Spectroscopic investigations on Yb~(3+) doped and Pr~(3+)/Yb~(3+) codoped tellurite glasses for photonic applications

In this work we repo rt on structural and spect roscopic properties of Yb3+doped and Pr~(3+)/Yb~(3+)co-doped TeO_2-Bi_2 O_3-ZnO-Li_2 O-Nb_2 O_5(TBZLN) tellurite glasses.Bending and stretching modes of TeO_2 and Te-OH bond(strong and weak) were analysed from the deconvolution of observed Raman and FT-IR spectra.Based on the absorption measurements,the energy bands of Yb~(3+)and Pr~(3+)ions are assigned.The spectroscopic properties for the radiative transitions of Yb~(3+)and Pr~(3+)ions were reported using McCumber and Judd-Ofelt theories.Visible emission bands originating from ~3 P_1 and ~3 P_0 to lower lying levels of Pr~(3+)were registered under 447 nm excitation.The emission band around 1334 nm assigned to the Pr~3:~1 G_4→~3 H_5 was observed when excited at 980 nm.The stimulated emission cross-section(σ_(emi)(λ))and effective linewidth(Δλ_(eff)) for the ~3 P_1→~3 H_6,~3 P_1→~3 H_5,~3 P_0→~3 H_6,~3 P_0→~3 F_2,~3 P_1→~3 F_3,~3 P_1→~3 F_4,~3 P_0→~3 F_4 and ~1 G_4→~3 H_5 transitions of Pr~(3+)are reported.Upconversion luminescence in Pr~(3+)/Yb~(3+)codoped glass upon 980 nm excitation was measured.Possible resonant transfer processes between Yb~(3+)and Pr~(3+)ions are presented and discussed.The chromaticity co-ordinates were also evaluated from the visible emission spectra showing that Pr~(3+)/Yb~(3+)co-doped glass may be suitable for the development of yellow-orange(λ_(exc)=447 nm) and near white light(λ_(exc)=980 nm) emitting devices in photonics.     

Effect of acceptor ions concentration in lead phosphate glasses co-doped with Tb~(3+)-Ln~(3+)(Ln=Eu,Sm)for LED applications

In this work,lead phosphate glasses doubly doped with Tb~(3+) and Ln~(3+)(Ln=Eu,Sm) ions were prepared.The excitation and emission spectra of lanthanides ions were recorded.The luminescent properties of lead phosphate glasses containing various concentrations of acceptor ions were analyzed.It is observed that luminescence bands corresponding to characteristic transitions of rare earth ions are present on emission spectra measured under direct excitation of Tb~(3+).From the emission spectra,the Commission Internationale de I'Eclairage(CIE) chromaticity coordinates(x,y) were calculated in relation to potential application studied systems for white LEDs.Luminescence lifetimes were also determined based on decay measurements and discussed in details.In general,the luminescence spectra and luminescence lifetimes depend on the relative concentrations of the optically active dopants.     

Effect of chloride on spectrum properties of Pr~(3+)/Ho~(3+) co-doped fluorozirconate glasses

An effective method of improving the luminescent properties of rare earth ions in fluoride glasses were reported.The Pr~(3+)/Ho~(3+)co-doped fluorochlorozirconate luminescent glasses were prepared,and the effects of chloride on the spectral properties and structure of the glasses were studied.According to the results,the glass stability is improved,and the luminescence intensity in the visible range is significantly enhanced with the introduction of chloride.By introducing 7.5 mol% BaCl_2,the luminescence intensity reaches the maximum and increases by three times,The mechanism of luminescence enhancement is explained by analyzing the correlation between the composition and the structure.The chloride ions disperse outside the glass network before the introduction of 7.5 mol% BaCl_2 and increased dispersity of Pr~(3+)and Ho~(3+)ions in the fluorozirconate glasses.     

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.     

Growth and optical properties of ytterbium and rare earth ions codoped CaF_2-SrF_2 eutectic solid-solution(RE=Y~(3+),Gd~(3+),La~(3+))

Ytterbium and rare earth ions(RE=Y,Gd,La)codoped CaF₂-SrF₂single crystals(3 at%Yb,6 at%RE:CaF₂-SrF₂)were fabricated by temperature gradient technology(TGT).All the space groups remain the same Fm3m as that of Yb:CaF₂-SrF₂.The lattice parameter a,unit cell volume V,as well as bond length of Ca/Sr-F and F-F increase in the sequence of rare-earth ions radius Y³⁺3+3+.The segregation coefficients of Yb ions are 0.87 in Yb,La:CaF₂-SrF₂and Yb,Gd:CaF₂-SrF₂,which are larger than 0.85 in Yb,Y:CaF₂-SrF₂and 0.80 in Yb:CaF₂-SrF₂.Absorption spectra in the range of 200 and 400 nm were analysed with Yb²⁺contents.The absorption and emission cross-sections in the range of 900-1100 nm were determined together with fluorescence lifetime.The saturation pump density/Sat,minimum pump density/m in and gain cross-section were analysed.Yb,La:CaF₂-SrF₂has a relatively higher optical parameter(δem×t,0.52×10²⁰cm²·ms),lower Isat(3.68 kW/cm²)and^min(0.50 kW/cm²)at 1038 nm indicating the potential application in high power laser.Low phonon energy of CaF₂-SrF₂is 302 cm^-1which is located between those of CaF₂and SrF₂as measured by Raman spectra.It is believed that ytterbium and rare earth ions(RE=Y³⁺,Cd³⁺,La³⁺)codoped CaF₂-SrF₂eutectic solid-solution is promising for high-power and wavelength-tunable solid-state lasers.     

Luminescence and energy transfer of color-tunable Lu_2MgAl_4SiO_(12):Eu~(2+),Ce~(3+),Mn~(2+) phosphors

Energy transfer among the co-doped activators is an efficient route to achieve color-tunable emission in inorganic phosphors.Herein,photoluminescence tuning from blue to cyan has been achieved in the Lu2MgAl4 SiO12;Eu^2+,Ce^3+phosphors by varying the Ce^3+concentration with a fixed Eu^2+content.With the further introduction of a Mn^2+-Si^4+couple into the host lattice,the emission color can be tuned to red through the energy transfer of Eu^2+and Mn^2+.The luminescence properties and the energy transfer mechanism were studied in detail.The energy transfer from Eu^2+to Ce^3+is certified as a dipolequadrupole interaction with the energy transfer efficiency of 41.4%and Eu^2+to Mn^2+belongs to a dipole-dipole interaction with the energy transfer efficiency of 94.3%.The results imply that this singlephased Lu2MgAl4 SiO12:Eu^2+,Ce^3+,Mn^2+phosphor has a potential prospect for application in near-UV chip pumped white light emitting diodes.     

Enhanced photocatalytic activity of Gd~(3+) doped TiO_2 and Gd_2O_3 modified TiO_2 prepared via ball milling method

Gd~(3+)/TiO_2 and Gd_2O_3/TiO_2 nanoparticles were prepared by ball milling method.The effects of Gd~(3+)ion and Gd_2O_3 on the structure and optical property of TiO_2 were studied by XRD and UV-vis DRS.Specific surface area was determined by Brunauer-Emmett-Teller(BET)method.The morphology and elemental composition were characterized by SEM-EDS.XPS was used to determine the surface compositions and chemical character of elements.The sample sizes and microstructures were observed by TEM.The photocatalytic activities of TiO_2 nanoparticles modified with rare earth metal gadolinium(Gd~(3+)ion or Gd_2O_3)were evaluated by degradation of methylene blue(MB)under UV light.Experimental results indicate that 2,5 mol%Gd~(3+)/TiO_2 shows the best photocatalytic activity compared with Gd_2O_3/TiO_2 and pure TiO_2.The existence of gadolinium can exhibit the aggregation and induce lattice distortion of TiO_2 obtained from XRD,SEM and TEM results.The band gap energy of 2.5 mol%Gd~(3+)/TiO_2 decreases to3.07 eV and it leads to visible light absorption response which can be seen from UV-vis absorption spectra.The surface area of 2.5 mol%Gd~(3+)/TiO_2 equals to 85.8 m~2/g and average crystal size is 21.1 nm.EDS and XPS analyses reveal that gadolinium can be introduced either into TiO_2 lattice or adsorbed on the surface of TiO_2.The content of surface OH groups in 2.5 mol%Gd~(3+)/TiO_2 is 50,88%(1.55 times higher than that of pure TiO_2)and the content of lattice oxygen decreases to 11.26%.The MB(25 mg/L)degradation reaction rate constants of 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2 were0.0713,0.0588 and 0.0263 min~(-1),respectively.The degradation rates of rhodamine B(30 mg/L)in 60 min are 97,9%,90.1%and 84.6%for 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2,respectively.     

Influence of Y~(3+),Yb~(3+),Gd~(3+) cations on structural and electromagnetic properties of CuFe_2O_4 nanoferrites prepared via one step sol-gel method

Rare earths(REs) play a key role in distorting spinel structure by creating some defects at the lattice sites and make them suitable for magnetodielectric applications.In the present study,the nanoferrites of CuRE_(0.02)Fe_(1.98)O_4,where REs=Y~(3+),Yb~(3+),Gd~(3+),were prepared using one step sol-gel method.The prepared samples are copper ferrite(CFO),yttrium doped copper ferrite(Y-CFO),ytterbium doped copper ferrite(Yb-CFO) and gadolinium doped copper ferrite(Gd-CFO),respectively.The single-phase structure of all the REs doped nanoferrites was determined by X-ray diffraction(XRD) analysis.The porosity,agglomerations and grain size of the REs doped copper ferrite were examined using field emission scanning electron microscopy(FESEM) analysis.Fourier transform infrared spectroscopy(FTIR)elaborates the phase formation and environmental effects on the REs doped nanoparticles(NPs).The recorded room temperature M-H loops from a vibrating sample magnetometer(VSM) elucidate the magnetic properties of the REs doped spinel nanoferrites.The magnetic saturation(M_s) was calculated in the range of 23.08 to 51.78 emu/g.The calculated coercivity values(272.6 to 705.60 Oe) confirm the soft magnetic behavior of REs doped copper ferrites.Furthermore,the electromagnetic and dielectric properties were assessed using a Vector network analyzer(VNA) from 1 to 6 GHz.The permeability,permittivity,dielectric tangent loss and electric modulus of the REs doped spinel ferrites illustrate that the prepared NPs may be suitable for microwave and high frequency applications.     

Luminescence tuning of Ce~(3+),Pr~(3+) activated(Y,Gd)AGG system by band gap engineering and energy transfer

Tuning of phosphor luminescence properties,including the emission energy/intensity and thermal stability,is an important way to develop superior luminescent materials for diverse applications.In this work,we discuss the effect of band gap engineering and energy transfer on the luminescence properties of Ce^3+or Pr^3+doped(Y,Gd)AGG systems,and analyze the underlying reasons for their different phenomena.By using VUV-UV excitation spectra and constructing VRBE schemes,the changes of host band structure,5 d excited level energies and emission thermal stability of Ce^3+and Pr^3+with the incorporation of Gd^3+ions were studied.In addition,the energy transfer dynamics was also investigated in terms of the luminescence decay curves.This work demonstrates a way to tune phosphor luminescence properties by combining band gap engineering and energy transfer tailoring and provides an inspiring discussion on the different results of Ce^3+doping on the Ce^3+and Pr^3+emissions.     

Luminescent and thermometric properties of dual emitting Eu~(2+)/Sm~(3+) co-doped Sr_4La(PO_4)_3O phosphor based on energy transfer

Eu²⁺/Sm³⁺co-doped dual-emitting Sr₄La(PO₄)₃O phosphors were synthesized through a convenient high temperature solid state reaction in reductive atmosphere.The structure,luminescence,energy transfer and temperature-dependent luminescence properties of Eu²⁺/Sm³⁺co-doped Sr₄La(PO₄)₃O phosphors were researched and analyzed in detail.The blue emission of Eu²⁺and the red emission of Sm³⁺can work together as FIR signals.Based on the different response characteristics of these two ion emissions to temperature,Sr₄La(PO₄)₃O:Eu²⁺/Sm^(³⁺)phosphor achieves the relative sensitivity of0.48384%/K and a wide range of temperature measurements from room temperature to 573 K.The results reveal that the Sr₄La(PO₄)₃O:Eu²⁺/Sm³⁺phosphor has application prospect in the field of high temperature optical thermometry.The energy transfer mechanism is proved to be the dipole-dipole interaction between Eu²⁺and Sm³⁺ions.     

Systematic study of Nd~(3+) on structural properties of ZnO nanocomposite for biomedical applications; in-vitro biocompatibility,bioactivity, photoluminescence and antioxidant properties

Owing to the inconformity in ionic radius between Nd~(3+) and Zn~(2+), the successful incorporation of Nd~(3+) ion into the ZnO nanocrystals still remains a great challenge. In the present study various doping ratios containing 1 wt%, 5 wt%, 7 wt% and 10 wt% of Nd~(3+) doped ZnO nanoparticles(Nd/ZnO NPs) were synthesized in which a bio-layer caped the NPs. SEM/EDX analysis was performed on the ZnO and Nd/ZnO NPs. In addition, the as-synthesized NPs were characterized using X-ray diffraction(XRD), dynamic light scattering(DLS), differential reflectance spectroscopy(DRS) and photoluminescence(PL) spectroscopy.The average size of Nd(5 wt%)/ZnO NPs was in the range of 6.22 and 15 e18 nm based on XRD and SEM techniques, respectively. The measured band gap values for pure ZnO and Nd/ZnO NCs with doping ratios of 1 wt%, 5 wt%, 7 wt% and 9 wt% were equal to 3.46, 3.26, 3.05, 3.25 and 3.29, respectively. After inhalation, nanoparticles first interact with lung surfactant system and accordingly their toxic effects will appear on lungs cells such as A549 cell line. The effect of Nd/ZnO NPs to interact by human A549 cell line was evaluated by means of cell viability test. According to cell viability test the concentrations of 0.3 and 0.5 mg/mL of Nd/ZnO NPs induce a low toxicity. The present study shows that these toxic effects of Nd/ZnO NPs can be rectified by capping its surface via the addition of a bio-layer around particles in order to prevent them from interacting A549 cell line.     

Effect of doping of different rare earth (europium,gadolinium, dysprosium and neodymium) metal ions on structural,optical and photocatalytic properties of LaFeO3 perovskites

Different rare earth substituted perovskites LaRE_xFe_(1-x)O_3(where RE=Eu~(3+),Gd~(3+),Dy~(3+),Nd~(3+)and x=0.02,0.04,0.06,0.08,0.1) with orthorhombic structure and narrow band gaps were successfully fabricated via sol-gel autocombustion method.All the substituted perovskites are found to exhibit excellent photocatalytic activity towards the oxidative degradation of dye molecules.An excellent increase in the rate constant values of pure perovskite(LaFeO_3) photocatalytic reactions is observed with the substitution of rare earth metal ions.Best results are obtained for LaNd_(0.1)Fe_(0.9)O_3 which exhibits around 7 times increase in the rate constant values for degradation reaction of SO(1.76×10~(-1) min~(-1))and RBY(1.69×10~(-1) min~(-1)) dyes.     

Effects of annealing temperature and neodymium concentration on structural and photoluminescence properties of Nd~(3+)-doped Y_2O_3-SiO_2 powders

We report the structural and photoluminescence(PL) properties of Nd~(3+)-doped Y_2 O_3-SiO_2 powders(Y_2 O_3-SiO_2:Nd~(3+)) as functions of annealing temperature and Nd~(3+) ion doping concentration.Y_2 O_3-SiO_2:Nd~(3+)powders were prepared using the high-energy ball-milling(HEBM) method,and their structural and PL properties were investigated using X-ray diffraction(XRD),Fourier transform infrared(FTIR) spectroscopy,and PL spectroscopy.The XRD results reveal a cubic phase without impurities,and the peak broadening decreases with an increase in annealing temperature due to the increase in the crystallite size.The PL emission intensity increases with an increase in annealing temperature.The highest PL emission intensity is observed for the 300-min milled mixture annealed at 1000℃ for 1 h with a Nd~(3+) concentration of 1 mol%.The PL peaks excited by 800 nm radiation were detected,centered at 1080 nm(~4 F_(3/2)→~4 I_(11/2)) and 1350 nm(~4 F_(3/2)→~4 I_(13/2)).     

Preparation,characterization of Y~(3+)-doped TiO_2 nanoparticles and their photocatalytic activities for methyl orange degradation

A series of pure and Y3+-doped TiO2 nanoparticles with high photocatalytic activities were prepared by a sol-gel method using tetra-n-butyl titanate as precursor.The as-prepared catalysts were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and diffuse reflectance spectroscopy(DRS).The results indicated that yttrium doping could effectively reduce the crystalline size,inhibit the anatase-to-rutile phase transformation and surppress the recombination of the photogenerated electron-h...     

Impact of grain size,Pr~(3+) concentration and host composition on non-contact temperature sensing abilities of polyphosphate nano- and microcrystals

In this article,varied praseodymium polyphosphate hosts:M~I(Li,Na K)Pr(PO_3)_4 microcrystals and LiLa_(1-x)Pr_x(PO_3)_4(x = 0.01-1)nanocrystals were successfully synthesized by the flux method and the coprecipitation technique,respectively.The size of stoichiometric nanocrystals of LiPr(PO_3)_4 was tuned by the te mpe rature of thermal treatment in range of 35-145 nm.In order to dete rmine the most suitable material for the non-contact optical thermometric applications,the temperature sensing measurements were carried out by using luminescence intensity ratio(LIR)of emission bands corresponding to the ~3 P_1→~3H_5 and ~3P_0→~3 H_5 electronic transitions of Pr~(3+) ions into the 123-423 K temperature range.The influence of the host material composition of M~Ⅰ(Li,Na,K)Pr(PO_3)_4 microcrystals on the sensitivity of luminescent thermometers was studied.It is found that the sensitivity of lithium praseodymium polyphosphate is the highest of all micropowders under investigation.Moreover,it is found that the nanocrystals reveal much higher relative sensitivity in respect to the microcrystalline counterparts.The highest sensitivity of LIR temperature sensing is found for LiPr(PO_3)_4 nanocrystals(35 nm grain size)in the whole temperature range,reaching 0.283%/K at 164 K.The impact of the average grain size on the sensitivity of LIR based thermometers of LiPr(PO_3)_4 nanocrystals was investigated.It is found that the reduction of the grain size from 145 to 35 nm results in the enhancement of the relative sensitivity from0.156 to 0.240%/K at 223 K.Additionally it is found that the high dopant concentration possesses favorable influence on the relative sensitivity of LiLa_(1-x)Pr_x(PO_3)_4 nanocrystalline luminescent thermometers.     

Cerium addition on pitting corrosion of (Cu50Zr50)100-2xCe2x (x=0, 1, 2 and 3) metallic glasses in seawater

The industrial application of metallic glass is a longstanding challenge for researchers in the field. Toward this objective, the electrochemical performance in sea water of Cu-Zr-(Ce) metallic glass with various Ce content was investigated. Cu-Zr-(Ce) metallic glass was fabricated by melt-spinning technique and characterized by X-ray diffraction. The corrosion resistance in seawater was then investigated by potentiodynamic polarization, immersion test, scanning electron microscopy, electron probe microanalysis, and energy dispersive spectrometer analysis. The results showed that Ce addition lowered the corrosion current density of Ce-containing Cu-Zr alloy system. The attack type changed from uniform corrosion of Cu50Zr50 metallic glasses to local one of the Ce-containing alloys. Appropriate content of Ce inhibited the selective dissolution of Cu in the pits and thus improved the corrosion resistance of the alloys.     

Effect of cobalt substitution on structure and magnetic properties of Nd_(0.4)Zr_(0.6)Fe_(10-x)Co_xSi_2(x =0-3) alloys and their ribbons

This study reports the stabilization of the RFe_(12)-type based compounds where part of R and Fe are substituted with Zr and Co and Si, respectively, in order to examine whether these rare-earth-lean materials are suitable for applications as permanent magnets. Structural and magnetic characterization of the family of alloys with the general formula Nd_(0.4) Zr_(0.6) Fe_(10-x)Co_xS_i2(x = 0 -3) and their melt-spun ribbons were carried out using X-ray diffraction and M€ossbauer spectroscopy. The ThMn_(12)-type structure is obtained for all samples as the majority phase with a minority a-Fe(CoSi) phase(less than 5 wt%) as it was estimated by XRD for x = 1 and 2. The Curie temperature increases linearly with Co substitution from 561 K for x = 0 to 712 K for x = 3. The saturation magnetization decreases slightly from 130.5(x =1)to 129.1 A·m~2/kg(x=3), while the anisotropy field is following the same trend.