Because fossil fuels are becoming scarce and because of the expected climate change, our standard of living can only be maintained by a significant increase in energy efficiency. Large amounts of energy are consumed for lighting and during operation of displays. Thus, the targets are the development of economical light sources like white-light-emitting diodes and display panels with enhanced efficiency. Solar energy is converted into electricity by solar cells, and their efficiency must be improved considerably. A possible contribution might be delivered by phosphors which allow the conversion of thermal radiation into electrical energy. Although the target of energy efficiency is very important, we must not overlook that medical imaging diagnostic methods require efficient and sensitive detectors. For the solution of these central questions, inorganic solid-state materials doped with rare-earth ions are very promising and are therefore in the focus of current research activities.

Recent Developments in the Field of Inorganic Phosphors

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.

Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

https://www.mdpi.com/1424-8220/9/5/3491/pdf?view=inline

Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

In this review, the major achievements and research and development (R&D) trends from the last decade in the field of single crystal scintillator materials are described. Two material families are included, namely, those of halide and oxide compounds. In most cases, the host crystals are doped with Ce3+, Pr3+ or Eu2+ rare earth ions. Their spin- and parity-allowed 5d–4f transitions enable a rapid scintillation response, on the order of tens to hundreds of nanoseconds. Technological recipes, extended characterization by means of optical and magnetic spectroscopies, and theoretical studies are described. The latter provide further support to experimental results and provide a better understanding of the host electronic band structure, energy levels of specific defects, and the emission centers themselves. Applications in medical imaging and dosimetry, security measures, high-energy physics and the high-tech industry, in which X(γ)-rays or particle beams are used and monitored, are recognized as the main driving factor for R&D activities in this field.

Recent R&D Trends in Inorganic Single-Crystal Scintillator Materials for Radiation Detection

Europium-doped strontium and barium iodide are found to be readily growable by the Bridgman method and to produce high scintillation light yields.

/pdf/strontium-and-barium-iodide-high-light-yield-scintillators-1eaqdwtkwd.pdf

Strontium and barium iodide high light yield scintillators

Effects of Ce Concentration in Scintillation Properties ofLaBr3: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).

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

In this paper, we report on a new cerium doped, high atomic number scintillator, LuI/sub 3/:Ce, for gamma ray spectroscopy. Crystals of this material have been grown using Bridgman process. LuI/sub 3/ crystals doped with 0.5 and 5% Ce/sup 3+/ show high light output (/spl sim/50 000 photons/MeV) and fast principal decay constant (23 to 31 ns). The Ce/sup 3+/ emission peaks at 474 nm. Energy resolution of LuI/sub 3/:Ce coupled to photomultiplier tube (PMT) and measured at 662 keV was /spl sim/11% [full-width at half-maximum (FWHM)]. Timing resolution of LuI/sub 3/-PMT and BaF/sub 2/-PMT detectors operating in coincidence mode was measured to be 210 ps (FWHM). Potential applications of this scintillator are discussed.

LuI/sub 3/:Ce-a new scintillator for gamma ray spectroscopy

Bridgman growth of LaBr3:Ce and LaCl3:Ce crystals for high-resolution gamma-ray spectrometers

We report on cerium doped scintillator - LaBr/sub 3/:Ce for gamma ray spectroscopy. Crystals of this scintillator have been grown using the Bridgman process. This material when doped with cerium has high light output (>60,000 photons/MeV) and fast principal decay constant (<30 ns). The peak of LaBr/sub 3/:Ce emission is at 360 nm. LaBr/sub 3/:Ce shows excellent energy resolution for gamma ray detection. For 662 keV gamma rays (/sup 137/Cs source), energy resolution of 2.7% (FWHM) has been recorded at room temperature for LaBr/sub 3/:Ce crystals coupled to a photomultiplier. This energy resolution is over two times better than that of NaI(TI) scintillators. Analysis of the energy resolution of LaBr/sub 3/:Ce scintillators is presented and the performance of this scintillator at other gamma ray energies is covered. Energy resolution of LaBr/sub 3/:Ce crystals coupled to silicon avalanche photodiodes is discussed. Potential applications of this material are addressed.

P. Wong

Papers

Effects of Ce Concentration in Scintillation Properties ofLaBr3:Ce

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

LuI/sub 3/:Ce-a new scintillator for gamma ray spectroscopy

Bridgman growth of LaBr3:Ce and LaCl3:Ce crystals for high-resolution gamma-ray spectrometers

High energy resolution scintillation spectrometers