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The synthesis of Ce-doped Gd oxyorthosilicate nanoparticles using the solution combustion synthesis (SCS) method was investigated as a function of the amount of SiO2 in the precursor mixture. The SCS product consists of mixtures of Ce-doped Gd2SiO5, Gd4.67(SiO4)3O, and Gd2O3, whose relative concentrations depend on the amount of SiO2 in the precursor mixture; the synthesis of GSO:Ce was obtained with a reduction by 30% of the SiO2 content. Accordingly, this is the brightest material produced, with a photoluminescence signal that is comparable to that obtained from the bulk sample. Thermoluminescence (TL) results showed a considerably lower concentration of trapping defects in the nanoparticles than in the bulk sample. A previous study [E. G. Yukihara, L. G. Jacobsohn, M. W. Blair, B. L. Bennett, S. C. Tornga, and R. E. Muenchausen, J. Lumin. 130, 2309-2316 (2010)] reporting a comparison between photoluminescence and scintillation measurements, coupled to the TL characterization, suggests that surfaces play a major role in decreasing the scintillation efficiency of the nanoparticles. These results show that it is possible to prepare relatively bright scintillator powders using the SCS method. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL), radioluminescence (RL), and thermoluminescence (TL) investigation of Y2O3:Bi nanophosphors prepared by solution combustion synthesis using urea, glycine, and hexamethylenetetramine (HMT) as fuels was carried out. The as-prepared nanopowders have increasing crystallinity and average crystallite sizes for urea, glycine, and HMT, respectively. Luminescence is composed of two emission bands centered at 408 and 505 nm due to two nonequivalent Bi3+ sites with symmetry S6 and C2, respectively. The occupancy of these sites depends on the synthesis conditions, in agreement with theoretical predictions. Annealing at 1000 °C for 1 h improves PL and RL efficiency due to enhanced crystallinity of the nanopowders and activation of recombination centers (Bi3+ ions). No shift in the PL peak position was observed as a function of average crystallite size. The concentration quenching was experimentally determined to have a maximum emission of around 3 mol % of the dopant. TL spectra present several peaks between 50 and 300 °C, and the total TL signal is correlated with the heat of combustion of the fuel and thus crystallinity increases. Most likely, increases in RL and TL are also due to the increase in the concentration of recombination centers. [ABSTRACT FROM AUTHOR]

The synthesis, structural, luminescent, and magnetic properties of multifunction 8 at. % Eu-doped Gd2O3 nanocrystals were investigated. The material was synthesized by the solution combustion technique and characterized by x-ray diffraction (XRD), transmission electron microscopy, and photoluminescence and magnetization measurements. The as-prepared material presents predominant base-centered monoclinic structure with average crystallite size of 35 nm. Isothermal annealing at 1000 °C for up to 152 h induced gradual structural transition toward the body-centered cubic structure. Debye–Scherrer analysis of XRD results showed that annealing did not induce grain growth of monoclinic nanocrystals, while cubic nanocrystals reached 47 nm after annealing for 152 h. The luminescent behavior was monitored as a function of annealing time and related to the structural transformation. In particular, an inversion of the predominant photoluminescence emission line from 621.4 to 609.5 nm was observed and related to changes in the crystalline field resultant to phase transformation from cubic to monoclinic. Magnetic measurements revealed the paramagnetic nature of the material, much insensitive to the crystallographic structure. [ABSTRACT FROM AUTHOR]

The effects of ion irradiation on porous Si (po-Si) photoluminescence (PL) are investigated to gain insight into the emission mechanism. Po-Si was obtained by standard electrochemical etching of p-doped Si(100) and the samples were aged for several weeks to achieve stability of the PL intensity. Specimens were progressively irradiated with H+, He+, or Ne++ ions followed by PL measurements. PL spectra were obtained as a function of the displacement per atom (DPA) parameter up to a DPA level of ∼10-2, which was sufficient to nearly extinguish PL. The quenching behavior showed a strong dependence on the chemical nature of the implanted species. Within experimental error, the quenching efficiency was equivalent for He+ and Ne++ irradiations, but was considerably higher for H+ irradiation. Channeling spectrometry showed the efficiency to be correlated with the self-recovery of defects generated during irradiation. The observed PL quenching is associated with the creation of nonradiative recombination sites within the band gap, but not with Si nanostructure amorphization and/or surface oxygen removal. Significant recovery of quenched PL occurs over a period of 120 days for specimens that are stored in air, but not for samples that are stored in vacuum. These results demonstrate the importance and complexity of surface oxidation on the po-Si luminescence mechanism. [ABSTRACT FROM AUTHOR]

Presents information on a study that investigated film orientation by x-ray diffraction and transmission electron microscopy for YBCO films grown on unbuffered and CeO[sub2]-buffered yttria-stabilized zirconia. Experimental procedures; Results and discussion; Conclusions.

Deals with a study of the surface topography of YBa[sub2]Cu[sub3]O[sub7] thin films prepared by pulsed laser deposition by atomic force microscopy and scanning tunneling microscopy. Results and discussion; Conclusions.

The effects of ion irradiation on porous Si (po-Si) photoluminescence (PL) have been investigated. Specimens were progressively irradiated with H+ and He+ ions followed by PL measurements. After the final irradiation, which resulted in total PL quenching, PL recovery was monitored for more than 200 days. The behavior of both PL quenching and recovery was correlated to the amount of retained irradiation-induced damage, determined by channeling spectrometry measurements, and to the chemical nature of the implanted species. Quenching was attributed to the generation of defects that create nonradiative states within the gap, while recovery was attributed to the passivation of these defects by atmospheric exposure. H+ irradiation is approximately five times more efficient in quenching PL and leads to approximately four times lower recovery rate than He+ irradiation. This behavior is attributed to the formation of stable H-defect complexes. [ABSTRACT FROM AUTHOR]

Presents a study that examined properties of thin films upon low fluence laser irradiation. Method of the study; Results and discussion; Conclusion.