The 5d level positions of the trivalent lanthanides in inorganic compounds

Recent research in the field of phosphor and scintillator materials and related detectors is reviewed. After a historical introduction the fundamental issues are explained regarding the interaction of x-ray radiation with a solid state. Crucial parameters and characteristics important for the performance of these materials in applications, including the employed measurement methods, are described. Extended description of the materials currently in use or under intense study is given. Scintillation detector configurations are further briefly overviewed and selected applications are mentioned in more detail to provide an illustration.

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Scintillation detectors for x-rays

The synthesis of lanthanide-activated phosphors is pertinent to many emerging applications, ranging from high-resolution luminescence imaging to next-generation volumetric full-color display. In particular, the optical processes governed by the 4f-5d transitions of divalent and trivalent lanthanides have been the key to enabling precisely tuned color emission. The fundamental importance of lanthanide-activated phosphors for the physical and biomedical sciences has led to rapid development of novel synthetic methodologies and relevant tools that allow for probing the dynamics of energy transfer processes. Here, we review recent progress in developing methods for preparing lanthanide-activated phosphors, especially those featuring 4f-5d optical transitions. Particular attention will be devoted to two widely studied dopants, Ce3+ and Eu2+. The nature of the 4f-5d transition is examined by combining phenomenological theories with quantum mechanical calculations. An emphasis is placed on the correlation of hos...

Lanthanide-Activated Phosphors Based on 4f-5d Optical Transitions: Theoretical and Experimental Aspects.

The light-radiating semiconductor component has a radiation-emitting semiconductor body and a luminescence conversion element. The semiconductor body emits radiation in the ultraviolet, blue and/or green spectral region and the luminescence conversion element converts a portion of the radiation into radiation of a longer wavelength. This makes it possible to produce light-emitting diodes which radiate polychromatic light, in particular white light, with only a single light-emitting semiconductor body. A particularly preferred luminescence conversion dye is YAG:Ce.

Light-radiating semiconductor component with a luminescence conversion element

The scintillation properties of LaBr3 doped with 0.5% Ce3+ are presented. Under optical and gamma ray excitation, Ce3+ emission is observed to peak at 356 and 387 nm. The scintillation light output is 61 000±5000 photons/MeV at 662 keV. More than 90% is emitted with a decay time of 35 ns. An energy resolution (full width at half maximum over the peak position) of 2.85%±0.05% was observed for the 662 keV full absorption peak. A time resolution of 385 ps was obtained using BaF2 as second scintillator and gamma rays of 60Co.

High-energy-resolution scintillator: Ce3+ activated LaBr3

The authors discuss a single-crystal inorganic scintillator, cerium-doped lutetium oxyorthosilicate (Lu/sub 2(1-x)/Ce/sub 2x/(SiO/sub 4/) or LSO). It has a scintillation emission intensity which is approximately 75% of NaI(Tl) with a decay time of approximately 40 ns. The peak emission wavelength is 420 nm. It has a very high gamma-ray detection efficiency due to its density of 7.4 g/cm/sup 3/ and its effective atomic number of 66. Its radiation length of 1.14 cm is only slightly longer than bismuth germanate (BGO). The scintillation properties of Ce-doped LSO are compared to NaI(Tl), BGO, and cerium-doped gadolinium oxyorthosilicate (GSO). In addition to desirable physical properties such as high density and high atomic number, LSO also processes a combination of high emission intensity and fast decay which together are superior to any other known single crystal scintillator. >

Cerium-doped lutetium oxyorthosilicate: a fast, efficient new scintillator

We have discovered a new inorganic single crystal scintillator [1], lutetium oxyorthosilicate doped with cerium, Lu2(SiO4)O:Ce (or “LSO”), which has a unique combination of properties including high emission intensity, fast decay time, high density, and high atomic number. These properties result in excellent signal-to-noise, fast coincidence timing, high count-rate capability, and high detection efficiency making LSO superior to any other known scintillator for many applications. This new scintillator has several important advantages over the scintillator crystals currently used for the detection of gamma rays or X-rays in applications such as medical imaging, nuclear and particle physics, and geophysical exploration. Here we compare the properties of LSO to those of the two most widely used scintillators, namely thallium-doped sodium iodide and bismuth germanate.

A promising new scintillator: cerium-doped lutetium oxyorthosilicate

Gamma-ray and UV-excitation of cerium-doped rare-earth oxyorthosilicates (RE = Y, Gd, and Lu) has been used to investigate the emission mechanism for this family of scintillators. The data clearly indicate the presence of two different luminescence centers, which are attributed to cerium substitution in the two different rare-earth crystallographic sites. While this model explains much of the present and previous UV data, the gamma-ray induced emission from GSO requires a better understanding of the energy transfer between Gd and Ce.

UV and gamma-ray excited luminescence of cerium-doped rare-earth oxyorthosilicates

Two types of excitation and emission spectra with ultraviolet excitation are shown at 11 K for Lu/sub 2/(SiO/sub 4/)O:Ce (LSO) Since there are two crystallographically independent lutetium sites in LSO, the existence of two Ce activation centers (two-activation-center model) is proposed The existence of two different decay time constants of the order of tens of nanoseconds, which are characteristic for fast Ce emission, are shown at 77 K Although the temperature dependence of the decay time and the luminescence efficiency could not be measured for the Ce2, the fact that the gamma-ray-excited emission can be reconstructed from a weighted combination of the Ce1 and Ce2 emission spectra supports the two-activation-center model for LSO >

Jeffrey S. Schweitzer

Papers

Cerium-doped lutetium oxyorthosilicate: a fast, efficient new scintillator

A promising new scintillator: cerium-doped lutetium oxyorthosilicate

UV and gamma-ray excited luminescence of cerium-doped rare-earth oxyorthosilicates

Light emission mechanism of Lu/sub 2/(SiO/sub 4/)O:Ce

Czochralski growth of rare earth oxyorthosilicate single crystals