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Abstract: Results of structural and spectroscopic measurements of Sm3+ doped calcium aluminates: Ca1−x Sm x Al4O7 and Ca1−2x Sm x Na x Al4O7 (x=0.0005, 0.002, 0.01, 0.02, 0.03, 0.05) obtained by the modified Pechini method are presented. All samples yield intense orange–red emission under violet excitation (404.5nm). Narrow bands corresponding to characteristic f–f intraconfigurational transition of Sm3+ in excitation and emission spectra were observed. The influences of the concentration of Sm3+ as well as charge compensation by co-doping with Na+ ions on the luminescent properties of the phosphor were investigated. Detailed analysis of the emission spectra of Sm3+ doped and Sm3+,Na+ co-doped CaAl4O7 powders proved that activator ions substitute Ca2+ in the host. Co-doping with Na+ ions enhanced greatly the intensity of the luminescence. Concentration dependencies of the intensity of luminescence and its decay kinetics proved the emission quenching at higher dopant contents due to cross-relaxation processes between Sm3+ ions. Fitting of the 4G5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes. [Copyright &y& Elsevier]

Abstract: Nanocrystallic europium-activated lutetium oxide (Lu2O3:Eu) is a strong candidate for use in digital medical imaging applications, due to its spectroscopic and structural properties. The aim of the present study was to investigate the imaging and efficiency properties of a 33.3mg/cm2 Lu2O3:Eu scintillating screen coupled to a high resolution RadEye HR CMOS photodetector under radiographic imaging conditions. Since Lu2O3:Eu emits light in the red wavelength range, the light emission efficiency and the imaging performance were compared with results for a Gd2O2S:Eu phosphor screen. Parameters such as the Absolute Efficiency (AE), the X-ray Luminescence Efficiency (XLE), and the Detector Quantum Gain (DQG), were investigated. The imaging characteristics of Lu2O3:Eu nanophosphor screen were investigated in terms of the Modulation Transfer Function (MTF), the Normalized Noise Power Spectrum (NNPS) and the Detective Quantum Efficiency (DQE). It was found that Lu2O3:Eu nanophosphor has higher AE and XLE by a factor of 1.32 and 1.37 on average, respectively, in the whole radiographic energy range in comparison with the Gd2O2S:Eu screen. DQG was also found higher in the energy range from 50kVp to 100kVp and comparable thereafter. The imaging quality of Lu2O3:Eu nanophosphor coupled to the CMOS sensor was found to outmatch in any aspect in comparison with the Gd2O2S:Eu screen. These results indicate that Lu2O3:Eu nanophosphor could be considered for further research in order to be used in medical imaging applications. [Copyright &y& Elsevier]

Abstract: Two series of calcium aluminates: Singly doped CaAl4O7:Yb(x%) and co-doped CaAl4O7:Yb(x%),Na(x%) (x=0.002, 0.01, 0.02, 0.04, 0.05, 0.06, 0.07, 0.1) were synthesized by a modified Pechini citrate process and their optical properties at 298K and 77K were investigated. Direct excitation of Yb3+ by means of 2F7/2→2F5/2 absorption at 940–980nm leads to a reversed 2F5/2→2F7/2 transition giving Yb3+ emission in the range of 970–1130nm as well as bluish-green up-converted (UC) luminescence whose energy doubles that of the near-IR (NIR) one. The UC luminescence was characterized by absorption and emission spectra, decay time measurements as well as its intensity dependence on the pumping power. The effect of dopant concentration and charge compensation by co-doping with Na+ ions on morphology and luminescent properties were also studied. The co-doping affected the luminescence behavior but had no influence on the powders morphology. Na+ addition led to narrowing of NIR luminescence bands, suggesting smaller disturbance of Yb3+ ions local symmetries and also significantly enhanced NIR and UC luminescence of Yb3+. [Copyright &y& Elsevier]

Abstract: Comparative analysis of the luminescent properties of Y3Al5O12:Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where YAl antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of YAl antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200–470nm range related to YAl antisite defects and charged oxygen vacancies (F+ and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce3+ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce3+ ions. [ABSTRACT FROM AUTHOR]