Low Doped Samples Research Articles

Doping dependent intrinsic magnetization in silicon in Ni/Si heterostructures

This investigation delves into the complex interaction at metal-semiconductor interfaces, highlighting the magnetic proximity effect in Ni/Si interfaces through systematic X-ray magnetic circular dichroism (XMCD) studies at Ni and Si edges. We analyzed two Ni/Si heterostructures with differing semiconductor doping, uncovering a magnetic proximity effect manifesting as equilibrium magnetization in the semiconductor substrate induced by the adjacent Ni layer. Our results display distinct magnetization signs corresponding to the doping levels: low-doped samples show parallel alignment to the Ni layer, while high-doped samples align antiparallel, indicating a nuanced interplay of underlying magnetization mechanisms. These findings pinpoint the roles of electron tunneling and exchange splitting modification in the magnetization behavior. The study enriches the understanding of ferromagnetic-semiconductor interface behavior, setting a precedent for the design of advanced spintronic devices that leverage the nuanced magnetic properties of these hybrid systems.

Performance of Fluxgate Magnetometer with Cu-Doped CoFeSiB Amorphous Microwire Core.

In this study, we investigated the effects of Cu doping on the performance of CoFeSiB amorphous microwires as the core of a fluxgate magnetometer. The noise performance of fluxgate sensors primarily depends on the crystal structure of constituent materials. CoFeSiB amorphous microwires with varying Cu doping ratios were prepared using melt-extraction technology. The microstructure of microwire configurations was observed using transmission electron microscopy, and the growth of nanocrystalline was examined. Additionally, the magnetic performance of the microwire and the noise of the magnetic fluxgate sensors were tested to establish the relationship between Cu-doped CoFeSiB amorphous wires and sensor noise performance. The results indicated that Cu doping triggers a positive mixing enthalpy and the reduced difference in the atomic radius that enhances the degree of nanocrystalline formation within the system; differential scanning calorimetry analysis indicates that this is due to Cu doping reducing the glass formation capacity of the system. In addition, Cu doping affects the soft magnetic properties of amorphous microwires, with 1% low-doping samples exhibiting better soft magnetic properties. This phenomenon is likely the result of the interaction between nanocrystalline organization and magnetic domains. Furthermore, a Cu doping ratio of 1% yields the best noise performance, aligning with the trend observed in the material's magnetic properties. Therefore, to reduce the noise of the CoFeSiB amorphous wire sensor, the primary goal should be to reduce microscopic defects in amorphous alloys and enhance soft magnetic properties. Cu doping is a superior preparation method which facilitates control over preparation conditions, ensuring the formation of stable amorphous wires with consistent performance.

Effect of Zn2+ substitution on magnetic properties of the quasi-one-dimensional spin chain compound Ca3CoMnO6

The subtle variation of magnetic structure has large influence on the macroscopic magnetism of Ca3CoMnO6. As the isovalent nonmagnetic ions have no exchange interaction with the adjacent Co2+/Mn4+ and it could keep the valence states and spin states of the Co/Mn ions unchangeably. Introduction of isovalent nonmagnetic ions thus becomes an ideal selection for us to understand the relevant micromechanism. In this paper, a series of Zn2+ substituted Ca3Co1-xZnxMnO6 (0 ≤ x ≤ 0.2) samples were prepared, and the microstructure and magnetic properties were investigated in detail. The XRD results indicate that for low doped samples the larger radius of Zn2+ causes the lattice parameters and volume increase. While for high doped samples the Zn2+ ions enter the octahedral position, resulting in shrinkage of the lattice. The introduction of Zn2+ ions could also influence the magnetic structure of Ca3CoMnO6 effectively. A small amount of nonmagnetic Zn2+ ions well decrease the concentration of the intrinsic defects and help to form more short-range magnetic order. But as the Zn2+ doping concentration increases, the main effect of Zn2+ doping is to release the magnetic frustration of Ca3CoMnO6, and finally a more robust long range antiferromagnetic structure can be established in high doped samples. Simultaneously, the subtle variation of magnetic structure with Zn2+ substitution leads the Ca3Co1-xZnxMnO6 samples present different dynamic behaviors. This interesting finding could serve as a new reference for tuning the magnetic ordering of Ca3CoMnO6 and improving its multiferroic properties.

Defect states and their electric field-enhanced electron thermal emission in heavily Zr-doped β -Ga2O3 crystals

Performing deep level transient spectroscopy (DLTS) on Schottky diodes, we investigated defect levels below the conduction band minima (Ec) in Czochralski-grown unintentionally doped (UID) and vertical gradient freeze-grown Zr-doped β-Ga2O3 crystals. In UID crystals with an electron concentration of 1017 cm−3, we observe levels at 0.18 eV and 0.46 eV in addition to the previously reported 0.86 (E2) and 1.03 eV (E3) levels. For 1018 cm−3 Zr-doped Ga2O3, signatures at 0.30 eV (E15) and 0.71 eV (E16) are present. For the highest Zr doping of 5 × 1018 cm−3, we observe only one signature at 0.59 eV. Electric field-enhanced emission rates are demonstrated via increasing the reverse bias during measurement. The 0.86 eV signature in the UID sample displays phonon-assisted tunneling enhanced thermal emission and is consistent with the widely reported E2 (FeGa) defect. The 0.71 eV (E16) signature in the lower-Zr-doped crystal also exhibits phonon-assisted tunneling emission enhancement. Taking into account that the high doping in the Zr-doped diodes also increases the electric field, we propose that the 0.59 eV signature in the highest Zr-doped sample likely corresponds to the 0.71 eV signature in lower-doped samples. Our analysis highlights the importance of testing for and reporting on field-enhanced emission, especially the electric field present during DLTS and other characterization experiments on β-Ga2O3 along with the standard emission energy, cross section, and lambda-corrected trap density. This is important because of the intended use of β-Ga2O3 in high-field devices and the many orders of magnitude of possible doping.

Metal-doped bioceramic nanopowders with tunable structural properties aimed at enhancing bone density: Rapid synthesis and modeling

Metal doped bioceramic nanopowders were prepared by solid-state mechanochemical reactions. Also, genetic programming (GP) and gene expression programming (GEP) models were developed to predict the structural features of the mechanosynthesized nanopowders aimed at developing an innovative solution to enhance bone mineral density. The substitution of Ca2+ with different ions in the apatite structure was confirmed from chemical analysis and structural assessment, where irregular changes in the lattice parameters and unit cell volume were observed due to the replacement of the Ca2+ bivalent cation with monovalent, bivalent or trivalent ions as well as the carbonate ions effects on the apatite lattice. It was found that the crystallite size and micro-strain of the substituted bioceramics were between ~11 and 98 nm and ~0.31–2.49%, respectively. From the functional group analysis, the intensity of the hydroxyl groups decreased as the dopant content increased. The electron microscopy images showed that both undoped and low-doped samples consist of spheroidal particles in the nano regime, whereas the high-doped specimens exhibited a high propensity to agglomerate. The results of cytotoxicity assays corroborated that appropriate ionic substitution can prevent the toxic effects of Li on Mus musculus fibroblast cells, and thus by increasing dopant concentration up to z = 0.25, cell viability of around 90% was observed. The results obtained from the modeling demonstrated that both GP and GEP methods are reliable in predicting the structural properties of the synthetic metal-doped bioceramic nanopowders.

Effect of Mn doping on the microstructure and magnetic properties of CuFeO2 ceramics

The effects of Mn doping on the microstructure and magnetic properties of CuFeO2 systems were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), and a physical property measurement method. The microstructure measurements demonstrated that the substitution of Mn for Fe can cause lattice distortion, promote grain growth, and change the valence state of Fe and Mn ions. Ceramic samples with doping content x = 0.00−0.03 exhibited two successive magnetic transition temperature (TN) at TN1 ≈ 14 K and TN2 ≈ 10 K. TN decreased gradually with the Mn4+ content, and TN2 was not observed in the x > 0.05 samples within a temperature range of T = 5−300 K. Magnetic hysteresis loops revealed that only anti-ferromagnetic behavior occurred in the low-doped samples (x = 0.00−0.03), and the coexistence of ferromagnetism and anti-ferromagnetism was observed in the high-doped samples (x = 0.05−0.10). Besides, the x = 0.10 sample had a maximum magnetization of 5.98 emu/g. This study provides basic experimental data for investigating the relationship between the microstructure and magnetic properties of CuFeO2 systems.

Mn incorporated MoS2 nanoflowers: A high performance electrode material for symmetric supercapacitor

Energy storage devices based on the two-dimensional transition metal dichalcogenides (TMDs) have great interest due to their fascinating physical and chemical properties. In this study, Mn incorporated MoS2 nanosheets are self-assembled into nanoflowers via a simple one-step hydrothermal process. The nanoflowers retain the feature of the high specific surface area of the nanosheets and the intercalation of Mn atoms up to a certain amount increases the porosity of MoS2, thus enhancing active sites for reaction. The presence of an intermediate oxidation state of Mn (Mn3+), which also plays an important role in increasing capacitance, is highest in low doped sample resulting in superior capacitance performance compared to bare and high Mn content samples. So the supercapacitor electrode made of low Mn incorporated MoS2 nanoflowers exhibits maximum specific capacitance (430 F g−1), energy density 48.9 W h kg−1 and power density 5.0 kW kg−1 with excellent capacitance retention up to 5000 cycles at 10 A g−1, when used as a supercapacitor electrode. Further, the performance of the electrode material has been examined by lightning four LED bulbs in series showing longer discharge time. Our findings open new areas to explore Mn doping with TMDs as next-generation energy devices systematically.

Structural, magnetic and magnetocaloric properties of double perovskites Ba2-xLaxFeMoO6

We report the possible variations in the structural and magnetocaloric properties induced by the controlled La-substitution at the Ba-site in Ba2-xLaxFeMoO6 (0.0 ≤ x ≤ 0.4) samples. The samples were prepared using the conventional solid state reaction method. The X-ray diffraction patterns confirmed the formation of cubic crystal structure (Fm-3m) in all the samples. The magnetization vs. temperature curves showed a single transition from ferromagnetic to paramagnetic phase with increasing temperature. In the low doped samples (up to x = 0.2) the increase in the Curie temperature is attributed to the electronic effects whereas the almost similar TC values recorded in the higher La-doped samples (x = 0.3 and 0.4) is due to the competition between the band filling effect and the steric effect. The Arrott plots confirmed a second order of magnetic phase transition in each sample. The pure Ba2FeMoO6 sample showed the highest magnetic entropy change value of 0.93 Jkg−1K−1 at a low applied field of 2.5 T, the largest relative cooling power (72 Jkg-1) however is observed for the Ba1.9La0.1FeMoO6 sample which is attributed to the broad magnetic entropy curve obtained for this composition. The results obtained here clearly reveal that the Curie temperature and magnetocaloric properties of the host Ba2FeMoO6 material can be effectively modified by La-doping that makes this compound a promising base material for establishing novel magnetic refrigerants.

Exploring determinants of lattice structure and high energy storage properties of Fe-doped SBN ceramics

(Sr0.5Ba0.5)1+xNb2-xFexO6 (SBNF-x, 0 ≤ x ≤ 0.20) ceramics were prepared using the conventional solid-state reaction method. With the increase in x, the tungsten bonze structure of the ceramics will transform from “unfilled” to “filled.” The crystallographic parameters obtained using the Rietveld method on XRD patterns were used to explore the determinants of the lattice structure. Lattice parameter a is dominated by the distance of the A1- and A2-sites via the Coulomb interaction. The average bond length of Nb1O4 controls the change of c due to the symmetrical environment around the Nb1O6 octahedron. High energy storage properties appear in low doping samples. The discharge energy density of SBNF-0.02 is 0.595 J/cm3, with a storage efficiency of 91.3%, and of SBNF-0.04 is 0.680 J/cm3, 5.3 times the value of SBNF-0, with a storage efficiency of 83.6%. SBNF-x (0.02 ≤ x ≤ 0.04) ceramics with high discharge energy density and high storage efficiency are promising candidates for producing high energy density capacitors.

Enhanced dielectric properties in la modified barium titanate ceramics

Donor/acceptor (La/Mn) doped BaTiO3 ceramics, sintered at different temperatures, were studied regarding their microstructure and dielectric properties as well as the dielectric response in a ferroelectric/paraelectric regime. The concentrations of La3+ as donor, ranging from 0.1 to 5.0 at% were used for doping, while a content of Mn4+ as acceptor was at 0.05 at% in all samples. The sintering temperature of codoped samples were 1290? and 1350?C. A reduction in grain size and fine-grained microstructure with average grain size from 0.5 to 2.0 mm was observed in low doped samples, whereas the abnormal growth of individual grains took place in the 2 at% and 5 at% La doped specimens. The dielectric properties of these samples were investigated as a function of frequency (100Hz - 20 kHz) and temperature (20-180?C). The measured results suggested that both the dielectric constants of the ceramics (er at room temperature and ermax at the Curie temperature) decreased as the concentration of La3+ increased. The dielectric permittivity was in the range of 944 to 3200. For samples doped with 0.1 at% La and sintered at 1350?C, the highest dielectric constant value at room temperature (er= 3200) and Curie temperature (er= 5000) were measured. For all measured samples the dissipation factor was less than 0.09. With an increase in La contents, dielectric measurements exhibited shift in the Curie temperature (Tc) towards the low temperature. Using the Curie-Weiss and the modified Curie-Weiss law, Curie's constant C was calculated as well as the parameterg, which describes the deviation from the linear dependence er of T above the phase transformation temperature. The calculated values for g ranged from 1.01 to 1.43. These values indicate a sharp phase transformation in lowdoped and diffuse phase transformation in highly La doped samples. The phase transition was reflected in the values of C that started to decrease with increasing dopant content.

Dielectric Properties of A, B-Site Mn-Doped LaTiO<sub>3+δ</sub>

A-site Mn-doped La1-xMnxTiO3+δand B-site doped LaMnxTi1-xO3+δ(x = 0.1, 0.2) composites were synthesized by conventional solid-state reaction method. The low-frequency complex dielectric properties of the composites were investigated as functions of temperature (77 K ≤ T ≤ 360 K) and frequency (100 Hz ≤ f ≤ 1 MHz), respectively. The dielectric constants of A-site doped samples are higher than that of B-site doped samples. The loss tangents of the low doped samples are much less than that of the high doped samples. The A-site doped composites exhibit intrinsic dielectric response with a dielectric constant of ~40 in the temperature below 250 K. Interestingly, the dielectric constants of B-site doped composites always increased in the temperature range from 77 to 360 K. And it is clearly observed that extraordinarily low dielectric loss tangents appear in LaMn0.1Ti0.9O3+δ, which are much lower than that of LaMn0.2Ti0.8O3+δ. These changes indicate that the doped content can affect the intrinsic dielectric characteristics significantly.

Minority carrier diffusion length, lifetime and mobility in p-type GaAs and GaInAs

Minority carrier diffusion lengths and lifetimes were determined for p-type Ga(1-x)InxAs with an In-content of 0 ≤ x ≤ 0.53 by cathodoluminescence and time-resolved photoluminescence measurements respectively under low injection conditions; the resulting minority carrier mobilities are also reported. Highly p-doped samples (3 × 1018 cm−3) demonstrate a constant minority carrier diffusion length of (5.0 ± 0.7) μm and a constant lifetime of (3.7 ± 0.7) ns for an In-content up to 21%. Lower doped samples (3 × 1017 cm−3), on the other hand, show an increase in minority carrier diffusion length and lifetime with In-content from (6.3 ± 0.2) μm and (6.2 ± 0.5) ns respectively for GaAs to (14 ± 2) μm and (24.4 ± 0.5) ns respectively for Ga0.79In0.21As. Increasing the In-content to 53% results in a drop in the minority carrier diffusion length independently of the p-doping concentration .This is interpreted as a change in the energy of the Shockley-Read-Hall trap levels within the bandgap as a function of indium concentration.

Characterization of n-Type and p-Type Long-Wave InAs/InAsSb Superlattices

The influence of dopant concentration on both in-plane mobility and minority carrier lifetime in long-wave infrared InAs/InAsSb superlattices (SLs) was investigated. Unintentially doped (n-type) and various concentrations of Be-doped (p-type) SLs were characterized using variable-field Hall and photoconductive decay techniques. Minority carrier lifetimes in p-type InAs/InAsSb SLs are observed to decrease with increasing carrier concentration, with the longest lifetime at 77 K determined to be 437 ns, corresponding to a measured carrier concentration of p 0 = 4.1 × 1015 cm−3. Variable-field Hall technique enabled the extraction of in-plane hole, electron, and surface electron transport properties as a function of temperature. In-plane hole mobility is not observed to change with doping level and increases with reducing temperature, reaching a maximum at the lowest temperature measured of 30 K. An activation energy of the Be-dopant is determined to be 3.5 meV from Arrhenius analysis of hole concentration. Minority carrier electrons populations are suppressed at the highest Be-doping levels, but mobility and concentration values are resolved in lower-doped samples. An average surface electron conductivity of 3.54 × 10−4 S at 30 K is determined from the analysis of p-type samples. Effects of passivation treatments on surface conductivity will be presented.

Electrical characteristics of Er doped BaTiO3 ceramics

In this study, the electrical resistivity (?) and PTC effect of Er doped BaTiO3 ceramics are investigated. The concentrations of Er2O3 in the doped samples vary from 0.01 to 1.0 at% Er. The samples are prepared by the conventional solid state reaction, and sintered at 1320? and 1350?C in air atmosphere for 4 hours. The SEM analysis shows that all of measured samples are characterized by polygonal grains. The uniform and homogeneous microstructure with grain sizes from 20 to 45?m is the main characteristic of the low doped samples (0.01 and 0.1 at% Er). For the samples doped with the higher dopant concentration (0.5 and 1.0 at%) the average grains sizes have been ranged from 5 to 10 ?m. The electrical resistivity is measured in the temperature range from 25?C to 170?C, at frequencies 1 kHz, 10 kHz and 100 kHz. The electrical resistivity values, measured at frequency of 1 kHz and room temperature, have been ranged from 1.62?104 ?cm to 4.24?104 ?cm, for samples sintered at 1320?C and from 1.43?104 ?cm to 1.94?104 ?cm, for samples sintered at 1350?C. A nearly flat and stable electrical resistivity-temperature response is characteristic for all samples at the temperature range from 25?C to 120?C. Above this temperature, the electrical resistivity increases rapidly. At 170?C the value of electrical resistivity is ranged 9.84?104 ?cm -1.62?105 ?cm, for Tsin=1320?C, and 6.11?104 ?cm 1.32?105 ?cm, for Tsin=1350?C. The electrical resistivity decreases with concentration increment up to 0.5 at%, while above 0.5 at% it increases. Also, with increasing frequency, ? decreases for a few orders of magnitude.

Effects of electron injection on the magnetic and magnetocaloric behavior of Sr2FeMoO6 double perovskite

With the aim of determining and distinguishing the influence of rare-earth doping on the strength of magnetic interactions, magnetic and magnetocaloric properties of Sr2-xPrxFeMoO6 (x = 0.0, 0.1, 0.2, 0.3) double perovskite were investigated. The X-ray diffraction analysis revealed that all the samples crystallized in a tetragonal structure with I4/mmm space group. The temperature dependent magnetization and Arrott analysis suggested a second order of ferromagnetic phase transition in all the synthesized samples. The competing interaction between the electron injection and steric effect resulted in a non-monotonic evolution of the Curie temperature (TC). In the low Pr doped samples the raising of the Curie temperature is mainly due to the electronic effects while the decrease in TC observed for higher Pr doping (x = 0.3) is attributed to the steric effects. The magnetization was observed to increase with the increasing Pr doping (up to x = 0.2) indicating a progressive increase in cationic ordering. The magnetic entropy change was evaluated from the measurement of isothermal magnetization with respect to the magnetic field at different temperatures. The maximum magnetic entropy change and the relative cooling power were found to increase with the increasing Pr doping (x ≤ 0.2). The tunability of magnetization as well as Curie temperature simply by adjusting the dopant concentration and synthesis conditions makes Sr2FeMoO6 a potential candidate for exploring the new kind of magnetic refrigerants.

SYNTHESIS AND CHARACTERIZATION OF ELECTROCHEMICALLY EXFOLIATED GRAPHENE-MOLYBDOPHOSPHATE HYBRID MATERIALS FOR CHARGE STORAGE DEVICES

A novel electrochemically exfoliated graphene-molybdophosphoric acid nanohybride (EG-MoPA) was prepared via a simple method. Both scanning electron (SEM) and atomic force microscopy (AFM) results show that MoPA clusters are attached to the surfaces of graphene sheets. By changing the mass ratio of EG-MoPA, the morphology of nanohybrid itself can be significantly modulated, from mostly flat graphene like structure at low amount of MoPA to very uneven, wavy surfaces when MoPA is present in higher concentration. The Raman and Fourier transform infra red (FTIR) spectra in conjunction with electrochemical results indicate that strong interaction exists between the components of nanohybride based on charge transfer and electrostatic interaction of graphene sheets and MoPA. The electrochemical performances are improved by synergetic effect of reversible redox properties of MoPA and the double layer capacitance of a high-surface area of the obtained nanohybrides. The higher current capability of EG was achieved by anchoring the small MoPA concentration on the graphene support. The strong bonding of EG with the MoPA prevents acid to dissolve in the electrolyte upon cycling, enabling the stable capacitance behaviour of the low-doped EG sample. The capacitance for the EG doped with the high amount of MoPA was found to be much larger than for EG. However, the obtained capacitance decreases at the beginning of cycling due to the dissolution of excessive amount of surface MoPA, weakly bonded to the graphene support.

The study of relation between variable retention time and channel implantation

In this paper, we investigate a Random Telegraph Signal (RTS) like junction leakage current causing a variable retention time (VRT) problem in Dynamic Random Access Memory (DRAM) cells. With sample devices which have different channel doping concentration, hold times of high leakage state and low leakage state are extracted in diverse storage node bias conditions, and their ratios are analyzed based on a simple equation. The hold time ratio of two states decreases with the increasing bias in high channel doping samples, while it increases in both regular channel doping samples and low channel doping samples.

Dielectric characteristics of donor-acceptor modified BaTiO3 ceramics

Sm/Mn codoped BaTiO3 ceramics were investigated for their microstructure and dielectric characteristics. The powders were prepared by the conventional solid state procedure. The concentration of Sm2O3 as a donor dopant has been kept from 0.1 up to 5.0at%. The content of MnO2 as acceptor was kept constant at 0.05at% Mn in all samples. The specimens were sintered at 1290°C, 1320°C and 1350°C in an air atmosphere for two hours.A mainly uniform and homogeneous microstructure with average grain size ranging from 0.3µm to 2.0µm was observed in low doped samples. In highly doped samples, apart from the fine grained matrix, the appearance of local area with secondary abnormal grains was observed.The dielectric properties were investigated as a function of frequency and temperature. The low doped samples exhibit the high value of dielectric permittivity at room temperature and the greatest change at the Curie temperature. The highest value of dielectric constant (εr=6800) was measured for 0.1Sm/BaTiO3 samples sintered at 1350°C. A nearly flat permittivity-temperature response and lower values of εr were obtained in specimens with 2.0 and 5.0at% additive content. The dielectric constant increases with the increase of sintering temperature. The dissipation factor ranged from 0.01 to 0.22 and decreases with the increase of sintering temperature. The Curie constant (C), Curie-Weiss temperature (T0) and critical exponent of nonlinearity (γ ) were calculated using a Curie-Weiss and modified Curie-Weiss law. The highest value of Curie constant (C=9.06·105K) was measured in 0.1at% doped samples. The Curie constant decreased with increasing dopant content. The γ values, ranging from 1.001 to 1.58, point out the sharp phase transition in low doped samples, and the diffuse phase transition in heavily doped BaTiO3 samples.

The magnetization reversal and high temperature dielectric response in Y1−xHoxFe0.5Cr0.5O3

The structural, magnetic, and dielectric properties of the Y1−xHoxFe0.5Cr0.5O3 (x=0, 0.05, 0.1, 0.3, and 0.5) compounds have been investigated. Rietveld refinement of the XRD patterns shows that the compounds possess orthorhombic perovskite structure. The dual magnetization reversal is observed in the samples with x=0.05 and 0.1, and it vanishes when x≥0.3. Ferromagnetic-like behavior with large coercive fields is observed in all Ho3+ doped YFe0.5Cr0.5O3 samples, indicating a doping induced metamagnetic behavior. This abnormal magnetization behavior can be explained by the antiparallel magnetic coupling between the Ho3+ and the canted Cr3+/Fe3+ moments, as well as the Ho–O–Ho magnetic interaction. The dielectric behavior in the frequency range from 100Hz to 10MHz is investigated. The low doped samples (x=0, 0.05, and 0.1) exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. The dual magnetization reversal under low magnetic field makes these materials attractive candidates for the magnetic dual sensor devices.

Upconversion mechanisms of Er3+:NaYF4 and thermal effects induced by incident photon on the green luminescence

Wide range concentrations of Er3+ doped NaYF4 nanocrystals are synthesized. Upconversion mechanisms are discussed under 976nm NIR laser excitation on the basis of the fluorescence spectra and lifetimes data of Er3+. It is found that the heat induced by incident laser results in an evident increase of the slope of emission from 2H11/2 energy level in the pump power dependence. Emission color of samples is investigated and stable chromaticity under different pump power from low and heavy doping samples are found. In addition, upconversion mechanisms are also investigated under 966nm excitation.