Absolute Luminescence Efficiency Research Articles

Efficiency of Lu 2SiO 5:Ce (LSO) powder phosphor as X-ray to light converter under mammographic imaging conditions

The aim of the present study was to examine the light emission efficiency of Lu 2SiO 5:Ce (LSO) powder scintillator under X-ray mammographic imaging conditions. Powder LSO scintillator has never been used in X-ray imaging. For the purposes of the present study, a 25 mg/cm 2 thick scintillating screen was prepared in our laboratory, by sedimentation of Lu 2SiO 5:Ce powder. Absolute luminescence efficiency measurements were performed within the range of X-ray tube voltages (22–49 kVp) used in mammographic applications. Parameters related to X-ray detection, i.e. the energy absorption efficiency (EAE) and the quantum detection efficiency (QDE) were calculated. A theoretical model, describing radiation and light transfer, was employed to fit experimental data and to estimate values of the intrinsic conversion efficiency and the light attenuation coefficients of the screen. The spectral compatibility of the LSO powder scintillator to mammographic X-ray films and to various electronic optical detectors was determined by performing light emission spectrum measurements and by taking into account the spectral sensitivity of the optical detectors. Results in the voltage range used in mammography showed that Lu 2SiO 5:Ce powder scintillator has approximately 10% higher values of QDE and 4.5% higher values of EAE than Gd 2O 2S:Tb.

Luminescence efficiency of Gd/sub 2/SiO/sub 5/:Ce scintillator under X-ray excitation

Gd/sub 2/SiO/sub 5/:Ce (GSO:Ce) is a high-Z, nonhygroscopic fast emitting scintillator used in detectors of positron emission tomography (PET) systems. The purpose of this study was to evaluate the luminescence efficiency of GSO:Ce scintillator under irradiation conditions employed in X-ray medical imaging, since findings may be of value in novel applications such as computed tomography breast imaging or modern fast image producing X-ray computed tomography. To this aim the absolute luminescence efficiency (emitted light flux over X-ray exposure), the spectral matching factor (compatibility to optical detectors), and the effective efficiency (the product of absolute efficiency and spectral compatibility) were determined for X-ray tube voltages ranging from 20 to 140 kV. The efficiency of GSO:Ce was found to increase with increasing X-ray tube voltage, while the GSO:Ce spectrum, peaking at 440 and 490 nm, was found compatible to most optical detectors (photodiodes, photocathodes, and charge-coupled devices).

Absolute luminescence efficiency and photonic band-gap effect of conjugated polymers with top-deposited distributed Bragg reflectors

We study the effects of the deposition of a photonic crystal (PhC) structure, namely a distributed Bragg reflector, on a light-emitting conjugated polymer. The hybrid organic/PhC system is realised by a novel low-temperature reactive electron beam deposition, suitable for the direct fabrication of high-reflective mirrors onto organic soft matter. We investigated the photoluminescence absolute quantum efficiency of the system, finding a yield of 30% after the mirror deposition. We found evidence for the modulation of the output spectra by the photonic band-gap of the coupled PhC, and for the polarisation splitting (as large as 140 meV) of the emitted light.

Light emission efficiency and imaging performance of Y3Al5O12: Ce (YAG: Ce) powder screens under diagnostic radiology conditions

In this study Y3Al5O12: Ce powder scintillator was evaluated for use in X-ray imaging detectors. This phosphor, also known as YAG: Ce scintillator or P-46 phosphor, is a non-hygroscopic, emitting green light with very short decay time. These properties are very attractive for X-ray imaging. Y3Al5O12: Ce powder was used to prepare various test screens (33–166 mg/cm2). Absolute luminescence efficiency measurements were performed for various X-ray tube voltages (50–130 kVp). In addition parameters related to image quality such as the modulation transfer function and the detective quantum efficiency were examined. A theoretical model, describing radiation and light transfer, was employed to fit experimental data and to estimate values of optical parameters. Absolute efficiency was found to decrease with X-ray tube voltage. Highest efficiency was obtained for the 107 mg/cm2 screen. Light attenuation coefficients were close to those of green emitting rare earth scintillators. At low spatial frequencies the detective quantum efficiency was high for the 107–166 mg/cm2 screens. The light emission efficiency and imaging performance of Y3Al5O12: Ce was not better than currently employed scintillators. However due to its very fast response and high spectral compatibility to optical sensors it may be considered for use in digital imaging detectors.

Electrogenerated chemiluminescence. Determination of the absolute luminescence efficiency in electrogenerated chemiluminescence. 9,10-Diphenylanthracene-thianthrene and other systems

Electrogenerated chemiluminescence. Determination of the absolute luminescence efficiency in electrogenerated chemiluminescence. 9,10-Diphenylanthracene-thianthrene and other systems