First-principles study of structure,mechanical and optical properties of La-and Sc-doped Y_2O_3

The electronic,mechanical and optical properties of La-and Sc-doped Y_2O_3 were investigated using firstprinciples calculations.Two doping sites of Sc and La in Y_2O_3 were modeled.The calculated values of the energy of formation show that the most energetically favorable site for a La atom in Y_2O_3 is a d-site Y atom,while for Sc a b-site Y atom is the more stable position.The calculated band gap shows a slight decrease with increasing La or Sc concentration.The calculated results for the mechanical and optical properties of Y_(2-x)R_xO_3(R = Sc or La,0x ≤ 0.1875)show that La-or Sc-doped Y_2O_3 would have enhanced strength,and thus an ability of resisting external shocks,and increased hardness and mechanical toughness.These improved mechanical properties are achieved without sacrificing the optical properties of the doped compounds.So the doping of La or Sc in Y_2O_3 is permissible in the preparation of Y_2O_3 transparent ceramics,of course,doping of La or Sc will benefit the sintering of transparent ceramics.     

Structural and optical properties of Dy~(3+):YAlO_3 phosphors for yellow light-emitting diode applications

The spectroscopic properties of a series of Dy~(3+) single-doped and Dy~(3+)/Nd~(3+),Dy~(3+)/Tb~(3+),and Dy~(3+)/Tm~(3+)co-doped YAlO_3(yttrium aluminum perovskite,YAP) phosphors were investigated and compared through the measurements of optical absorption,emission spectra,and fluorescence decay curves.For the Dy~(3+) ion single-doped samples,the intensity of each absorption band increases with an increment in Dy~(3+) ion doping concentration,and the identified strong absorption peak at 447 nm indicates that Dy~(3+):YAP phosphors are suitable to be pumped by a blue laser diode(LD).For all co-doped samples,absorption peaks of Dy~(3+) ion along with some of the absorption bands of Nd~(3+),Tb~(3+),and Tm~(3+) ions are observed.Under 351 and 447 nm excitation,a prominent emission peak at 572 nm was obtained in all the samples,corresponding to Dy~(3+):~4 F_(9/2)→~6 H_(13/2) transition.Here,2 at% Dy~(3+):YAP phosphor exhibits the highest yellow emission intensity under 447 nm pumping.Among the three kinds of Dy~(3+) co-doped phosphors,Dy~(3+)/Tb~(3+):YAP phosphor possesses the dominant yellow emission.The fluorescence decay curves show exponential behaviour and are fitted well.The Commission International de L'Eclairage(CIE)chromaticity coordinates were calculated following the respective emission spectra,and it is found that all the coordinates locate in the yellow region.The energy transfer(ET) processes were investigated and the concentration quenching mechanism was discussed.The obtained results suggest that Dy~(3+)-activated YAP phosphors are good candidates for yellow LED applications.     

Doping effect of rare-earth (lanthanum,neodymium and gadolinium) ions on structural,optical, dielectric and magnetic properties of copper nanoferrites

Copper and rare earth-doped (RE = La, Gd, Nd) CuFe_1.85RE_0.15O₄ nanoferrites were prepared using the sonochemical method. The effective doping of rare-earth (La³⁺, Nd³⁺, Gd³⁺) ions with copper nanoferrites was confirmed by X-ray diffraction. The tetrahedral and octahedral sites of the nanoferrites were identified through the Fourier transform infrared spectra. The doping of rare-earth elements enhances the optical bandgap energy of the nanoferrites that are observed through Ultraviolet–DRS spectra. The oxidation state of the elements Cu 2p, La 3d, Nd 3d, Gd 3d, Fe 2p and O 1s was analyzed. Scanning electron microscopy images indicate a spherical morphology with agglomeration to some elongate. The values of dielectric constant and conductivity decrease considerably due to doping rare-earth ions in copper nanoferrites. Low saturation magnetization and high coercivity values of rare earth-doped copper nanoferrites are observed from the typical hysteresis curves.     

Tb~(3+) substituted strontium hexaferrites:Structural,magnetic and optical investigation and cation distribution

In this study,SrFe_(12-x)Tb_xO_(19)(0.00≤x≤0.1) hexaferrites(HFs) were prepared successfully by citrate solgel approach.X-ray powder diffraction analyses affirm the hexagonal structure of products.Impurity phase starts to appear for x≥0.04.The crystallites sizes were estimated to be in the range of 33-46 nm.All the products exhibit inhomogeneous distribution of grain size detected through SEM.The analyses of magnetization versus applied magnetic field,M(H),were performed.Magnetization measurements were done at room(300 K;RT) and low(10 K) temperatures.The different magnetic parameters including saturation magnetization M_s,remanence M_r,squareness ratio(SQR=M_r/M_s),coercivity H_c,and magnetic moment n_B are deduced and discussed in detail.At both considered temperatures,M(H) results show ferrimagnetic nature for all compositions.It is shown that the Tb substitutions significantly affect M(H)data.A significant increase in the M_s,M_r,and n_B is observed for x=0.02 sample.The SQR values are around 0.5 indicating the single domain nature with uniaxial anisotropy.The obtained magnetic results were investigated deeply with relation to structural and microstructural properties.Mossbauer spectroscopy results were also investigated.According to Mossbauer results,the Tb~(3+) ions preferentially occupy 12 k and 4f_2 sites.     

Mechanism for transmittance light tunable property of nanocrystalline Eu-doped SmB_6:Experimental and first-principles study

Binary nanocrystalline rare-earth hexaboride is regarded as one of the promising optical absorption materials that possess the high transparency for visible light and the strong absorption for NIR due to the effects of localized surface plasmon resonance.In present work,we experimentally investigated the structural and optical absorption of ternary nanocrystalline Eu-doped SmB_6 powder.As a result,it is found that the reaction temperature as an important factor not only refines the grain size,but also improves the powder dispersion of synthesized samples.The optical absorption results reveal that the transmittance wavelength of nanocrystalline SmB_6 increases from 696 nm to exceeding 1000 nm with the Eu doping content increasing to x=0.8.Theo retically,in order to study the transmittance wavele ngth tunable mechanisms of nanocrystalline Eu-doped SmB_6,the electronic structure,density of states and energy loss function were calculated by first-principle calculation.It shows that the En~(2+) doping into SmB_6 effectively reduces the plasma frequency excitation energy from 1.48 to 1.25 eV and leads to the transmittance wavelength redshift toward a higher wavelength.Based on above meaningful studies,present work is helpful for extension of optical applications of nanocrystalline SmB_6 powder.     

Transparent perovskite glass-ceramics for visual optical thermometry

Optical thermometers have aroused considerable attention in recent years,and the increasing demand of sensitivity for practical application encourages the investigation on developing innovative non-contact optical thermo metric materials with higher sensitivity and accuracy.Perovskite quantum dots(QDs)with excellent temperature-dependence optical properties,provide a feasible approach to realizing the detection of temperature change,however,their poor high temperature thermal stability and the facile realization to obtain the production remain a daunting challenge.Herein,growing Tb~(3+)-doped CsPbl_3 QDs in situ in borosilicate glass is proposed,which ensures the phase stability,and high-efficiency florescence output of the all-inorganic perovskite as a temperature sensor.A higher absolute and relative temperature sensitivity(0.0398 K~(-1) and 7.12%/K,respectively),along with the visible color change from orange-red to yellow-green with the increase of temperature is accomplished.Notably,the repeatable florescence intensity of Tb~(3+)-doped CsPbl_3 QDs under high temperature enables their temperature sensing application.     

Preparation and magnetic properties of anisotropic Nd_2Fe_(14)B/Sm_2Co_(17) hybrid-bonded magnets

In the present work, anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets were prepared with different Nd-Fe-B contents. It is found that the particle distributions and ratios between the two magnetic phases have important roles in the magnetic properties, microstructures and thermal stability of the magnets. With increase of Nd-Fe-B content, the saturation magnetization of the anisotropic hybrid magnet increases significantly, however, coercivity decreases, and the demagnetization curves show magnetically single-phase behavior. The anisotropic Nd_2 Fe_(14) B/Sm_2 Co_(17) hybrid-bonded magnets exhibit a maximum energy product and remanence of 14.15 MGOe and 99.53 A·m~2/kg, respectively, when the NdFe-B content is 70 wt% at room temperature. Furthermore, the hybrid magnets also have better thermal stability at elevated temperatures due to the interaction between the two magnetic particles.     

Evolution of microstructures and optical properties of gadolinium oxide with oxygen flow rate and annealing temperature

In this study, the effects of oxygen flow rate and annealing temperature on Gd_2 O_3 structures and optical properties were systematically analyzed. Gd_2 O_3 films were deposited on both quartz and ZnS substrates by magnetron sputtering and then annealed under vacuum at 700, 800 and 900℃, Restructure and phase transformation from cubic to monoclinic occur at different temperatures depending on the oxygen flow rate. The optical band gap, which is more sensitive to the annealing temperature than oxygen flow rate changes from 5.32 to 5.65 eV. The refractive index is approximately 1.75 at 550 nm and is adjustable by the oxygen flow rate. The transmittance of the ZnS substrate with Gd_2 O_3 film exceeds 80% and reaches82% at the 7.5-9.5 μm range. When ZnS is coated on both sides, the transmittance is increased to approximately 90%. Our results indicate that Gd_2 O_3 films are promising new candidates for anti-reflective coatings in the infrared region.     

First-principles study of electronic structure and optical properties of Er:Lu_2O_3

In the present computational study,we found that Er:Lu₂O₃materials have promise for application in laser applications.The crystal structure and the electronic and optical properties of Er:Lu₂O₃materials were studied using first-principle calculations under the framework of density functional theory.Based on the experimental and calculated results,the structure of Lu₂O₃was established.The calculated results show that doping by Er³⁺can effectively improve its absorption coefficient in the ultraviolet region and improve the static dielectric constant of Lu₂O₃.As the doping concentration of Er³⁺increases,the energy of the valence band electrons excited to the conduction band decreases,and the transition is more likely to occur.The absorption coefficient,reflectance,and electron energy loss spectroscopy are bathochromic shifted.The Lu_2-xEr_xO₃(02O₃.     

Effect of fluxes on synthesis and luminescence properties of BaSi2O2N2:Eu2+ oxynitride phosphors

Eu²⁺ activated BaSi₂O₂N₂ oxynitride bluish-green phosphor was synthesized adopting conventional high-temperature solid-state reaction method, in which BaF₂, Na₂CO₃ and NH₄Cl were used as the fluxes. The phase formation, size distribution and microscopic morphology were characterized to investigate the influence of adding fluxes on photoluminescence properties. The results indicate that with the addition of BaF₂ flux, the particle morphology becomes regular and size distribution narrows and the phase purity of BaSi₂O₂N₂:Eu²⁺ phosphor can be improved effectively. The photoluminescence intensity of BaSi₂O₂N₂:Eu²⁺ phosphor with BaF₂ as flux gets enhanced obviously, which is much higher than that of Na₂CO₃, NH₄Cl and without flux. The optimum content of BaF₂ flux is 4 wt%, and the maximum photoluminescence intensity of the BaSi₂O₂N₂:Eu²⁺ phosphor prepared with BaF₂ flux rises to 141%, meanwhile, the phosphors with BaF₂ flux exhibits low thermal quenching. The results indicate that the BaSi₂O₂N₂:Eu²⁺ is sort of promising bluish-green phosphor for application in full-spectra LED.     

Effect of Nb~(5+) and Cu~(2+) codoping on thermal properties of Gd_2Zr_2O_7 ceramic

In this work,Nb⁵⁺and Cu²⁺were selected to partially substitute Zr4+in Gd₂Zr₂O₇for studying the phase structure,microscopic morphology and thermal properties.Gd₂(Zr_(1-3 x/2)Nb_xCU_x/2)₂O₇(x=0,0.05,0.1,0.15,0.2,0.25)ceramic materials were synthesized by high-temperature solid-state reaction method.The results show that the Gd₂(Zr_(1-3 x/2)Nb_xCu_x/2)₂O₇ceramics present cubic pyrochlore structure with clear grain boundaries and dense cell structure.And the thermal expansion coefficient of Gd₂(Zr_(1-3 x/2)Nb_xCu_x/2)₂O₇ceramics gradually decreases because of the incorporation of Nb⁵⁺and Cu²⁺into Zr-site in Gd₂Zr₂O₇.Meanwhile,its thermal conductivity decreases firstly and then increases with the doping of Nb⁵⁺and Cu²⁺,which reaches the lowest value for the composition of Gd₂(Zr_0.85Nb_0.1Cu_0.05)₂O₇.     

Sub-10 nm lanthanide-doped SrFCl nanoprobes:Controlled synthesis,optical properties and bioimaging

Alkaline-earth dihalide nanocrystals(NCs) such as SrFCl, owing to their high chemical stability and low phonon energy, are excellent host materials for lanthanide(Ln~(3+)) doping to achieve desirable optical properties for various bioapplications, Herein, we report a novel strategy for the synthesis of sub-10 nm Ln~(3+)-doped SrFCl NCs with efficient upconverting and downshifting luminescence through a facile onestep hot-injection method. Utilizing the temperature-dependent upconverting luminescence(UCL) from the thermally coupled ~2H_(11/2) and ~4S_(3/2) levels of Er~(3+), we showed the potential of SrFCl:Yb,Er NCs as sensitive UCL nanoprobes for non-contact thermal sensing with a maximum detection sensitivity of 0.0066 K~(-1), which is among the highest values for thermal sensing based on Er~(3+)-activated UCL nanoprobes. Furthermore, by employing the intense downshifting luminescence from Tb~(3+) and Eu~(3+), we demonstrated the successful use of biotinylated SrFCl:Ce,Tb and SrFCl:Eu~(3+) nanoprobes for biotin receptor-targeted cancer cell imaging, thus revealing the great promise of SrFCl:Ln~(3+) nanoprobes for versatile bioapplications.     

Structural properties and catalytic performance of the LaCuZn mixed oxides for CO2 hydrogenation to methanol

A series of La-Cu-Zn-O mixed oxide catalysts were synthesized by a co-precipitation method and calcined under different temperatures. The XRD, BET, TPR, N_2 O-adsorption, XPS, SEM and TPD techniques were carried out to measure the aimed catalysts. The results indicated that the chemical environment of lanthanum element changes with the increase of calcination temperature. The La_2 CuO_4 perovskite structure is obtained at the temperature higher than 823 K and the special copper species appear in the perovskites due to the special structure property. The catalysts with La_2 CuO_4 perovskite structure show higher methanol selectivity compared with the mixed copper catalyst. For the perovskite catalysts, the conversion of CO_2 changes with the same tendency of the copper species ratio((Cu~(α+)+Cu~0)/(Cu_(Total))%), which implied both Cu~(α+) and Cu~0 are important active sites in the perovskite catalyst for the reaction.     

Synthesis and optical characterization of Eu2+,Tb3+-codoped Sr3Y(PO4)3 green phosphors

A series of Eu~(2+),Tb~(3+)-codoped Sr_3 Y(PO_4)_3(SYP) green phosphors were synthesized by hightemperature solid-state reaction. Several techniques, such as X-ray diffraction, UV-vis spectrum,and photoluminescence spectrum, were used to investigate the obtained phosphors. The present study investigates in detail photoluminescence excitation and emission properties, energy transfer between the two dopants, and effects of doping ions on optical band gap. SYP:0.05 Eu2+ phosphor shows an intense and broad excitation band ranging from 220 to 400 nm and exhibits a bright green emission band with CIE chromaticity coordinates(0.189, 0.359) under 350 nm excitation. Green emission of SYP:0.03 Tb3+ is intensified by codoping with Eu~(2+), and energy transfer mechanism between them is demonstrated to be a dipole-dipole interaction. Upon 350 nm excitation, SYP:Eu~(2+),Tb~(3+) phosphors exhibits two dominating bands peaking at 466 and 545 nm, which are assigned to 4 f~65 d~1→4 f~7 transition of Eu~(2+) ions and ~5 D_4→~7 F_5 transition of Tb~(3+) ions, respectively. Optimal doping concentrations of Eu~(2+) and Tb~(3+) in the SYP host are 5 mol% and 15 mol%, respectively. Results indicate that SYP:Eu~(2+),Tb~(3+) phosphors are potentially used as green-emitting phosphors for white light-emitting diodes.     

Tunable emission,energy transfer and thermal stability of Ce3+, Tb3+ co-doped Na2BaCa(PO4)2 phosphors

A series of single Ce³⁺ doped and Ce³⁺ and Tb³⁺ co-doped Na₂BaCa(PO₄)₂ (NBCP) phosphors was synthesized by conventional solid-stated reaction method. The crystal structure, luminescence properties, thermal stability and energy transfer were carefully investigated. Ce³⁺ is inferred to substitute the Ba²⁺ site in NBCP lattice. The color-tunable emission from blue to green is observed by adjusting Tb³⁺ concentration among NBCP:0.03Ce³⁺,yTb³⁺ phosphors. The energy transfer behavior from Ce³⁺ to Tb³⁺ ions is both illustrated by co-doped PL spectra and decay curves. The energy transfer efficiency is as high as 91.5%. The mechanism of energy transfer is resonance type of dipole-dipole transition. In this work, the optimal phosphor exhibits the excellent thermal stability which keeps at 94.9% of that initial value at room temperature when temperature reaches to 150 °C. The Ce³⁺ and Tb³⁺ co-doped NBCP phosphor is a promising candidate for the application in the general lighting and display fields.     

La~(3+) doped LiCo_(0.25)Zn_(0.25)Fe_2O_4 spinel ferrite nanocrystals:Insights on structural,optical and magnetic properties

This paper addresses the manipulation of structural,morphology,optical and magnetic properties of LiCo_(0.25)Zn_(0.25)Fe_2 O_4 ferrite via incorporation of different proportions of La~(3+) at the expense of iron ions using a sol-gel method.The samples were characterized using the X-ray diffraction technique(XRD),Fourier transform infrared(FT-IR) spectroscopy,the energy dispersive X-ray spectra(EDX),inductively coupled plasma optical emission spectroscopy(ICP-OES),high resolution scanning electron microscopy(SEM),Brunauer-Emmett-Teller(BET) surface area analysis,ultraviolet-diffuse reflectance spectroscopy(UV-DRS),and vibrating sample magnetometer(VSM) technique.The Rietveld refinements of the samples indicate that at higher concentrations of La3+,nanostructures with dual phase,i.e.cubic spinel and orthorhombic LaFeO_3 perovskite with space group(Pbnm) appear.Optical studies show that the energy band gap(E_g) of the bare LiCo_(0.25)Zn_(0.25)Fe_2 O_4 ferrite sample(2.18 eV) reaches up to 2.47 eV at x=0.06 and above this concentration,it drops sharply to 2.00 eV.Although the saturation magnetization and the coercivity of LiCo_(0.25)Zn_(0.25)La_xFe_(2-x)O_4 are lower than that of LiCo_(0.25)Zn_(0.25)Fe_2 O_4 NPs.Overall,the superparamagnetic nature and low values of saturation magnetization and coercivity of LiCo_(0.25)Zn_(0.25)La_xFe_(2-x)O_4 NPs are suitable to be applied in transformers core.     

Spectroscopic properties of Er3+-doped fluoroindate glasses

The optical and thermal properties of a new class of fluoroindate glass with different erbium contents were investigated via Raman, transmission, and fluorescence spectroscopies, fluorescence decay curve analysis, and differential scanning calorimetry. The strength parameters of the samples were calculated using the Judd–Ofelt theory. The mid-infrared luminescence properties of erbium-doped fluoroindate glasses were studied, and a strong emission at 2.7 μm was obtained. Compared with the traditional ZBLAN glass, this glass has excellent emission properties, especially a longer fluorescence lifetime (7.09 ms) and larger emission cross-section (6.95 × 10^?21 cm²) at 2.7 μm. The results indicate that fluoroindate glass is an attractive host for mid-infrared lasers and as a gain medium for optical amplifier applications.     

Luminescence properties of Pr3+ and Bi3+ co-doped NaCaTiNbO6 phosphor for red-LEDs

This paper investigates the photoluminescence properties of NaCaTiNbO_6:Pr~(3+) and NaCaTiNbO_6:Pr~(3+),Bi~(3+) phosphors. NaCaTiNbO_6:Pr~(3+) and NaCaTiNbO_6:Pr~(3+),Bi~(3+) powder were synthesized successfully by solid state reaction method. Phase purity was checked using X-ray powder diffractometry(XRD). The excitation and emission spectra were recorded to elucidate the photoluminescence properties of NaCaTiNbO_6:Pr~(3+) and NaCaTiNbO_6:Pr~(3+),Bi~(3+). Furthermore,fluorescence lifetime measurements were performed. The excitation spectra of NaCaTiNbO_6:Pr~(3+) show a main band centered at around 357 nm.The luminescence spectra of NaCaTiNbO_6:Pr~(3+) exhibit a red emission peak at 615 nm from the ~1 D_2→~3 H_4 transition of Pr~(3+) ions. With the introduction of the Bi~(3+) ion into NaCaTiNbO_6:Pr~(3+), the luminescence intensity is enhanced nearly two times. Meanwhile,the absorption band edge of NaCaTiNbO_6:Pr~(3+) is shifted from 380 to 420 nm. Thus, this study shows that the red phosphor NaCaTiNbO_6:Pr~(3+) incorporated with Bi~(3+) is advantageous for light-emitting diode applications.     

Synthesis,upconversion luminescence and optical heating of hexagonal NaGdF4:Yb3+,Er3+

An optical heater based on hexagonal NaGdF_4:Yb~(3+)/Er~(3+) is reported. XRD, SEM and EDS characterization results show that F~-/Ln~(3+) can not only control the phase composition, particle size and morphology, but also affect the effective doping concentration of Yb~(3+) and Er~(3+).When F~-/Ln~(3+) is 12/1, the strongest upconversion luminescence is obtained. Based on the luminescent temperature sensing behavior of Er~(3+),the photo-thermal conversion performance was investigated. The results indicate that the temperature of irradiation spot is linearly dependent on the power density, and the photo-thermal responsivity is determined to be 3.3K·cm~2/W. Also, it is found that the photo-thermal conversion efficiency can be regulated by changing the Yb~(3+) doping concentration. Compared with the nano-gold, copper sulfide and carbon nanotubes, the NaGdF_4:Yb~(3+)/Er~(3+) has the triple functions of upconversion luminescence, temperature sensing, and photo-thermal conversion, and may therefore be a promising optical heater for photo-thermal therapy of tumors.     

Improvement of coercivity and thermal stability of Nd-Fe-B sintered magnets by intergranular addition of Tb80Fe20 alloy

To improve the coercivity and temperature stability of Nd-Fe-B sintered magnets for high-temperature applications, the eutectic Tb₈₀Fe₂₀ (wt%) alloy powders were added into the Nd-Fe-B sintered magnets by intergranular method to enhance the coercivity (H_cj) and thermal stability. The microstructure, magnetic properties and thermal stability of the Nd-Fe-B magnets with different Tb₈₀Fe₂₀ contents were studied. The experimental results demonstrate that the coercivity (H_cj) of the sintered Nd-Fe-B magnet is significantly enhanced from 14.12 to 27.78 kOe, and the remanence (B_r) decreases not obviously by introducing 4 wt% Tb₈₀Fe₂₀ alloy. Meanwhile, the reversible temperature coefficients of coercivity (β) and remanence (α) of the Nd-Fe-B magnets are increased from ?0.5634%/℃ to ?0.4506%/℃ and ?0.1276%/℃ to ?0.1199%/℃ at 20–170 ℃, respectively. The Curie temperature (T_C) of the Nd-Fe-B magnet is slightly enhanced with the increase of Tb₈₀Fe₂₀ content. Moreover, the irreversible flux magnetic loss (h_irr) is obviously reduced as Tb₈₀Fe₂₀ addition increases. Further analysis of the microstructure reveals that a modified microstructure, i.e. clear and continuous RE-rich grain boundary layer, is acquired in the sintered magnets by introducing Tb₈₀Fe₂₀ alloy. The associated mechanisms on improved coercivity and thermal stability were comprehensively researched.