Urea-assisted Combustion Method Research Articles

Investigation of photoluminescence properties of Eu3+ doped La(OH)3 nanopowder synthesized by combustion method

Pure and different doping percentages of Eu 3+ ion (2, 5, and 10 wt%) doped La(OH)3 nanoparticles were produced using the urea-assisted combustion method followed by a three-hour calcination at 800 °C. A pure hexagonal phase of La(OH)3 structure is confirmed using X-ray diffraction (XRD) results. The photoluminescence (PL) investigations of Eu-doped La(OH)3 nanoparticles revealed orange and red emissions from 5D0→7F1 and 5D0→7F2 transitions of Eu3+ ions with excitation wavelength 395 nm. The CIE coordinate represents the orange and red zone of the La(OH)3 sample doped with Eu3+ions. The CCT values obtained are 2145 K, 2469 K, and 2583 K also the decay lifetime is 0.273 ns, 0.266 ns, and 0.493 ns for 2, 5, and 10 wt% of Eu3+ ions. The results confirmed among the three dopant concentrations of Eu3+ doped La(OH)3 nanoparticles, the optimal concentration of 10 wt% Eu3+ ion can be used for red and orange emitting phosphors.

Urea-assisted combustion synthesis and nearly zero-thermal-quenching luminescence of highly efficient phosphate phosphor

Exploring green-emitting phosphors with high efficiency and thermostability is a significant issue for enhancing lighting and display quality. In this report, we adopted a facile urea-assisted combustion method to rapidly synthesize terbium-activated NaLaP4O12 (NLPO) powder with high crystallinity. The activators Tb3+ are incorporated into the NLPO lattice via equivalently replacing La3+ ions. Excited at 368 nm, it presents a bright green-emitting performance with high internal quantum efficiency, coming from the dominant 5D4→7F5 transitions of Tb3+. The green-emitting content quenching is controlled by the dipole–dipole interaction. Meanwhile, the emission in response to temperature reveals that the nearly zero-thermal-quenching is induced by the high activation energy barrier (0.31 eV) and suitable structure rigidity. Finally, the light emitting diodes are encapsulated using the studied material, manifesting that it would be a prospective green-emitting candidate. The research shows a guide for developing the terbium-activated phosphors with high luminescence efficiency and excellent thermostability.

Influence of the ratio of rare earth oxyorthosilicate R2SiO5 (R = La, Y) hosts on the structure and optical properties of co-doped Pr3+ /Dy3+ phosphors

Praseodymium (Pr3+) and dysprosium (Dy3+) co-doped mixed lanthanum/yttrium oxyorthosilicates (La2-xYxSiO5, x = 0.5, 1 and 2) phosphors were synthesized using urea-assisted combustion method. The X-ray diffraction (XRD) patterns showed the pure monoclinic phases of La2SiO5 (x = 0) and Y2SiO5 (x = 2) and mixed phases of La2-xYxSiO5. The diffuse reflectance spectra of the phosphors showed a broad absorption peak with a maximum around 376 nm assigned to O2−→ Pr4+ charge transfer band. The band gaps of the Pr3+/Dy3+ co-doped La2-xYxSiO5 increased from 2.7 to 5.1 eV as the value of x increased from 0 to 2. The luminescent properties were measured when the samples were excited using three different sources, namely 450 W Xenon lamp, 325 He-Cd laser and electron beam. The photoluminescence (PL) emission spectra recorded using monochromatized Xenon lamp showed tunable emission for different excitation wavelengths. For example, when the PL spectra were recorded under 294 nm excitation, using Xenon lamp, emissions from self-trapped excitons (STE) in SiO2, f→f transitions of Dy3+ and Pr3+ were observed. The emission monitored under 349 nm excitation showed the STE peak and the four emission lines of Dy3+. However, when the phosphors were excited using a 325 nm He-Cd laser, the STE emission and four Dy3+ lines were observed in all the samples, but the four manifolds emission from the 1D2→3H4 transition of Pr3+ were only observed for x = 1.5 and 2. Furthermore, the cathodoluminescence (CL) spectra showed the STE band, four emission lines of Dy3+ and four manifolds emission from the 1D2→3H4 transition of Pr3+. The tunable colours of the phosphors were shown in International Commission on Illumination (CIE) coordinate diagram.

Near ultraviolet excited down conversion Eu and Er co-doped CaAl2O4 color tunable nano-phosphors: Structural, morphological and photolumniscent characteristics

Abstract A series of CaAl2O4:Eu3+ (1 mol%) co-doped with Er3+ (0, 1, 2, and 5 mol%) was synthesized by urea assisted combustion method at 600 °C and further calcinations was done at 1000 °C to enhance the crystalline character and luminescence properties. Synthesized samples were characterized structurally and optically using the X-ray diffraction (XRD) and spectrofluorometer respectively. From XRD analysis, monoclinic phase of CaAl2O4 is reported in all the samples indicating that doping of Eu3+ and Er3+ do not change the crystalline structure of calcium aluminate. Both Eu3+ and Eu2+ states were detected in the synthesized materials whose ratio changes with calcination as well as with co-doping of the Er3+ ions. CaAl2O4:Eu3+ (1 mol%) synthesized at 600 °C show high intense peak around 440 nm due to presence of Eu2+ state, whose intensity decrease with co-doping and upon calcination where as at the same time intensity of peak in the red region due to the presence of Eu3+ increases. In the compounds calcined at 1000 °C, electric dipole 5D0 → 7F3 transition of Eu3+ at 657 nm appears as peak with highest intensity. The Er3+ ion acts as sensitizer and enhances the luminescent properties of co-doped samples.

Energy transfer from Ce3+to Dy3+ ions for white light emission in Sr2MgAl22O36:Ce3+, Dy3+ phosphor

Series of Sr2MgAl22O36:Ce3+, Sr2MgAl22O36:Dy3+ and Sr2MgAl22O36:Ce3+,Dy3+ phosphors were synthesized by urea-assisted combustion method. The identification of phase and morphology of the prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Photoluminescence excitation (PLE) and emission spectra of the as-prepared samples were investigated. Photoluminescence studies revealed that the luminescence intensity of Ce3+ ion increases with increasing concentration in Sr2MgAl22O36:Ce3+ and no concentration quenching have been witnessed. Similar trend was observed for Sr2MgAl22O36:Dy3+ with increasing Dy3+ concentration. The energy transfer from Ce3+ to Dy3+ in Sr2MgAl22O36 host has been achieved successfully to produce white light emission. The calculated Commission Internationale de L′Eclairage (CIE) chromaticity coordinates for the Sr2MgAl22O36:Ce3+, Dy3+ phosphor are (x = 0.302, y = 0.357). The values of CIE chromaticity coordinates and correlated color temperature (CCT) of 6798 K endorse Sr2MgAl22O36:Ce3+, Dy3+ phosphor as potential candidate for cool white-light emission.

An Investigation of Facile One-Pot Synthesis of Li2FeSiO4/C Composite for Li Ion Batteries

Li2FeSiO4 and its carbon composite are prepared by an urea-assisted combustion method. The synthesis has been carried out in different urea concentrations, namely 1 Molar (M), 2 M and 3 M urea in the cost-effective ambient atmospheric condition. The x-ray diffraction analysis confirms the orthorhombic structure of Li2FeSiO4 compounds. The urea-assisted combustion reaction enhanced the phase purity of the compound and prevented the oxidation of ferrous ions in Li2FeSiO4. The x-ray photo electron spectroscopy analysis further confirmed the reduction of Fe3+ concentration in Li2FeSiO4 while adding urea. The Li2FeSiO4 compound formation in the presence of urea occurred at a temperature < 623 K. The one-pot synthesis of Li2FeSiO4/C with the help of starch and urea in ambient atmospheric condition resulted in Li2FeSiO4 with an orthorhombic crystal structure. The carbon coating in an amorphous nature is observed and the lattice dimension values of Li2FeSiO4/C are 6.248 A, 5.330 A, and 5.029 A. The lattice parameter has remained unchanged with carbon addition. The addition of 5% carbon to Li2FeSiO4 improves the electrical conductivity and lithium diffusion coefficient to 7.24 × 10−4 S cm−1 and 5.54 × 10−6 cm2, respectively. The coulombic efficiency and capacity retention after 50 cycles of Li2FeSiO4/C composite are around 83% and 95%, respectively.

White light emission through efficient energy transfer from Ce3+ to Dy3+ ions in Ca3Mg3(PO4)4 matrix aided by Li+ charge compensator

In this work, we have comprehensively explored the energy transfer process between Ce3+ and Dy3+ ions doped in Ca3Mg3(PO4)4 host lattice. The phosphors were synthesized by facile urea-assisted combustion method. The charge imbalance, produced due to doping of trivalent lanthanides in the divalent sites of the host lattice, has been compensated by adding Li+ charge compensator. The structural characterization by Rietveld refinement, morphological and FTIR studies were performed on the as-prepared Ca2.96Mg3(PO4)4:0.01Ce3+, 0.01Dy3+, 0.02Li+ phosphor. The diffuse reflectance spectra and the photoluminescence spectra of the prepared phosphors and the electron-vibration interaction (EVI) parameters of Ca3Mg3(PO4)4:Ce3+,Li+ phosphor were thoroughly analysed. Ca3Mg3(PO4)4:Ce3+,Dy3+,Li+ phosphor exhibited its ability to produce white light emission at UV excitation wavelength 316nm. The codoping of Ce3+ ions enhanced the PL emission intensity of Dy3+ by ten times as compared to the intensity obtained for the samples that were singly-doped with Dy3+. The results suggest the use of single-phased Ca2.96Mg3(PO4)4:0.01Ce3+, 0.01Dy3+, 0.02Li+ phosphor as potential white light emitting phosphor.

The dynamics of the photoluminescence of Pr3+ in mixed lanthanum yttrium oxyorthosilicate hosts

Praseodymium (Pr3+) doped mixed lanthanum yttrium oxyorthosilicate (LaYSiO5) powder phosphors were synthesized using urea-assisted combustion method. The molar ratio of La:Y were varied in the following manner: La2-xYxSiO5 (x=0, 0.5, 1, 1.5, 2), were x=0 is pure La2SiO5, x=2 is pure Y2SiO5 and x=0.5, 1, and 1.5 are the admixtures of the two compounds. The X-ray diffractometer results showed that the La2SiO5 and Y2SiO5 crystalized in their pure monoclinic phases, while their admixtures are both present in the same phase. The Burstein–Moss (BM) shift was used to explain the increase observed in the band gap after doping. The influence of the host crystal field on the branching ratios of the photoluminescence emission intensities of the 3P0 and 1D2 energy levels of Pr3+ were studied. The electronic transition from the 3P0 transition dominated the emission spectra when x=0, while the 1D2 electronic transition dominated when x=2. The variation in the branching ratios of the 3P0 and 1D2 emission with the change in the molar ratio of La:Y could be due to 3P0→1D2 non-radiative transitions, which increased with the crystal field of the host as the value of x increased (i.e., as the molar ratio of Y increases). Furthermore, it was shown that the 3P0 emission lines emerged from Pr3+ ions occupying La1 and Y1 sites of La2SiO5 and Y2SiO5 respectively, while the 1D2 emission lines emerged from Pr3+ ions occupying La2 and Y2 sites. The decay curve showed three lifetime components from both 3P0 and 1D2 emission lines, with the 1D2 lines having higher lifetimes in all cases.

Optical properties and chemical composition analyses of mixed rare earth oxyorthosilicate (R2SiO5, R=La, Gd and Y) doped Dy3+ phosphors prepared by urea-assisted solution combustion method

Dysprosium (Dy3+) doped lanthanum gadolinium oxyorthosilicate (LaGdSiO5), lanthanum yttrium oxyorthosilicate (LaYSiO5) and gadolinium yttrium oxyorthosilicate (GdYSiO5) phosphors (in powder form) were synthesized by urea-assisted combustion method. The X-ray diffractometer analysis confirmed that the LaGdSiO5, LaYSiO5 and GdYSiO5 crystalized in monoclinic phases. The chemical composition of the phosphors was analyzed by measuring the atomic and molecular ionic species using the time of flight secondary ion mass spectroscopy (ToF SIMS). In addition, ToF SIMS imaging technique was used to determine the distribution of the Dy3+ dopant ions on the surface on the phosphors. The average crystallite sizes and lattice strains of the phosphor were increased by Dy3+ doping. The field emission scanning electron microscope images showed that the powders were made up of an agglomeration of particles with no regular shape. The photoluminescence data showed narrow line emission peaks at the wavelengths of 485nm (minor emission) and 573nm (major emission) associated with the f→f transitions of Dy3+. The photoluminescence (PL) measurements showed that the emission peak of LaGdSiO5:Dy3+ was ~3× more intense than those of LaYSiO5:Dy3+ and GdYSiO5:Dy3+ when excited using monochromatic xenon lamp with a wavelength of 241nm. However, when the powders were excited using a 325nm He–Cd laser, the highest PL emission intensity was observed from GdYSiO5:Dy3+.

Luminescence properties and determination of optimal RE3+(Sm3+, Tb3+and Dy3+) doping levels in the KYP2O7host lattice obtained by combustion synthesis

The β-KYP2O7 powders doped with Sm3+, Tb3+ and Dy3+ were obtained using a one-step urea-assisted combustion method. Their structural properties were characterized by X-ray diffraction (XRD) whereas spectroscopic properties like excitation, emission and luminescence kinetics were investigated at room temperature. β-KYP2O7 doped with Sm3+ and Dy3+ showed concentration quenching above 2 mol% of dopants whereas Tb3+ containing materials could be doped with higher concentrations. The main mechanisms of concentration quenching were identified as dipole–dipole for Sm3+ and Dy3+. Both dopants due to the abundant energy levels are strongly prone to quenching due to the non-radiative CR process whose efficiency strongly increases with the concentration of optically active ions. In the case of Tb3+ emission from both 5D3 and 5D4 levels was recorded. The 5D3 level vastly depopulates due to the CR process upon increase of the Tb3+ content whereas the slight 5D4 emission remains stable up to 5 mol%.

One step urea assisted synthesis of polycrystalline Eu3+ doped KYP2O7 – luminescence and emission thermal quenching properties

KYP2O7 powders doped with Eu3+ were obtained for the first time by a one-step urea-assisted combustion method. Detailed structural properties were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and X-ray fluorescence (EDX). Spectroscopic properties like excitation, emission and luminescence kinetics were investigated in the temperature range of 30–550 °C. The KYP2O7 doped with Eu3+ phosphor has a broad and intense absorption band centered at 213 nm, an absolute quantum yield of up to 62% and a luminescence quenching temperature of T0.5 = 400 °C. The thermal behavior analysis of the luminescence shows that non-radiative internal losses are the main mechanism responsible for quenching of the luminescence.

Tunable and white photoluminescence from Tb3+–Eu3+ activated Ca0.3Sr0.7Al2O4 phosphors and analysis of chemical states by X-ray photoelectron spectroscopy

Tb3+ and Eu3+ activated Ca0.3Sr0.7Al2O4 phosphors with tunable emissions were synthesized via urea assisted combustion method. The phosphors were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and photoluminescence (PL) spectroscopy. The XRD pattern of the Ca0.3Sr0.7Al2O4:Tb3+, Eu3+ powder showed was composed of a single phase associated with monoclinic SrAl2O4, suggesting that SrAl2O4 was the main structure in the Ca0.3Sr0.7Al2O4 mixed aluminate host and Ca2+ substituted the Sr2+ ions. Consistent with the three dimensional structure of SrAl2O4, the XPS data indicated that there were two different lattice sites occupied by Sr2+ in the lattice and resultantly Ca2+ could also be found at two different lattice sites. Tunable and white PL was generated when the phosphors were optically excited at different wavelengths using a monochromatized xenon lamp. The white PL with the Commission International de L’Eclairage (CIE) coordinates (x=0.343, y=0.325) was a result of the combination of the red line emission from Eu3+ and the blue and green line emissions from Tb3+.

Synthesis and pseudocapacitive investigation of LiCr x Mn2-x O4 cathode material for aqueous hybrid supercapacitor

A series of Cr-substituted LiMn2O4 samples (LiCr x Mn2-x O4, 0 ≤ x ≤ 0.3) were synthesized by a urea-assisted combustion method to enhance pseudocapacitive properties of LiMn2O4 material in aqueous electrolyte. Their structure and morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The LiCr x Mn2-x O4 and activated carbon (AC) electrode were used as the cathode and anode in hybrid supercapacitors, respectively, which capacitive properties were determined by cyclic voltammetry (CV), galvanostatic charge/discharge test, and electrochemical impedance spectroscopy (EIS) in Li2SO4 solution. The results revealed that the partial substitution of Mn3+ by Cr3+ decreased initial capacity, but it prevented capacity fading. In the working voltage of 0–1.4 V, the AC/LiCr0.1Mn1.9O4 capacitor delivered an initial specific capacitance of 41.6 F g−1 (based on the total active mass of two electrodes) at a current density of 100 mA g−1 in 1 M Li2SO4 solution. After 1,000 cycles, its capacity loss was only 1.7 %.

Identification of Eu oxidation states in a doped Sr5(PO4)3F phosphor by TOF-SIMS imaging

An Eu-doped Sr5(PO4)3F phosphor with a hexagonal apatite structure was prepared by a urea assisted combustion method. There was evidence of the reduction of Eu3+ to Eu2+ based upon the photoluminescence data. This was confirmed with X-ray photoelectron spectroscopy. Normally, it is very difficult to distinguish between two oxidation states with time-of-flight secondary ion mass spectrometry (TOF-SIMS), but it is shown that the parallel detection capability of the technique allows full molecular and isotopic characterization of the matrix chemistry. The two states were detected by the EuF+ and EuF2+ species, ostensibly the Eu(II) and Eu(III) oxidation states, respectively.

Electrochemical Lithium Insertion Behavior of Combustion Synthesized V2O5 Cathodes for Lithium-Ion Batteries

Sub-micron size vanadium pentoxide (V2O5) particles are synthesized by novel urea assisted combustion method. Comprehensive characterization and electrochemical studies related to sintering temperature and duration are presented. X-ray diffraction (XRD) patterns showed the formation of pure-phase V2O5 and the surface morphologies are studied by field emission scanning electron microscopy (FE-SEM). Electrochemical properties of the sintered V2O5 as a cathode in lithium-ion batteries are explored with respect to synthesis parameters using cyclic voltammetry and galvanostatic charge-discharge studies. The V2O5 particles obtained from 600°C sintering temperature for 1 h exhibits a higher initial discharge capacity ∼320 mAh g−1 (∼2.2 Li per V2O5) between 1.75–4.0 V vs. Li/Li+ at 0.1 C rate and shows good capacity retention of >70% after 50 cycles. Electrochemical impedance spectroscopy (EIS) studies show that the urea combustion method enables increased Li+ ion diffusion pathways and electro-active surface area in V2O5 particles. Ball milling procedure with or without carbon is also adopted to further reduce the particle size of V2O5 and related electrochemical properties are evaluated and described.

Luminescence response and CL degradation of combustion synthesized spherical SiO 2:Ce nanophosphor

This study was aimed to systematically investigate the luminescence response of SiO 2:Ce 3+ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO 2:Ce 1m% samples were also annealed at 1000 °C for 1 h in a charcoal environment to reduce incidental Ce 4+ to partial Ce 3+ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3–8 nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO 2 was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO 2:Ce 3+ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO 2:Ce 3+ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO 2:Ce 3+ annealed at 1000 °C were obtained.