Marvin J. Weber

Inorganic scintillators: today and tomorrow

Abstract The past half-century has witnessed the discovery of many new scintillator materials and numerous advances in our understanding of the basic physical processes governing the operation of inorganic scintillators. These developments are reviewed briefly, but then the question arises—what about today and tomorrow? Have we exhausted luminescence phenomena and the periodic table in our search for improved scintillator materials? Properties of both intrinsic and activated scintillator materials, crystalline and amphorous, are considered. Several fundamental limits of scintillator performance are examined together with the prospects for discovering better scintillators guided by first-principles theoretical calculations of the processes active in scintillation.

The Quest for the Ideal Inorganic Scintillator

The past half century has witnessed the discovery of many new inorganic scintillator materials and numerous advances in our understanding of the basic physical processes governing the transformation of ionizing radiation into scintillation light. Whereas scintillators are available with a good combination of physical properties, none provides the desired combination of stopping power, light output, and decay time. A review of the numerous scintillation mechanisms of known inorganic scintillators reveals why none of them is both bright and fast. The mechanisms of radiative recombination in wide-band gap direct semiconductors, however, remain relatively unexploited for scintillators. We describe how suitably doped semiconductor scintillators could provide a combination of high light output, short decay time, and linearity of response that approach fundamental limits.

Inorganic phosphors : compositions, preparation and optical properties

Inorganic Phosphors: Compositions, Preparation and Optical Properties addresses practical and theoretical aspects of inorganic phosphors used in lighting and display applications. Authors Yen and Weber present the synthesis of phosphors in a ...cookbook... style that features nearly 300 ...recipes... using the most up-to-date guidelines and methods. They also categorize nearly 500 phosphors in terms of chemical composition and luminescence output wavelengths, summarizing their physical and emissive optical properties. This book is the first of its kind to provide a combined practical and technical foundation that can be used in commercial and academic research and development of new phosphors and applications.

Temperature dependence of the fast, near-band-edge scintillation from CuI, HgI2, PbI2, ZnO:Ga and CdS:In

Abstract We present temperature-dependent pulsed X-ray data on the decay time spectra, wavelengths, and intensities of fast (ns) radiative recombination in five direct, wide-bandgap semiconductors: CuI, HgI 2 , PbI 2 , and n-doped ZnO:Ga and CdS:In. At 12xa0K the luminosity of powder samples is 0.30, 1.6, 0.40, 2.0, and 0.15, respectively, relative to that of BGO powder at room temperature. Increasing the temperature of CuI to 346xa0K decreases the luminosity by a factor of 300 while decreasing the fwhm of the decay time spectra from 0.20 to 0.11xa0ns. Increasing the temperature of HgI 2 to 102xa0K decreases the luminosity by a factor of 53 while decreasing the fwhm from 1.6 to 0.5xa0ns. Increasing the temperature of PbI 2 to 165xa0K decreases the luminosity by a factor of 27 while decreasing the fwhm from 0.52 to 0.15xa0ns. Increasing the temperature of ZnO:Ga to 365xa0K decreases the luminosity by a factor of 33 while decreasing the fwhm from 0.41 to 0.21xa0ns. Increasing the temperature of CdS:In to 295xa0K decreases the luminosity by a factor of 30 while decreasing the fwhm from 0.20 to 0.17xa0ns. All emission wavelengths are near the band edge. The luminosities decrease much faster than the radiative lifetimes, therefore, the reduction in luminosity is not primarily due to thermal quenching of the excited states, but mostly due to thermally activated trapping of charge carriers on nonradiative recombination centers. Since the radiative and nonradiative processes occur on different centers, increasing the ratio of radiative to nonradiative centers could result in a class of inorganic scintillators whose decay time and radiative efficiency would approach fundamental limits (i.e.

Effects of Ce concentration on scintillation properties of LaBr/sub 3/:Ce

In this communication we report on our investigation of scintillation properties of LaBr/sub 3/:Ce as a function of Ce concentration. We have studied crystals nominally doped with 0.5, 5, 10, 20, and 30% Ce (by mole). Reports published so far suggested that as the Ce content increases, there is a decrease in light output and little or no change in decay time constants. Our results show that the light output does not change with Ce concentration up to 30% and depends mostly on the crystal and measurement quality. On the other hand we have found timing properties to be a strong function of concentration. As the Ce content increases the principal decay time constant of scintillation decreases from /spl sim/26 ns for 0.5% Ce to /spl sim/17 ns for crystals with >5% Ce. Moreover, there is also a significant change in rise time constants. The rise time measured for a sample doped with 0.5% Ce is up to 9 ns, whereas for samples doped with >10% Ce it reduces to less than 0.5 ns. The change of rise time has a major effect on the timing properties of this scintillator, with timing resolution improving from 390 ps to less than 200 ps (FWHM).

LaBr/sub 3/:Ce scintillators for gamma ray spectroscopy

In this paper, we report on a relatively new scintillator - LaBr/sub 3/ for gamma ray spectroscopy. Crystals of this scintillator have been grown using Bridgman process. This material when doped with cerium has high light output (/spl sim/60,000 photons/MeV) and fast principal decay constant (/spl les/25 ns). Furthermore, it shows excellent energy resolution for /spl gamma/-ray detection. Energy resolution of 3.2% (FWHM) has been achieved for 662 keV photons (/sup 137/Cs source) at room temperature. High timing resolution (260 ps FWHM) has been recorded with LaBr/sub 3/-PMT and BaF/sub 2/-PMT detectors operating in coincidence mode using 511 keV positron annihilation /spl gamma/-ray pairs. Details of its scintillation properties, and variation of these properties with changing cerium concentration are reported. Potential applications of this material are also addressed.

Design and Implementation of a Facility for Discovering New Scintillator Materials

We describe the design and operation of a high-throughput facility for synthesizing thousands of inorganic crystalline samples per year and evaluating them as potential scintillation detector materials. This facility includes a robotic dispenser, arrays of automated furnaces, a dual-beam X-ray generator for diffractometry and luminescence spectroscopy, a pulsed X-ray generator for time response measurements, computer-controlled sample changers, an optical spectrometer, and a network-accessible database management system that captures all synthesis and measurement data.

LaCl3:Ce scintillator for γ-ray detection

Abstract In this paper, we report on a relatively new cerium-doped scintillator—LaCl 3 for γ-ray spectroscopy. Crystals of this scintillator have been grown using Bridgman method. This material when doped with 10% cerium has high light output (∼50,000 photons/MeV) and fast principal decay time constant (∼20xa0ns). Furthermore, it shows excellent energy resolution for γ-ray detection. For example, energy resolution as low as 3.2% (FWHM) has been achieved with 662xa0keV photons ( 137 Cs source) at room temperature. Also, high timing resolution (264xa0ps—FWHM) has been recorded with LaCl 3 -PMT and BaF 2 -PMT detectors operating in coincidence using 511xa0keV positron annihilation γ-ray pairs. Details of crystal growth, scintillation properties, and variation of these properties with cerium concentration are also reported.

Lu2SiO5 by single-crystal X-ray and neutron diffraction.

The structure of dilutetium silicon pentaoxide, Lu2SiO5, has isolated ionic SiO4 tetrahedral units and non-Si-bonded O atoms in distorted OLu4 tetrahedra. The OLu4 tetrahedra form edge-sharing infinite chains and double O2Lu6 tetrahedra along the c axis. The edge-sharing chains are connected to the O2Lu6 double tetrahedra by isolated SiO4 units. The structure has been determined by neutron diffraction.

Prospects for dense, infrared emitting scintillators

We present results from an ongoing search for inorganic scintillators for X-ray and gamma-ray detection. We measure the scintillation properties (luminous efficiency, decay time, and emission wavelength) of powdered samples excited by brief X-ray pulses. To find scintillators that are compatible with silicon photodetectors, we have tested over 1,100 samples using a photomultiplier tube with a GaAs:Cs photocathode, which is sensitive to 200-950 nm emissions. Optical filters are used to block emissions that are observable with bialkali PMTs. Several lanthanide and transition metal ions, molecular complexes, and II-VI compounds are known to have strong emissions at wavelengths >500 nm. We find that several compounds exhibit emission intensities comparable to commercial phosphors in the 600-900 nm range, including Eu and Sm doped LuPO/sub 4/, ScPO/sub 4/, and YPO/sub 4/. Significant emissions are also observed from Tb, Dy, Er, Pr, and Tm doped phosphates, as well as several intrinsic compounds, notably Hg/sub 2/Cl/sub 2/. Scintillation characteristics of promising compounds (in powdered or small crystal form) are presented.