The effect of different gas atmospheres on luminescent properties of pulsed laser ablated SrAl2O4:Eu,Dy thinfilms

SrAl₂O₄:Eu²⁺,Dy³⁺ thin films were grown on Si (1 0 0) substrates using the pulsed laser deposition (PLD) technique to investigate the effect of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological, photoluminescence (PL) and cathodoluminescence (CL) properties of the films. The films were ablated using a 248 nm KrF excimer laser. Atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and fluorescence spectrophotometry were used to characterize the thin films. Auger electron spectroscopy (AES) combined with CL spectroscopy were employed for the surface characterization and electron-beam induced degradation of the films. Better PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres with respect to those prepared in vacuum. A stable green emission peak at 515 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions were obtained with less intense peaks at 619 nm, which were attributed to transitions in Eu³⁺. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The CL intensity increased under prolonged electron bombardment during the removal of C due to electron stimulated surface chemical reactions (ESSCRs) on the surface of the SrAl₂O₄:Eu²⁺, Dy³⁺ thin films. The CL stabilized and stayed constant thereafter.     

Synthesis, characterization and optical properties of water-soluble ZnS:Mn nanoparticles

ZnS nanoparticles with Mn²⁺ doping (0.5-20%) have been prepared through a simple chemical method, namely the chemical precipitation method. The structure of the nanoparticles has been analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV-vis spectrometer. The size of the particles is found to be 3-5 nm range. Photoluminescence spectra were recorded for undoped ZnS nanoparticles using an excitation wavelength of 320 nm, exhibiting an emission peak centered at around 445 nm. However, from the Mn²⁺-doped samples, a yellow-orange emission from the Mn²⁺⁴T₁-⁶A₁ transition is observed along with the blue emission. The prepared Mn²⁺-doped sample shows efficient emission of yellow-orange light with the peak emission 580 nm with the blue emission suppressed. The maximum PL intensity is observed only at the excitation energy of 3.88 eV (320 nm). Increase in stabilizing time up to 48 h in de-ionized water yields the enhancement of emission intensity of doped (4% Mn²⁺) ZnS. The correlation made through the concentration of Mn²⁺ versus PL intensity resulted in opposite trend (mirror image) of blue and yellow emissions.     

PL and CL degradation and characteristics of SrAl2O4: Eu,Dy phosphors

Strontium aluminate phosphors are ideal for luminescent infrastructure materials. Their brightness and persistent glow time are much higher than previously used sulphide phosphors. Strontium aluminates prepared by the sol–gel and combustion methods are compared with commercially available strontium aluminate. High luminescent efficient SrAl₂O₄:Eu²⁺,Dy³⁺ pulsed laser deposited (PLD) thin films were also produced using the commercially available powder. Photoluminescence (PL) degradation studies showed that the phosphor intensity decreased about 20% over a period of 2 weeks under ultraviolet (UV) irradiation. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) showed that cathodoluminescence (CL) degradation is due to the formation of SrO due to electron stimulated surface reactions. The light output mechanism of the phosphor is also discussed in more detail.     

Infrared-to-visible upconversion in Er and Er/Yb activated Sb2O4 nanopowders prepared by sol-gel route

We prepared Er³⁺ doped and Er³⁺/Yb³⁺ codoped Sb₂O₄ nanocrystals by the sol-gel method. The Raman, X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra of the samples were studied. The phonon energy of the Sb₂O₄ nanocrystals is very low (the maximum value being 461 cm⁻¹). The upconversion (UC) red emission of the Er³⁺/Yb³⁺ codoped sample is very strong at 975 nm laser diode excitation. The Sb₂O₄ nanocrystals will be a promising luminous material.     

Synthesis and characterization of Cu doped ZnS nanoparticles using TOPO and SHMP as capping agents

Undoped and Cu²⁺ doped (0.2-0.8%) ZnS nanoparticles have been synthesized through chemical precipitation method. Tri-n-octylphosphine oxide (TOPO) and sodium hexametaphosphate (SHMP) were used as capping agents. The synthesized nanoparticles have been analyzed using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectrometer (FT-IR), UV-vis spectrometer, photoluminescence (PL) and thermo gravimetric-differential scanning calorimetry (TG-DTA) analysis. The size of the particles is found to be 4-6 nm range. Photoluminescence spectra were recorded for ZnS:Cu²⁺ under the excitation wavelength of 320 nm. The prepared Cu²⁺-doped sample shows efficient PL emission in 470-525 nm region. The capped ZnS:Cu emission intensity is enhanced than the uncapped particles. The doping ions were identified by electron spin resonance (ESR) spectrometer. The phase changes were observed in different temperatures.     

Characterization and Photocatalytic Performance of Rb+-Doped TiO2 Photocatalysts

ABSTRACT

Rb⁺-doped TiO₂ nanoparticles with higher photocatalytic activity were prepared by sol–gel method. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX), and surface area (BET) measurements. The photocatalytic activity for the degradation of rhodamine B (RhB) was evaluated. The effects of calcination temperature, Rb⁺-doping amount, and the dosage of catalyst in the reaction liquid were investigated. The results showed that Rb⁺ doping can inhibit phase transformation from anatase to rutile, increase surface area of TiO₂ crystals, and reduce crystallite size. TiO₂ doped with 1% Rb⁺ and calcined at 650°C shows much higher photoactivity than the others when the doping level of Rb⁺ and calcination temperature are 0–5% and 350–850°C, respectively. The kinetics of the degradation of RhB was also analyzed. The kinetics of this reaction fits the pseudo first-order kinetics model well, and the reaction rate constants for pure TiO₂ and Rb1-650 are 0.086 min^?1 and 0.226 min^?1 respectively. Doping with Rb⁺ improves the photocatalytic activity of TiO₂ significantly.     

Concentration effect of Tm on cathodoluminescence properties of SiO2:Tm and SiO2:Ho,Tm systems

Cathodoluminescence (CL) properties of SiO₂ powders activated with thulium (Tm³⁺) and holmium (Ho³⁺) ions prepared by a sol–gel process were investigated. Different molar concentrations of Tm³⁺ co-doped with Ho³⁺ were studied. The 460 nm peak was monitored and the influence of the beam energy and concentration of Tm³⁺ ions on the emission properties of this peak was also monitored. The peculiar behavior whereby the 460 nm emission peak decreases and the increase in the 705 and 865 nm peaks with the increase in the concentration of Tm³⁺ ions is reported. The relationship between the accelerating beam voltage and the CL intensity of the blue emission peak (460 nm peak) is established. Morphology, particle size and optical properties were characterized with Scanning electron microscopy (SEM), UV/VIS Lambda 750 S spectrometer and Auger electron spectroscopy (AES) equipped with Ocean Optics S2000, respectively.     

Synthesis and luminescent properties of nanoparticles GdCaAl3O7:RE (RE=Eu, Tb) via the sol-gel method

By using metal nitrates as starting materials and citric acid as complexing agent, GdCaAl₃O₇:Eu³⁺ and GdCaAl₃O₇:Tb³⁺ powder phosphors were prepared by a citrate-gel method. Thermal analysis (TG-DTG), X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results of the XRD indicated the precursor samples began to crystallize at 800 °C and the crystallinity increased with elevation the annealing temperature. TEM images showed that the phosphor particles were basically of spherical shape, with good dispersion about a particle size of around 40-70 nm. Upon excitation with UV irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole ⁵D₀-⁷F₂ transition of Eu³⁺, and at around 543 nm corresponding to the ⁵D₄-⁷F₅ transition of Tb³⁺. The dependence of photoluminescence intensity on Eu³⁺ (or Tb³⁺) concentration and annealing temperature were also studied in detail.     

I. Spectroscopic Investigation of Charge Transrer Complexes of Oxime Intermediates Prepared from Some Pharmaceutical Carbonyl Compounds

Spectroscopic studies on the reaction of iodine as π-acceptor and chloronil as π-acceptor with oxime intermediates prepared from certain pharmaceutical carbonyl compounds are reported. These compounds include Δ^1,4 -3-corticosteroids (prednisone, prednisolone, dexamethasone), Δ⁴-3-ketosteroids (progesterone, testosterone propinate, nandrolone phenpropionate), griseofulvin, carvone, and menthone. The spectroscopic techniques applied are IR, far IR spectroscopy, H¹, C¹³NMR, mass spectra (MS), fast atom bombardment mass spectra (FABMS), electron spin resonance (ESR) and microanalysis of the reaction products. The structure elucidation studies of these complexes confirmed the charge transfer complex (CTC) formation.     

Characterization and photocatalytic activity of Zn–TiO2/AC composite photocatalyst

Activated carbon (AC) supported Zn²⁺–TiO₂ photocatalyst was prepared by sol–gel method. The prepared samples were characterized by X-ray diffraction, scanning electron micrograph, nitrogen absorption, diffuse reflectance UV/VIS and X-ray photoelectron spectroscopy. Using toluene as a pollution target, the photocatalytic activity of photocatalyst was evaluated. The results showed that prepared photocatalyst was obviously helpful for the removal of toluene in air. The photocatalytic degradation of toluene by Zn²⁺–TiO₂/AC reached 100% for 40 min and remained 75% after 160 min, while degradation by TiO₂ was only 30%. It indicated that the photocatalytic activity of prepared photocatalyst was enhanced. It is due to Zn²⁺-doping increased the oxidation and reduction of hole–electron pairs, which was the important factor in heterogeneous photocatalysis.     

Enhanced blue emission and EPR study of LaMgAl11O19:Eu phosphors

Europium doped LaMgAl₁₁O₁₉ phosphor was prepared by the combustion method. The as-prepared and post-treated (1350 °C 10 h 5% H₂+95% N₂) phosphors were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques. XRD patterns show that LaMgAl₁₁O₁₉:Eu phosphors have hexagonal structure. FT-IR spectrum exhibits absorption bands corresponding to the stretching vibration of AlO₄ and AlO₆. Morphological studies reveal that this phosphor has faceted plates of varying sizes and shapes. The as-prepared LaMgAl₁₁O₁₉:Eu phosphor consists of both Eu³⁺ and Eu²⁺ ions. The phosphor exhibits a bright blue emission at 450 nm (4f⁶5d→4f⁷ transition of Eu²⁺). On post-treating the phosphor we are able to enhance the blue emission efficiency by 330%. The process was detected from the evolution of excitation, emission and EPR spectra and the results are discussed.     

Enhanced photocatalytic activity and stability of nano-scaled TiO2 co-doped with N and Fe

Titanium dioxide (TiO₂) nanoparticles co-doped with N and Fe were prepared via modified sol-gel process. The products were characterized by transmission electron microscopy (TEM), N₂ adsorption, X-ray diffraction (XRD), Raman spectroscopy, UV-vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). It is shown that the prepared TiO₂ particles were less than 10 nm with narrow particle size distribution. The addition of MCM-41 caused the formation of Ti-O-Si bond which fixed the TiO₂ on MCM-41 surface, thus restricted the agglomeration and growth of TiO₂ particles. The photocatalytic performance in the degradation of methylene blue showed that N, Fe co-doped TiO₂ exhibited much higher photocatalytic activity than doped sample with nitrogen or Fe³⁺ alone under both UV and visible light. N, Fe co-doping decreased the loss of doping N during the degradation reaction, thus increased the photocatalytic stability. It was also found that the nitridation time had significant influence on the photocatalytic activity of prepared TiO₂ catalysts.     

Synthesis and characterization of core-shell structured SiO2@YVO4:Yb,Er microspheres

In this paper, the core-shell structured SiO₂@YVO₄:Yb³⁺,Er³⁺ microspheres have been successfully prepared via a facile sol-gel process followed by a heat treatment. X-ray diffraction, field emission scanning electron microscopy, energy disperse X-ray spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and photoluminescence spectra were used to characterize the samples. The results reveal that the SiO₂ spheres have been successfully coated by YVO₄:Yb³⁺,Er³⁺ phosphors to form core-shell structures and the size of obtained microspheres has a uniform distribution. Additionally, the samples exhibit bright green luminescence under the excitation of a 980 nm laser diode. The photoluminescence intensity increases with the number of coatings. These core-shell structured SiO₂@YVO₄:Yb³⁺,Er³⁺ microspheres may have great potential in the fields of infrared detection and display devices.     

Thermoluminescent and stuctural properties of BaAl2O4:Eu,Nd,Gdphosphors prepared by combustion method

BaAl₂O₄:Eu²⁺,Nd³⁺,Gd³⁺ phosphors were prepared by a combustion method at different initiating temperatures (400–1200 °C), using urea as a comburent. The powders were annealed at different temperatures in the range of 400–1100 °C for 3 h. X-ray diffraction data show that the crystallinity of the BaAl₂O₄ structure greatly improved with increasing annealing temperature. Blue-green photoluminescence, with persistent/long afterglow, was observed at 498 nm. This emission was attributed to the 4f⁶5d¹–4f⁷ transitions of Eu²⁺ ions. The phosphorescence decay curves were obtained by irradiating the samples with a 365 nm UV light. The glow curves of the as-prepared and the annealed samples were investigated in this study. The thermoluminescent (TL) glow peaks of the samples prepared at 600 °C and 1200 °C were both stable at ∼72 °C suggesting that the traps responsible for the bands were fixed at this position irrespective of annealing temperature. These bands are at a similar position, which suggests that the traps responsible for these bands are similar. The rate of decay of the sample annealed at 600 °C was faster than that of the sample prepared at 1200 °C.     

Spherical Zn2SiO4:Eu@SiO2 phosphor particles in core-shell structure: Synthesis and characterization

Spherical SiO₂ particles have been coated with Zn₂SiO₄:Eu³⁺ phosphor layers by a Pechini sol-gel process. The microstructure and luminescent properties of the obtained Zn₂SiO₄:Eu³⁺@SiO₂ particles were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and lifetime. The results demonstrate that the Zn₂SiO₄:Eu³⁺@SiO₂ particles, which have regular and uniform spherical morphology, emitted an intensive red light emission at 613 nm under excitation at 395 nm. Besides, the effects of the Eu³⁺ concentration, annealing temperature and charge compensators of Li⁺ ions on the PL emission intensities were investigated in detail.     

Characterization, EPR and luminescence studies of ZnAl2O4:Mn phosphors

ZnAl₂O₄:Mn green light emitting powder phosphors have been prepared by urea combustion technique involving furnace temperatures about 500 °C in a short time (<5 min). The prepared powders were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectrometry and the surface area measurements by a Brunauer-Emmet-Teller (BET) adsorption isotherms. The EPR spectrum exhibits a resonance signal at g≈2.0, which shows a six-line hyperfine structure (hfs). From the EPR spectra the spin-Hamiltonian parameters have been evaluated at room temperature as well as at 110 K. EPR and photoluminescence (PL) studies revealed that manganese ions were present in divalent state and the site symmetry around Mn²⁺ ions is distorted tetrahedral. The spin concentration (N), the paramagnetic susceptibility (χ) and the zero-field splitting parameter (D) have been evaluated and discussed. The green emission at 511 nm in ZnAl₂O₄:Mn phosphor is assigned to a transition from the upper ⁴T₁→⁶A₁ ground state of Mn²⁺ ions.     

溅射制备纳米晶GaN∶Er薄膜的室温发光特性

利用直流磁控共溅射方法制备了GaN:Er薄膜.X射线衍射结果显示薄膜为纳米多晶结构,根据谢乐公式,计算得到了GaN薄膜晶粒的平均大小为58nm;透射电子显微镜结果显示为非晶基质中镶嵌了GaN纳米颗粒,尺寸在6—8nm之间;紫外可见谱结果表明在500—700nm的可见光范围内,薄膜的平均透过率大于80%,在紫外可见谱基础上,利用Tauc公式计算得到了纳米晶GaN薄膜的光学带隙为322eV;最后,测量了GaN:Er薄膜的室温光致发光谱,获得了Er³⁺离子在554nm处的强烈绿光发射. 关键词： 纳米晶GaN薄膜 3+掺杂')" href="#">Er³⁺掺杂 光学带隙 光致发光     

Preparation and photoluminescent properties of Ni-doped ZrO2 fibers

Ni²⁺-doped ZrO₂ precursor fibers were prepared via sol-gel technique by dry-spinning method and then heat-treated at different temperatures. The surface of the fibers is smooth with uniform diameter and no cracks have been observed by scanning electron microscopy (SEM). The emission intensity reaches a maximum value at 1 mol% Ni²⁺ because of the concentration quenching. The photoluminescence (PL) relative intensity is apparently intensifying with increasing temperature before 700 °C due to the crystallinity of the ZrO₂ lattice improvement. The PL results show that the typical emission center is at 510 nm excited at 315 nm.     

Hydrothermal synthesis and optical characteristics of Eu in Zn2SnO4 nanocrystals

Zn₂SnO₄:Eu³⁺ nanocrystals were one-step synthesized by hydrothermal method for the first time. All the products were systematically characterized by powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), electron probe X-ray microanalyzer (EPMA), photoluminescence (PL) and photoluminescent excitation (PLE). The characteristic peak of Eu³⁺-doped in Zn₂SnO₄ nanocrystals was also detected. The luminescent properties of blank and Eu³⁺-doped Zn₂SnO₄ nanocrystals were reported.     

The effect of Mg ions on the photoluminescence of Ce-doped silica

In this paper, we report enhanced luminescence of Mg-co-doped silica gels, which were prepared by a sol-gel method. The total amount of Ce³⁺ ions was kept constant in this experiment at 0.5 mol% total doping. Structural, morphological, thermal, optical absorption and photoluminescence studies were employed. The XRD spectra show that all the samples are non-crystalline. Scanning electron microscopy (SEM) images show that the particles were in nano-range and spherical in shape. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) of samples depict that the presence of dopant and co-dopant decreases the endothermic peak temperature; while Ce³⁺ increase the yield, Mg²⁺ reduces it. UV analyses revealed that the presence of Ce³⁺ ions increases transmittance but lowers absorbance of annealed silica xerogels, while that of Mg²⁺ ions reduces transmittance but increases absorbance. Luminescence intensities were compared for different gels with and without Mg particles by varying the different concentrations of Mg. Silica containing Mg²⁺ ions had broad blue emission due to energy transfer from Mg²⁺ to Ce³⁺, which is due to radiative recombination. An increase in luminescence intensity was observed as the Mg²⁺ to Ce³⁺ ratio increased for the range investigated.