary phase of Er2O3 appears for x > 0.06. This means that the solubility limit for doping Zn2+ ions by Er3+ ions is about x = 0.06 under our preparations condition. The lattice parameter a is not affected by the Erbium doping. On the other hand, the lattice parameter c and the unit cell volume V increase with the increase of x up to x = 0.06. This is attributed to the larger ionic size of Er3+ ions (0.88 A) compared to Zn2+ ions (0.74 A). Both c and V decrease for x > 0.06. TEM micrographs indicate that the shape and the size of the ZnO nanoparticles are modified by changing the doping level of Er. The UV measurements point out that band gap energy Eg decreases with the increase of x up to x = 0.06. Then, it increases for both x = 0.08 and 0.10. FTIR spectra confirm the presence of O–H and Zn–O stretching modes at 3451.963 and 428.901 cm− 1, respectively, in pure and doped ZnO samples. The Zn–O stretching mode shifts toward a lower wavenumber for x = 0.06 and toward a higher wavenumber for x = 0.10. M-H hysteresis analysis, at room temperature, reveals that the pure ZnO has a ferromagnetic signal combined with diamagnetic and paramagnetic contributions. This ferromagnetism is reduced for the doped samples up to x = 0.02, and an antiferromagnetic alignment appears for 0.04 ≤ x ≤ 0.10. The saturation magnetization (Ms), the coercivity (Hc), the retentivity (Mr), the anisotropy constant (Ka), and the magnetic moment (μm) were estimated and discussed in terms of erbium doping for the different samples. EPR spectra for Zn1−xErxO were measured at room temperature in order to study the effect of Er substitution on the g value, resonance field (Hr), peak to peak line width (ΔHpp) and spin–spin relaxation time constant (T2).

On the potential of Er-doped AlN film as luminescence sensing layer for multilayer Al/AlN coating health monitoring

Luminescence sensing is an attractive approach for in-situ monitoring the health and integrity of multilayered surface protective coatings on highly active metals. In this work, we demonstrate the potential of erbium (Er) doped aluminum nitride (AlN) films to be applied as luminescence sensing layer in the Al/AlN multilayered coating system. The AlN:Er films were prepared by radio-frequency magnetron sputtering from Al targets doped with varied concentrations (from 0.5 at.% to 2.5 at.%) of Er. The chemical composition, surface morphology, crystal structure, chemical state and optical properties of the deposited AlN:Er films were investigated. We found that the crystal structure, surface roughness and optical properties of the AlN:Er films have strong correlations with the Er doping level. The as-deposited AlN:Er films showed the characteristic photoluminescence emission lines of the trivalent Er ions in the visible frequency range and quenching was observed when the Er doping level increased to 2.5 at.%. This work signifies the viability of AlN:Er film as luminescence sensing layer and the optimal Er doping concentration of the Al sputtering target is 2.0 at.% for practical applications.

Toward the realization of erbium-doped GaN bulk crystals as a gain medium for high energy lasers

Er-doped GaN (Er:GaN) is a promising candidate as a gain medium for solid-state high energy lasers (HELs) at the technologically important and eye-safe 1.54 μm wavelength window, as GaN has superior thermal properties over traditional laser gain materials such as Nd:YAG. However, the attainment of wafer-scale Er:GaN bulk or quasi-bulk crystals is a prerequisite to realize the full potential of Er:GaN as a gain medium for HELs. We report the realization of freestanding Er:GaN wafers of 2-in. in diameter with a thickness on the millimeter scale. These freestanding wafers were obtained via growth by hydride vapor phase epitaxy in conjunction with a laser-lift-off process. An Er doping level of 1.4 × 1020 atoms/cm3 has been confirmed by secondary ion mass spectrometry measurements. The freestanding Er:GaN wafers exhibit strong photoluminescent emission at 1.54 μm with its emission intensity increasing dramatically with wafer thickness under 980 nm resonant excitation. A low thermal quenching of 10% was measured for the 1.54 μm emission intensity between 10 K and 300 K. This work represents a significant step in providing a practical approach for producing Er:GaN materials with sufficient thicknesses and dimensions to enable the design of gain media in various geometries, allowing for the production of HELs with improved lasing efficiency, atmosphere transmission, and eye-safety.

Red shifts of the Eg(1) Raman mode of nanocrystalline TiO2:Er monoliths grown by sol–gel process

Nanocrystalline monoliths of Er doped TiO2 were prepared by the sol–gel technique, by controlling the Er-doping levels into the TiO2 precursor solution. As-prepared and annealed in air samples showed the anatase TiO2 phase. The average diameter of the nanoparticles ranged from 19 to 2.6nm as the nominal concentration of Er varies from 0% to 7%, as revealed by EDS analysis in an electron microscope. Photo Acoustic Spectroscopy (PAS) allowed calculate the forbidden band gap, evidencing an absorption edge at around 300nm, attributed to TiO2 and evidence of electronic transitions or Er3+. The Raman spectra, corresponding to the anatase phase, show the main phonon mode Eg(1) band position at 144cm−1 with a red shift for the annealing samples.

Intensive up-conversion photoluminescence of Er3+-doped Bi7Ti4NbO21 ferroelectric ceramics and its temperature sensing

The intensive up-conversion (UC) photoluminescence and temperature sensing behavior of Er 3+-doped Bi 7 Ti 4 NbO 21( BTN ) ferroelectric ceramics prepared by a conventional solid-state reaction technique have been investigated. The X-ray diffraction and field emission scanning electron microscope analyses demonstrated that the Er 3+-doped BTN ceramics are single phase and uniform flake-like structure. With the Er 3+ ions doping, the intensive UC emission was observed without obviously changing the properties of ferroelectric. The optimal emission intensity was obtained when Er doping level was 15 mol.%. The temperature sensing behavior was studied by fluorescence intensity ratio (FIR) technique of two green UC emission bands, and the experimental data fitted very well with the function of temperature in a range of 133–573 K. It suggested that the Er 3+-doped BTN ferroelectric ceramics are very good candidates for applications such as optical thermometry, electro-optical devices and bio-imaging ceramics.

The Verdet constant of Er-doped crystalline YAG and tellurite glass at 1645 nm

We describe the measurement of the Verdet constant of undoped and Er-doped crystalline YAG and tellurite glass at 1645 nm. The undoped YAG value is compared to those measured using visible light. We show that the paramagnetic nature of Er reduces the Verdet constant but that the decrease is probably not significant for the typical Er doping levels used in Er:YAG or in Er:tellurite-glass mid-IR lasers.

Magnetic tri-axial orientation in (Y1−xErx)2Ba4Cu7O15−y superconductors

We report the tri-axial grain-orientation effects under a modulated rotation magnetic field for (Y1−xErx)2Ba4Cu7Oy [(Y,Er)247]. The magnetic easy axis at room temperature was drastically changed around x∼0.1; however, the Er-doping levels for the conversion of magnetic easy axes from the c-axis to the ab-direction and from the a- to b-axes were quite different. Tri-axial single-ion magnetic anisotropy of Er3+ was roughly 10 times greater than tri-axial magnetic anisotropy generated by both the superconducting CuO2 plane and the blocking Cu–O chain layer. An appropriate choice of rare-earth (RE) ions in RE-based cuprate superconductors enables the reduction of the required magnetic field for the production of bulks and thick films based on the magnetic orientation technique.

Features in the photoluminescence line-shape of heavily Er-doped Ge–S–Ga glasses

Erbium doped chalcogenide glasses are of great interest in the integrated optoelectronic technology due to their Er 3+ intra-4f emission at the standard telecommunication wavelength of 1.54 μm. In this paper, the photoluminescence (PL) of a series of (GeS 2) x (Ga 2S 3) 100− x ( x = 75 and 67) glasses doped with high amounts of Er 2S 3 (1.8, 2.1, 2.4 and 2.7 mol%) under excitation with 1064 nm light has been studied. A quenching PL effect at 1.22 аt.% Er-doped (GeS 2) 75(Ga 2S 3) 25 and 1.39 аt.% Er-doped (GeS 2) 67(Ga 2S 3) 33 glasses has been established. The relative changes in PL line-shape at around 1540 nm have been estimated by deconvoluting the spectra to Gaussian sub-bands centered at 1519 ± 1, 1537 ± 1, 1546 ± 1, 1555 ± 1 and 1566 ± 4 nm, which correspond to F 21, F 11, F 22, F 12 and F 13 transitions in the 4 I 13 / 2 and 4 I 15 / 2 energy levels and have intensity and manifestation that are strongly depend on the Er-doping level. The influence of gallium on the PL efficiency has been evaluated with a view to enhanced emission cross-section.

Growth and characterization of Er-doped single crystal lithium niobate fibers

Single crystal lithium niobate fibers with diameters ranging from 1to3mm have successfully been grown by the micro-pulling-down technique. The fibers are doped with various Er doping levels from 0to0.7mol% and appear to be transparent and crack-free. The study includes x-ray structural investigation and complete spectroscopic characterization. The analysis shows a good homogeneity of composition, and the comparison with bulk crystals demonstrates the good optical quality of the samples. Particular attention has been devoted to the measurements of the fluorescence decay time of the I13∕24 Er level, which has been carried out with a particular technique in order to avoid radiation trapping effects. Results are in agreement with the literature both in the case of bulk crystals and of fibers. Reliable polarized emission cross section in the 1.5μm region are presented.

Electrical properties of Er-doped CdS thin films

Cadmium sulfide thin films were prepared by chemical bath on glass substrates at 80°C. CdS was Er-doped during the growth process by adding water-diluted Er(NO3)33∙H2O to the CdS aqueous growing solution. The relative volume of the doping solution was varied in order to obtain different doping levels. The crystalline structure of CdS:Er films was cubic zinc blende for all the doped layers prepared. The (111) interplanar distance has an irregular variation with the Er doping level. Consequently, the band gap energy (Eg) firstly increases and afterward diminishes becoming, at last, approximately constant at around Eg=2.37eV. For higher doping levels, in the as-grown films, dark electrical conductivity (σ) values reach 1.8×10−2Ω−1cm−1 at room temperature. The logarithm of σ vs 1∕kT plot, where k is Boltzmann’s constant and T the absolute temperature, indicates an effective doping of CdS as a result of the Er introduction into the lattice of the material. Hall effect measurements reveal a n-type doping with 2.8×1019cm−3 as maximum carrier density.

Er coordination in Y2O3 thin films studied by extended x-ray absorption fine structure

Extended x-ray absorption fine structure (EXAFS) spectroscopy was employed to study the Er coordination in polycrystalline Y2O3 thin films, which was found to dictate their photoluminescence (PL) properties. Incorporation of Er with concentrations varying from 6to14at.% was achieved by radical-enhanced atomic layer deposition at 350°C. In all samples, Er was found to be in the optically active trivalent state, confirmed by their x-ray absorption near-edge spectroscopy spectra. Modeling of the EXAFS data revealed that the local structure of Er3+ is similar to that of Er3+ in Er2O3. Specifically, Er3+ is coordinated with six O at 2.24 and 2.32Å. Excellent fits to the EXAFS for samples with Er3+ concentration less than 8at.% were achieved when the second coordination shell was modeled as a mixture of Y3+ and Er3+, indicating a complete miscibility of Er3+ in the Y2O3 matrix under these experimental conditions. This behavior is attributed to the almost perfect ionic size match between Y3+ and Er3+, having identical valence state and coordination characteristics. For thin films with higher Er concentrations, the EXAFS analysis revealed an exsolution with Er2O3 domain. Since there is no indication of Er clustering, it is concluded that the PL quenching observed in samples with the Er doping level exceeding 8at.% is likely due to Er ion-ion interaction but not Er immiscibility in Y2O3. Specifically, an increase in the Er3+ concentration implied an increase in the average number of Er3+ in the second coordination shell, thus making ion-ion interaction possible. The critical interionic distance between two Er3+ was determined to be ∼4Å, thus setting an upper limit on the Er3+ concentration in Y2O3 at ∼6×1021cm−3, at least three orders of magnitude higher than the Er3+ solubility limit in the conventional SiO2 host (<1018cm−3).

1.54 µm Er3+ electroluminescence from an erbium-compound-doped organic light emitting diode with a p-type silicon anode

By doping an erbium complex, erbium (III) 2, 4-pentanedionate (Er(acac)3), into the ALQ layer, we fabricate a series of infrared emission organic light emitting diodes (OLED) with structures of p-Si/SiO2/NPB/ALQ/ ALQ:Er(acac)3/ALQ/Sm/Au, where p-Si is the anode and Sm/Au is the cathode. The 1.54 µm emission from Er3+ is observed. The impact of doping level of Er(acac)3 in ALQ on 1.54 µm electroluminescence (EL) intensity is studied, and the best mass ratio of Er(acac)3 to ALQ is found at 1 : 60. A competitive EL mechanism from the ALQ and Er(acac)3 is found and the Er3+ ions excitations are attributed to energy transfer from the ligands to Er ions.

Light-induced absorption in reduced congruent and near-stoichiometric Er:LiNbO3 crystals

Light-induced absorption (LIA) in thermally reduced congruent and near-stoichiometric Er:LiNbO3 crystals, which have different cuts of crystal (X- and Y-cut) and different doping levels of Er3+ (0.2, 0.4, 0.6 and 1.0 mol %), has been studied within continuous-wave light intensity by using polarized 632.8 nm beam as probe light and polarized 488 nm beam as pump light. Effects of thermal reduction condition, pump intensity, Li/Nb ratio and Er-doping level on the LIA are summarized and discussed. Studies on spectral characteristics of both linear absorption and light-induced absorption show that photo-ionization of bipolarons into small polarons plays a predominant role in the LIA process. The role of the Er3+ ion in the LIA is investigated by studying the doping level and the thermal reduction effects on the absorption and emission properties of Er3+. The results show the possibility that the Er3+ ion directly participates in the light-induced charge transport is small. It affects the LIA only via the bypassing part of pump intensity to excite near-infrared emissions of Er3+. The thermaleffect on the LIA is demonstrated. A two-center model with inclusion of the thermal contribution can qualitatively explain two major LIA characteristics that include the appearance of a slow stage in the LIA procedure and the unsaturation behavior of the LIA coefficient in high pump intensity regime. In addition, the pump depletion effect on the LIA characteristics is discussed. The possibility of pump beam fanning arising from light-induced scattering is ruled out experimentally.

PHOTOLUMINESCENCE PROPERTIES OF Er DOPED INTO C-RICH SiC NANOPARTICLE FILMS

Polycrystalline silicon carbide ( P-SiC ) films containing SiC nanoparticles and Er were prepared by r.f. reactive magnetron co-sputtering technique with SiC and Er targets on low-temperature silicon (111) and silicon dioxide substrates with the mixed gas of pure argon, methane, and hydrogen. Surface morphology and photoluminescence (PL) properties of them were measured by field-emission scanning electron microscope and Raman spectroscopy. The peak position, intensity, and the full width at half maximum (FWHM) of PL spectra were relevant with Er doping levels and deposition conditions.

Blanket neutronics of Li/vanadium-alloy and Flibe/vanadium-alloy systems for FFHR

Neutronics calculations were carried out to characterize self-cooled Li and Flibe blankets with vanadium alloy (V–4Cr–4Ti) structure, as advanced options for the Force Free Helical Reactor (FFHR-2). In the present paper, the parameter dependence of Tritium Breeding Ratio (TBR) and neutron shield performance was examined for a Li blanket (FFHR-LV) and a Flibe blanket (FFHR-FV). The TBR was independent from the Flibe composition between 30 and 45 mol% of BeF 2 in the case of the FFHR-FV. Due to the increase in the temperature range of the coolant Flibe as a result of the change of the structural materials from JLF-1 (low activation ferritic steel) to V–4Cr–4Ti, the fraction of BeF 2 can be changed from 43 to 31 mol% without changing the margin to coagulation of Flibe. The compositional change of Flibe resulted in a significant decrease in its viscosity. The decrease of TBR by the effects of MHD insulator coating with Er was negligibly small with the expected doping level of Er in the FFHR-LV. The increase in the B 4C in the shielding material resulted in the decrease in the fast neutron flux at the superconducting magnet by 60–70% in both FFHR-LV and FFHR-FV. Optimum neutronics performance for the two blanket systems was derived by the calculation.

Raman scattering study of reduced Er:LiNbO3 crystals

Raman spectra of as-grown and reduced (or annealed) Er:LiNbO3 crystals, which have different cut orientations, varied Li/Nb ratio, and different Er-doping levels of 0.2, 0.4, 0.6, 1.0, and 2.0 mol%, were recorded at room temperature over a wavenumber range of 50–1000 cm-1 by use of backward scattering geometries. The spectra are assigned on the basis of their Raman scattering features and previous relevant work. A weak but well-resolved peak around 633 cm-1 appears in the E(TO) spectra that were recorded under the configuration of X(ZY)X(for an X-cut sample) or Y(ZX)Ȳ(for a Y-cut sample) for all crystals studied. The appearance of this peak in the E(TO) spectrum provides further evidence for a previous attribution of this peak to E(TO9) mode. Some additional peaks distributed in the low wavenumber region ranging from 101–137 cm-1 are attributed to Er3+ fluorescence with a wavelength range of 490.41–491.3 nm. The reduction effects include a significant drop of the Raman scattering intensity and a slight narrowing instead of a broadening in the linewidth. The reduction procedure hardly affects the spectral shape and the wavenumber of most of the phonons. The anneal effect is similar to the reduction effect and both effects are not as obvious as the vapor transport equilibration (VTE) effect. In addition, the present Raman scattering result provides evidence for our earlier reported individual result on light-induced diffraction from strongly reduced Er:LiNbO3 crystals.

Emission characteristics of vapor transport equilibrated Er:LiNbO3 crystals

At room temperature, polarized visible and near infrared emission characteristics of 488 nm pumped vapor transport equilibration (VTE) treated Er:LiNbO3 crystals were investigated in comparison with the corresponding as-grown ones. The observed characteristics of the VTE crystal, whether it precipitates or not, include the retained polarization dependence, slight shift (less than 5 Å) of peak position, narrowing of some individual emission peaks, the appearance of additional emission peak near 1536.5 nm and the about 10% lengthening of 1.5 μm lifetime. In addition, in the case of lower Er doping level, the spectral shape are well reserved for the VTE crystals and no obvious changes in both visible and IR emission intensity. On the other hand, for those highly doped crystals, the VTE treatment not only results in a definite change of relative intensity between some emission peaks in IR region, but also causes the drop of both visible and IR emission intensity. Combining with the related absorption characteristic allow to conclude that the drop of the emission intensity results from the scattering of the nanocrystalline grains inside these crystals formed by VTE treatment.

Influence of vapor transport equilibration on Raman spectra of Er:LiNbO 3 crystals

Raman spectra of as-grown and vapor transport equilibration (VTE) treated Er:LiNbO 3 crystals, which have different cut orientations ( X-cut and Z-cut), different Er-doping levels (Er:(0.2, 0.4 and 2.0 mol%)LiNbO 3) and different VTE durations (80, 120, 150 and 180 h), were recorded at room temperature in the wavenumber range 50–1000 cm −1 by using backward scattering geometry. The spectra were attributed on the basis of their spectral features and the previous experimental work and the most recent theoretical progress in lattice dynamics on pure LiNbO 3. In comparison with the pure crystal the most remarkable effect of Er-doping on the Raman spectrum is observed for the E(TO 9) mode. It does not appear at 610 cm −1 as the pure crystal, but locates at 633 cm −1. In addition, the doping also results in the lowering of the Raman phonon frequency, the broadening of the Raman linewidth and the changes of the relative Raman intensity of some peaks. The VTE treatment results in the narrowing of the linewidth, the recovery of the lowered phonon frequency and the further changes of relative Raman intensity. The narrowing of Raman linewidth indicates that the VTE processing has brought these crystals closer to stoichiometric composition. The VTE treatment has induced the formation of a precipitate ErNbO 4 in the high-doped Er(2.0%):LiNbO 3 crystals whether X- or Z-cut. For these precipitated crystals, besides above linewidth and phonon frequency features, they also display more significant Raman intensity changes compared with those not precipitated crystals. In addition, a slight mixing between A 1(TO) and E(TO) spectra is also observed for these precipitated crystals. Above doping and VTE effects on Raman spectra were quantitatively or qualitatively correlated with the characteristics of the crystal structure and phonon vibrational system.