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Chromium-doped \(\alpha\)-\(\hbox {Al}_{2}\hbox {O}_{3}\) powder was synthesized by a modified sol–gel method using poly(vinyl alcohol) aqueous solutions and metal nitrate precursors. The synthesis process is simple, is of low cost and produced final crystals with cubic shape as confirmed by X-ray diffraction. The morphology of the samples verified...
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... curve of the aluminum oxide sample synthesized shows only two weight losses, as presented in Fig. 1. The first weight loss, from room temperature to about 160 • C , corresponds to water evaporation. The second, from 160 to 550 • C , occurs from decomposition of organic materials and the formation of the alumina phase. Above 556 • C , the mass remains constant. The thermogravimetric curve is shown only up to 1000 • C , because no ...
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... curve of the aluminum oxide sample synthesized shows only two weight losses, as presented in Fig. 1. The first weight loss, from room temperature to about 160 • C , corresponds to water evaporation. The second, from 160 to 550 • C , occurs from decomposition of organic materials and the formation of the alumina phase. Above 556 • C , the mass remains constant. The thermogravimetric curve is shown only up to 1000 • C , because no ...
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We have synthesized CuO and Cu 2 O nanoparticles by sol-gel method for possible applications in photo-voltaic or energy storage devices. XRD pattern clearly indicates the formation of pure CuO and Cu 2 O nanostructures with an average crystallite size of 31.9 and 39.3 nm, respectively. FTIR spectroscopy analysis also confirms the formation of pure...
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... The room temperature (300K) emission spectra of Cr-doped Al 2 O 3 -YAG/Al 2 O 3 -YAG-ZrO 2 eutectics in the wavelength range of 600-900 nm are recorded under green (532 nm) and blue excitation light (450 nm) are shown in Fig. 10. Under the green excitation, Cr-doped Al 2 O 3 is clearly identified [38]. The sharp line centered at 694 nm corresponds to the forbidden transitions spin from 2 E to 4 A 2 level, referred to R-line, and the broad band centered at 774 nm is due to the phonon-assisted 4 T 2 to ground state 4 A 2 . ...
... This last transition was mostly observed when Cr-doped Al 2 O 3 is higher than 0.5 at%. Indeed, the relative intensity of broad band centered at 774 nm is increasing with the concentrations [38]. This effect is magnified in Cr-doped ternary eutectics. ...
... For this wavelength, the decay curves are particularly non-exponential due to the competition of the relaxation process from the excited level to the emitting 4 T 2 level and the partial thermal equilibrium with the 2 E levels. However, this thermal coupling being less efficient at low temperature (77 K), it is observed that the values of decay times of the 4 T 2^4 A 2 allowed transition measured at 773.0 nm becomes shorter than at 300 K. Finally, the decay time of Crdoped binary eutectics is in good agreement with Cr 3+ :Al 2 O 3 powder [38], and Ruby bulk crystals [40] especially considering the lifetime of about 1ms for 2 at% of the Cr-Cr pair emission of the N-lines measured at 704nm under 532 nm at low temperature. It is interesting to note that the lifetime of the emission of Cr pairs is much shorter in the ternary 0.3ms than in the binary eutectics 0.8 ms. ...
Cr -doped Al2O3-YAG and Al2O3-YAG-ZrO2 eutectic ceramics rods of 3mm in diameter were solidified from the melt by micro-pulling down (µ-PD) technique. The Cr dopant affect the microstructure and the...
... Many methods to obtain YAG have been reported [14,30]. In particular, a modified sol-gel method using poly(vinyl alcohol) aqueous solutions and metal nitrate precursors has showed as efficient and low cost to obtain Y 3 Al 5 O 12 pure crystalline phase [31]. ...
Efficient white-emitting phosphor-in-glass (PiG) was successfully synthesized by synergistic complexation of Ce3+-doped YAG phosphor and Eu3+-doped sodium calcium silicate glass. The crystalline phosphor was obtained via sol-gel route using polyvinyl alcohol (PVA), whereas glasses were prepared by melting-quenching method. Rare-earth ions were successfully incorporated into the YAG and glass host lattices without changing their original structures. Through adjusting the Eu 3+-doped glass and Ce 3+ :YAG phosphorus contents in the PiG, it was possible to optimize the chromaticity emission from yellow-green to orange-red in CIE 1931 diagram. Combination of a violet LED and samples emissions, allowed to achieve the chromaticity parameters closer to an ideal white light source [CIE-(0.33, 0.33); CCT 5000K]. Moreover, adjusting the luminescence intensity ratio between the LED and the PiG emission provides a tuning route for smart white light devices.
... Ruby is a gemstone formed by doping α-Al 2 O 3 single crystal with a small amount of Cr 3+ [12] and has been used in different applications in physics such as optoelectronics and lasers [13]. Capeloto et al. have reported that nano α-Al 2 O 3 doped with Cr up to 2 wt% emitted a red color [14]. In addition, Grigorjeva et al. have prepared α-Al 2 O 3 / Cr powders through DC reactive-magnetron sputtering with subsequent milling and oxidation; the dosimetric characteristics of those powders have shown sensitivity along a dose range extending to 20 kGy with a linear response up to 6 kGy [15]. ...
Cr-doped α-Al2O3 samples (Al2-xCrxO3,) were synthesized by citrate-precursor autocombustion method. The lattice parameters, bond distortion index, crystallite size and lattice microstrain of the developed system were investigated using Rietveld profile method. The porous nature of the formed samples was elucidated by a scanning electron microscope. The effect of doping on the vibrational band positions was examined using Fourier-transform infrared technique. The photoluminescence emission showed that a red color was mainly exhibited by all samples, while that with x = 0.05 showed the highest intensity. Other colors appear with a small intensity for higher Cr-doped samples. The electronic, optical, and mechanical-stability properties of undoped and doped samples were investigated using density-function theory calculation.
In this work, we report the color tunable photoluminescence in the Cr³⁺/Li⁺ doped and co-doped ZnGa2O4 (ZGO) phosphors synthesized by solid state reaction method. The phase and surface morphology of ZGO phosphor were examined by XRD and SEM measurements, respectively. The EDS spectra revealed the presence of Zn, Ga, Cr and O elements in the phosphor. The vibrational structure of the phosphor materials has been analyzed by FTIR measurements. The Cr³⁺ doped phosphor shows electronic absorption bands at 302, 408 and 544 nm alongwith the host CTB at 260 nm. The optical band gap of the phosphor decreases via doping of Cr³⁺ and Cr³⁺/Li⁺ ions. The ZGO is a self-activated host and emits broad blue emission with maximum at 434 nm upon excitation at 260 nm. The Cr³⁺ doped phosphors show emission bands due to spin-allowed as well as spin-forbidden transitions due to Cr³⁺ ion in the blue, green and NIR regions on excitation with 260, 302, 408 and 544 nm wavelengths. The emission intensity is optimum for 0.5 mol% concentration of Cr³⁺ ion. The emission intensity of Cr³⁺ doped ZGO phosphor increases via doping of Li⁺ ion. The color tunability has been observed in the phosphor upon 260 and 302 nm excitations. The lifetimes of ⁴T2 (⁴F) and ²E states of Cr³⁺ ion have been measured and it is found that it decreases with increasing concentrations of Cr³⁺ and Cr³⁺/Li⁺ ions. The Cr³⁺/Li⁺ doped and co-doped ZGO phosphors may be suitable candidates for display devices, solid state lighting and NIR LEDs.
The effect of triple doping with chromium, lanthanum and barium on the mechanical, degassing and gas diffusion properties of fine-crystalline corundum synthesized in a supercritical water fluid was studied. The influence of chromium monodoping on the mechanical and optical properties of fine-crystalline corundum was also investigated. It was found that even small amounts of dopants of lanthanum and chromium during triple and monodoping of corundum significantly improve its mechanical properties (increase the abrasive ability) and reduce it several times the content of volatile gas-liquid impurities, which contributes to increase transparency of the resulting ceramics. The role of the interaction of a chromium impurity with oxygen vacancies in corundum on the increase in the static strength of crystals was suggested. The diffusion coefficients of water in doped corundum were determined. Comparison of the degassing and diffusion properties of corundum doped with La, Cr, Ba with undoped corundum and corundum doped with lanthanum was carried out. The results obtained contribute to the creation of new materials based on doped corundum with high abrasive, luminescent, and gas diffusion characteristics.
The luminescence of Al2O3:Cr³⁺ is the foundation for advancement of modern laser technology. Preparation of Al2O3:Cr³⁺ materials through combustion method is known as simple, cost-effective and short-time consuming approach. The types of fuel use in this method has a significant effect on the combustion products. In our research, urea, glycine and sorbitol were used as a fuel in order to study their effect on the physical, structural and photoluminescence properties of Al2O3:Cr³⁺ powders. These powders were characterized by scanning electron microscope (SEM), energy dispersive x-ray (EDX) spectroscopy, x-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. SEM micrograph of Al2O3:Cr³⁺ powders using urea and sorbitol fuels show the powders obtained are highly agglomerated slab-like particles with typical thickness 2-5 µm. Meanwhile, the powder prepared using glycine fuel is observed to be agglomerated particles with tiny porous morphology. EDX results are in good agreement with the original chemical composition of the elements. Based on XRD results, all produced samples contain α-Al2O3 phase (COD-ID: 9008081) crystalline structure. However, the sample synthesized using sorbitol and glycine show the existence of additional Al2O3 phase crystalline structure which are γ-Al2O3 cubic phase (COD-ID: 1541582) and θ-Al2O3 monoclinic phase (COD-ID: 2107302). The crystallite size was estimated using Scherer’s formula and found to be 40.97, 28.94 and 31.23 nm for urea, sorbitol and glycine respectively. To acquire better comparison, another method was used to calculate crystallite size which is Williamson-Hall (W-H) plots. Crystallite size was estimated to be 82.20, 47.45 and 49.53 nm for urea, sorbitol and glycine, respectively. PL of the sample that synthesized using urea as fuel shows higher intensity compared to sorbitol and glycine as fuel. The peak at 405 nm shows higher excitation intensity compared to peak at 557 nm which are better excitation for the Al2O3:Cr³⁺ powders. From photoluminescence spectra, all samples show sharp emission spectra at 694 nm and sample prepared using urea produce highest emission intensity. Moreover, the samples synthesized with urea fuel showed the formation of highly crystalline Al2O3:Cr³⁺ powder and fully formed α-Al2O3 phase. Thus, it can be concluded that the sample produced using urea as fuel have better luminescence properties compared to other samples.
