Urea Combustion Route Research Articles

Probing into multifunctional deep orange-red emitting Sm3+-activated zincate based nanomaterials for wLED applications

Empirical-investigations on deep-orange-red emitting BaLa2ZnO5:Sm3+ phosphor-powders generated via low-temperature and environmentally-sound urea-combustion route, are presented. In-depth crystallographic-analysis, conducted via XRPD-facilitated-Rietveld-refinement, reveals their tetragonal-crystallinity. Emission-spectra under 413 nm-energization, yields an intense-band at 708 nm, thus imparting deep orange-red color to powders. The best luminous-performance has been marked at × = 0.02 Sm3+content. Also, various radiative-possessions including decay-time, intrinsic life-time, quantum-efficiency and relaxation-rate, which reflect their better luminance-potentiality, have been evaluated. Color-coordinates have realized their deep-orange radiance, which are proximate to those of AMBER LED-NSPAR 70-BS. All-in-all, present work successfully marked their utilization in high-performance warm-wLEDs, signage, bio-imaging, solar-cells and lasing applications.

Crystal structure engineering and optical analysis of novel greenish Sr9Al6O18:Er3+ nanomaterials for NUV excitable cool-white LED applications

Novel green emanating Sr9-xAl6O18:xEr3+ (x = 0.001–0.04) nanomaterials, were developed via a reliable, economical and low temperature urea combustion route. Photoluminescence spectra reported that these could be energized effectively via 379 nm near UV light and then displayed a green peak in the visible domain (560 nm). Improved CIE parameters like color coordinates (0.2862, 0.5437), 83.82% color purity and 6452 K CCT (correlated color temperature), thus promised their magnified performance for various photonic applications like cool-white LEDs, solar cells, bio-imaging probes, optical sensors and lasers. Also, the obtained results of this paper can be resorted to design new Sr9Al6O18-based materials.

On the infrared emissions of Er3+/Yb3+ co-doped SrAl2O4

Infrared emitting SrAl2O4:Er3+ and SrAl2O4:Er3+,Yb3+ powder samples were prepared by the urea combustion route. Powder X-ray diffraction technique was used to find the phase formation. Upon excitation at 980nm, broad infrared emission of Er3+ ions at around 1.54μm was observed. The dependency of infrared luminescence intensity with co-doping was discussed.

Luminescence behaviors and infrared-to-visible energy conversion in Er3+/Yb3+ -doped CaZr4O9 phosphors

Phosphor powders of CaZr4O9:Er3+ and CaZr4O9:Er3+,Yb3+ were prepared by the urea combustion route. The crystal structure was characterized by powder XRD measurement. The optical properties were studied using absorption and photoluminescence (PL) spectroscopy. Upon excitation at 978 nm, the upconversion (UC) luminescence properties of Er3+ and Er3+,Yb3+ co-doped CaZr4O9 phosphors were analyzed. Energy transfer mechanism was discussed to understand the UC luminescence process for the Er3+ and Er3+,Yb3+ co-doped CaZr4O9 phosphors. From the pump power dependent green and red luminescence intensity analysis, required number of photons to populate the excited emitting levels are estimated and observed that the green emission intensity exhibits faster increase rates than red emission as a function of pump power. Upon excitation at 978 nm, the UC mechanism was discussed in terms of the experimental results.

Photoluminescence and ESR identification of γ-ray irradiation induced defects responsible for thermoluminescence in Tb3+ activated hibonite (CaAl12O19) powder material

CaAl12O19 powder activated with Tb ions has been prepared by the urea combustion route. Phase evolution of the powder is determined by X-ray diffraction techniques. Photoluminescence emission of CaAl12O19:Tb consists of a dominant peak at 544 nm when excited with UV radiations. Thermoluminescence (TL) peaks at approximately 140 °C, 245 °C and 458 °C are observed in the CaAl12O19:Tb phosphor. Investigations using the technique of electron spin resonance (ESR) were carried out to study the defect centers induced in the phosphor by γ-ray irradiation. ESR study reveals the presence of several distinct centers. One of the centers (center I) with an isotropic g factor 2.0110 is tentatively assigned to an intrinsic O− type center and this center relates with the TL peak at 140 °C. Center II with an axially symmetric g-tensor with principal values g ∥ = 2.0324 and g ⊥ = 2.0060 is attributable to an O2 − ion and also appears to correlate with the 140 °C TL peak. Several F+-centers have been identified and their correlation with the observed TL peaks will be discussed.

Visible upconversion luminescence of Yb co-doped Gd2Zr2O7:Er prepared by a solution combustion reaction

Phosphor powders of Gd2Zr2O7:Er3+ and Gd2Zr2O7:Er3+, Yb3+ have been prepared by the urea combustion route. Phase evolution of the synthesized powder is determined by X-ray diffraction techniques. Near infrared to visible frequency upconversion in the doped/codoped phosphors upon CW diode laser excitation at ~978 nm have been studied and an enhancement about ~26 and ~93 times in the green and red region observed in the Gd2Zr2O7:Er3+, Yb3+ compared to that of the Gd2Zr2O7:Er3+ phosphor. Based upon the ratio of green to red emission band and fluorescence intensity ratio, energy transfer from the Yb3+ to Er3+ ions has been observed to be a dominant process responsible for this enhancement in the visible region.

Optical and EPR Properties of Mn- and Eu-Activated LaMgAl11O19 Phosphor

LaMgAl11O19 phosphor doped with Eu and Mn ions has been prepared by the urea combustion route. The as-prepared phosphor was studied using X-ray diffraction, electron paramagnetic resonance (EPR), diffuse reflectance and photoluminescence studies. The EPR spectra of LaMgAl11O19:Eu, Mn phosphor exhibit signals with the effective g values at g = 1.98, 4.29 and 7.23. The resonance signals at g = 1.98 and 4.29 were attributed to Mn2+ ions in tetrahedral and rhombic environment, respectively. The resonance signal at g = 7.23 was attributed to Eu2+ ions. The optical spectrum of this phosphor exhibits an intense band in the visible region and this band has been attributed to spin-allowed 5Eg → 5T2g transition of Mn3+ ions. Upon excitation at 324 nm, the material displays emission in the blue, green and red spectral region.

Intense up-conversion luminescence in Er3+/Yb3+ co-doped CeO2 powders

The Er3+ and Er3+/Yb3+ co-doped CeO2 powders have been prepared by a urea combustion route. The structural, morphological, compositional and vibrational analysis of the Er3+:CeO2 and Er3+/Yb3+:CeO2 powders have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and Fourier transform infrared spectroscopy. The optical and luminescence properties of Er3+:CeO2 and Er3+/Yb3+:CeO2 powders have been studied by using laser excited spectroscopy. The effects of Yb3+ doping on up-conversion luminescence of Er3+ co-doped CeO2 powders were studied. The ratio of red to green intensity is decreased in Er3+:CeO2 whereas the ratio is increased in Er3+/Yb3+:CeO2 powders with increase of power. The effect of co-doping with the Yb3+ ions on the visible luminescence of Er3+ and the energy transfer mechanism responsible for the variation in the green and red intensity are discussed. The results indicate that these materials may be suitable for display and light emitting devices.

Optical and EPR studies of Gd2Zr2O7 phosphors prepared via solution combustion method

Phosphor powder of Gd2Zr2O7 has been prepared by the urea combustion route. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) technique. The structural environment between the Gd3+ and the zirconium oxide lattice has been investigated using electron paramagnetic resonance (EPR), diffuse reflectance and photoluminescence (PL) studies. The EPR spectrum of Gd2Zr2O7 phosphor exhibits a broad and intense signal at g≈2.0 and this has been attributed to Gd3+ ions in octahedral symmetry with strong dipolar interactions between Gd3+ ions. The intensity of the spectrum increases with temperature lowering from 296 to 110K following the usual Boltzmann law. The g value is invariant with temperature variation. The diffuse reflectance spectrum exhibits two sharp and weak bands characteristic of Gd3+ ions in octahedral symmetry. The photoluminescence spectrum exhibits several bands characteristic of Gd3+ ions in octahedral symmetry.

NIR to visible frequency upconversion in Er3+ and Yb3+ codoped ZrO2 phosphor

The ZrO2:Er3+ codoped with Yb3+ phosphor powders have been prepared by the urea combustion route. Formation of the compounds ZrO2:Er3+ and ZrO2:Er3+, Yb3+ was confirmed by XRD. The frequency upconversion emissions in the green and red regions upon excitation with a CW diode laser at ∼978 nm are reported. Codoping with Yb3+ enhances the emission intensities of the triply ionized erbium in the green and red spectral regions by about ∼130 and ∼820 times respectively. The emission properties of the ZrO2:Er3+ phosphor powders are discussed on the basis of excited state absorption, energy transfer, and cross-relaxation energy transfer mechanisms.

NIR to visible frequency upconversion in Er3+ and Yb3+ co-doped BaZrO3 phosphor

Phosphor powders of Yb3+ co-doped BaZrO3:Er3+ have been prepared by the urea combustion route. The formation of single-phase BaZrO3:Er3+ and BaZrO3:Er3+,Yb3+ was confirmed by X-ray powder diffraction (XRD). Green and red luminescence along with a weaker blue emission is observed upon excitation at ∼978nm with a diode laser. These emissions are caused by frequency upconversion in the Er3+-doped BaZrO3 (BZO) phosphor. Both the green and red upconversion emissions of the Er3+ are enhanced by about ∼3 and ∼43 times respectively when triply ionized ytterbium is incorporated as a co-dopant. The frequency upconversion processes responsible for the blue, green and red emissions are discussed on the basis of the experimental data.

Intense green and red upconversion emission of Er3+,Yb3+ co-doped CaZrO3 obtained by a solution combustion reaction

CaZrO3 phosphors co-doped with Er3+ and Yb3+ ions have been prepared by the urea combustion route. The formation of the orthorhombic phase of CaZrO3 was confirmed by powder x-ray diffraction. The absorption in the 280–1800 nm region and excitation spectrum corresponding to the emission at 545 nm for CaZrO3:Er3+/CaZrO3:Er3+,Yb3+ phosphors have been recorded. Upon excitation at 978 nm, the material displays strong energy transfer upconversion emission in the green and red spectral regions. The upconversion emission of the CaZrO3:Er3+,Yb3+ co-doped material shows an increased red-to-green ratio, indicating cross relaxation between Er3+ ions.

EPR and photoluminescence properties of Mn 2+-activated zinc gallate phosphor prepared by urea combustion route and post heat treatment

Mn 2+ activated ZnGa 2O 4 powder phosphors have been prepared by urea combustion route. Powder X-ray diffraction and scanning electron microscopy (SEM) techniques have been used to characterize the as-prepared and post-treated (900 °C, 3 h) phosphors. The morphology shows small particles, voids and pores, with non-uniform shapes and sizes. The EPR spectrum exhibits an intense resonance signal at g≈1.985 with a sextet hyperfine structure (hfs) besides a weak broad signal at g≈4.05 and a hump near g≈2.27. The g≈1.985 resonance is due to Mn 2+ ions in an environment close to tetrahedral symmetry. The resonances at g≈4.05 and 2.27 are attributed to the rhombic surroundings of the Mn 2+ ions. The spin concentration ( N) and the paramagnetic susceptibility ( χ) are evaluated and discussed. It is observed that the intensity of the resonance signal at g≈1.985 increases with decrease in temperature obeying the Boltzmann law. Upon post treatment the intensity of the green emission ( λ em=528 nm, 4T 1→ 6A 1 transition of Mn 2+ ions) has been increased to 3.35 times and a red shift has been observed.

Green luminescence and EPR studies on Mn-activated yttrium aluminum garnet phosphor

Yttrium aluminum garnet (Y3Al5O12) and Mn activated Y3Al5O12 phosphors have been prepared by urea combustion route in less than 5 min. The phosphors are well characterized by powder X-ray diffraction, Scanning electron microscopy and Fourier-transform infrared spectroscopic techniques. Photoluminescence tests on the pure Y3Al5O12 showed a strong green emission at 525 nm (2.36 eV) attributed to the strongly allowed transition of F+ center whereas in Mn2+ activated YAG the green emission at 519 nm is due to the 4T1 (G)→6A1 (S) transition of Mn2+ ions. EPR studies have been carried out on Mn2+ activated Y3Al5O12 phosphor at 300 and 110 K. From EPR spectra the spin-Hamiltonian parameters have been evaluated. The magnitude of the hyperfine splitting (A) indicates that the Mn2+ ions are in a moderately ionic environment. The spin concentration (N) and paramagnetic susceptibility (χ) have been evaluated and discussed.

Studies on red-emitting Cr 3+ doped barium aluminate phosphor obtained by combustion process

Red-emitting BaAl 2O 4:Cr 3+ phosphor material is prepared by urea combustion route in 5 min. Powder X-ray (XRD) diffraction, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET surface area measurements are used to characterize the as-prepared combustion products. Electron Paramagnetic Resonance (EPR) studies have been carried out on Cr 3+ ions in BaAl 2O 4 phosphors at room temperature and at 110 K. The number of spins participating in resonance ( N) and its paramagnetic susceptibilities ( χ) have also been evaluated. The excitation spectra shows two broad and intense bands corresponding to Cr 3+ ion in octahedral symmetry. The red emission peak observed at 705 nm is identified as due to 2E g → 4A 2g transition from Cr 3+ ions. The crystal field parameter Dq and Racah inter-electronic repulsion parameters B and C have been evaluated. From the results and analyses of the EPR and optical studies, the site symmetry of Cr 3+ ion in this phosphor is attributed to a distorted octahedron.

Combustion synthesis and luminescence properties of MgSrAl10O17:Mn2+ and BaAl2O4:Mn4+

MgSrAl10O17:Mn2+ and BaAl2O4:Mn4+ luminescent materials were prepared by urea combustion route. Powder X-ray diffraction, scanning electron microscopy, and Brunauer-Emmet-Teller (BET) surface area measurements were used to characterize the as-prepared combustion products, while the optical properties were investigated by photoluminescence (PL) spectra. Photoluminescence studies of MgSrAl10O17:Mn2+ showed green emission from Mn2+ ions. Electron Paramagnetic Resonance (EPR) investigations also indicated the presence of Mn2+ ions in the prepared material, while photoluminescence studies of BaAl2O4:Mn4+ suggest that doped-Mn ions exist predominantly in tetravalent oxidation state in this material.

Luminescence and EPR studies of Mn-activated SrAl 12O 19 phosphor prepared by facile combustion approach

Manganese-activated strontium hexa-aluminate (SrAl 12O 19) phosphor has been prepared at low temperature (500 °C) and in a very short time (<5 min) by urea combustion route. Powder X-ray diffraction pattern showed the presence of hexagonal SrAl 12O 19 phase. Scanning electron microscopy (SEM) indicated the presence of several particles with sizes of 200 nm. The luminescence of Mn 2+ activated SrAl 12O 19 exhibits a strong green emission peak around 515 nm from the synthesized phosphor particles under excitation (451 nm). The luminescence is assigned to a transition from the upper 4T 1→ 6A 1 ground state of Mn 2+ ions. EPR investigations also indicated the presence of Mn 2+ ions in the prepared material. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The magnitude of the hyperfine splitting ( A) constant indicates that there exists a moderately covalent bonding between Mn 2+ ions and the surrounding ligands. The variation of zero-field splitting parameter ( D) with temperature is measured and discussed. The mechanism involved in the generation of a green emission has been explained in detail.

Studies on Eu doped Ba and Zn aluminate phosphors prepared by combustion synthesis

BaAl2O4:Eu2+ and ZnAl2O4:Eu3+ phosphors were prepared by urea combustion route. The formation of crystalline aluminates was confirmed by X-ray diffraction. The X-band EPR spectra of BaAl2O4:Eu2+ showed the presence of Eu2+ ions, while in the case of ZnAl2O4:Eu3+, no signal attributable to Eu2+ was observed. The broad band UV excited luminescence of BaAl2O4:Eu2+ was observed at the blue region (λmax=439nm) due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion, whereas ZnAl2O4:Eu3+ gave an emission at 613nm attributed to 5D0–7F2 transition of Eu3+ ions.

Zirconia-spinel composites. Part I: synthesis of powders and dense materials

MgAl 2O 4 and x wt% ZrO 2–MgAl 2O 4 (1 ≤ x ≤ 30) composite powders were prepared by the urea combustion route. The powders were further ground by either ball milling or attrition to refine the grain size. Zirconia was found solely in the tetragonal form. Dense materials were prepared by hot pressing. The spinel matrix grains were submicronic in size. The ZrO 2 particles were homogeneously dispersed at the grain junctions of the matrix, and their average size increased from less than 0.20 μm to ca. 0.45 μm with increasing content of ZrO 2. The formation of monoclinic ZrO 2 particles proceeded accordingly, being easier in materials with a finer matrix grain size (ex-attrition).