Nanostructured Yb:GGG polycrystalline powders via gel combustion method

Gadolinium gallium gamet （GGG） nanopowders doped with ytterbium ions （Yb：GGG） were synthesized with citric acid as a fuel via gel combustion method. The optimized conditions for preparing yb^3＋：Gd3Ga5O12 nanopowders were discussed. The heat behavior, structure and morphology of powders were analyzed with thermal analysis （TG-DTA）, X-ray diffraction （XRD）, infrared spectra OR） and transmission electron microscope （TEM）. TG-DTA analysis revealed that the weight loss of the precursor occured below 800 ℃ and its crystallization temperature was 830.6℃. XRD and IR analysis showed that the precursor converted directly into pure GGG at a relatively lower temperature （900 ℃） without any other intermediate phase. The lattice constant was 1.2377 calculated by extrapolation method. TEM results indicated that the spherical powders showed good dispersity and had a relatively narrow size distribution with average particle size of approximately 40-50 ran, which was favorable for good sinterability of Yb：GGG laser ceramic.

Luminescence Characterization and Synthesis of γ-LiAlO_2:Eu^(3+) by Gel Combustion

γ-LiAlO2：Eu3＋（Eu3＋：LAO） phosphor was obtained by gel combustion method using LiNO3,Al（NO3）3·9H2O,Eu（NO3）3·6H2O and citric acid as raw materials.The structure,morphology and luminescence were characterized by means of X-ray diffraction （XRD）,scanning electron microscopy （SEM）,photoluminescence （PL）.The results demonstrated that the phosphor was pure-phase of flaky tetragonal crystal system with a mean size of around 1 μm.The strongest excitation peak was at 254 nm,belonging to the broadband excitation and the maximum emission peak was at 613 nm,corresponding to the 5D0→7F2 transition of Eu3＋.Luminous intensity is closely related to the calcination temperature and doping concentration of Eu3＋.

Microwave gel combustion synthesis and sinterability of Nd:GGG nanopowders

Neodymium doped gadolinium gallium oxide （Nd：GGG） nanopowders synthesized by microwave gel combustion using alanine as a fuel was reported. Metal nitrates solution with alanine fuel was combusted in microwave to give precursor. The micro-wave precursor powder was calcined at different temperatures from 800 to 1100 ℃. Phase pure Nd：GGG formation took place at 800 to 1100 ℃ as observed by X-ray diffraction （XRD） and Fourier transform infra-red （FTIR） spectroscopy. However particle size in-creased with calcinations temperature from 25 nm at 800 ℃ to 200 nm at 1100 ℃.Nd：GGG nanopowder obtained at different calci-nation temperatures were compacted and sintered at 1550 ℃ for 3 h in air. Most densified ceramic was obtained from Nd：GGG nanopowder calcined at 1100 ℃. Microstructure as observed from scanning electron microscopy （SEM） showed that the most densi-fied ceramic, obtained from nanopowder calcined at a higher calcination temperature, had a more uniform grain-size distribution, fewer pores and greater densification. XRD of sintered sample showed retention of phase purity.

Combustion synthesis and enhanced 1.5 μm emission in Y_2O_3:Er^(3+) powders codoped with La^(3+) ions

Er3+ and La3+ codoped Y2O3 nanocrystalline powders were synthesized by gel combustion method and characterized with thermal analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) techniques and fluorescence spectroscopy. After being calcined at 1200 oC, the (Y1–xLax)2O3:Er3+ powders were confirmed to be cubic Y2O3 phase with the crystalline grain size in the range of 20–40 nm. The Er3+ emission at 1.53μm from the4I13/2→4I15/2 transition was observed, which was found to be enhanced by introducing La3+ ions. Such enhancement could be attributed to the adjustment of Er3+ ions’ local environment by the codoping of La3+ ions, leading to the increased ground state absorption cross section of Er3+ ions.

Thermoluminescence glow curve analysis and kinetic parameters of Dy-doped BaSi_(2)O_(5)phosphor

In this paper,Dy^(3+)incorporated BaSi_(2)O_(5)phosphors were synthesized by gel co mbustion method and characterized by X-ray diffraction(XRD).The effects of various heating rate s on thermoluminescence(TL)kinetics and glow peak temperatures of Dy^(3+)incorporated BaSi_(2)O_(5)phosphors exposed toβirradiation at room temperature were investigated.The glow curves of the phosphor exposed toβ-irradiation(0.1-100 Gy)consist of four main peaks located at 87,130,271,and 327℃and exhibit a good linearity between 0.1 and100 Gy.Three experimental techniques including variable heating rate(VHR),repeated initial rise(RIR),peak shape(PS)and computerized glow curve deconvolution(CGCD)were employed to determine TL kinetic parameters.Our findings indicate that the TL glow peaks of the phosphor obey first-order kinetics.Analysis of the main dosimetric peaks through the techniques mentio ned above indicates that activation energies(E)and pre-exponential factor(s)are in the range of 0.80-1.50 eV and 1.15×10^(8)-3.28×10^(13)s^(-1).Additionally,it is found that the temperature of the glow peaks shifts toward the higher temperatures and the TL intensity smoothly decreases as the heating rate increases.The effect on the TL intensities and glow peak temperatu res of the heating rate is discussed in terms of thermal quenching.

Effect of Li＋ ion concentration on upconversion emission and temperature sensing behavior of La2O3：Er3＋ phosphors

The effects of Li~＋ co-doping concentration on the structure, upconversion luminescence and temperature sensing behavior of Er^（3＋）：La_2O_3 phosphors were investigated. X-ray diffraction and scanning electron microscopy observations reveal that Li~＋ ion co-doping can change the lattice parameter of La_2O_3 host and increase the particle size of the samples. The optical investigation shows that co-doping of Li~＋ ions can enhance the upconversion emission of Er^（3＋） ions in La_2O_3 matrix effectively. Most importantly, the temperature sensing sensitivity of the samples is found to be dependent on Li~＋ co-doping concentration,when the emission intensity ratio of the（~2H_（11/2）→~4 I_（15/2）） and（~4 S_（3/2）→~4 I_（15/2）） transitions of Er^（3＋） is chosen as the thermometric index. Both of the optimum upconversion luminescence and temperature sensing sensitivity are obtained for 7 mol% Li~＋ co-doped sample. When the Li~＋ concentration is beyond 7 mol%,both the quenching in upconversion intensity and the degradation of temperature sensitivity are observed, which may be due to the serious distortion in local crystal field around Er^（3＋） ions caused by the excess Li~＋ ions.