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Preface These elements perplex us in our reaches [sic], baffle us in our speculations, and haunt us in our very dreams. They stretch like an unknown sea before us—mocking, mystifying, and murmuring strange revelations and possibilities. Sir William Crookes (February 16, 1887) Volume 49 of the Handbook on the Physics and Chemistry of Rare Earths adds four chapters to the series, covering subjects as diverse as phosphors for white light-emitting diodes, rare-earth mineralogy and resources, quantum critical matter and phase transitions in rare earths and actinides, and lantha- nide luminescent thermometers. The first chapter (Chapter 278) is devoted to luminescent materials for white light-emitting diodes. The subject is of importance with respect to energy-saving devices. Indeed, despite a sharp increase in the number of lighting devices worldwide, the share of electricity devoted to it is rather decreasing (about 12% presently). This is because of the prominent role played by rare earth phosphors in improving the efficiency of lighting devices, first in compact fluorescent lamps and presently in light-emitting diodes (LEDs). The electricity-to-light conversion efficiency has increased by a factor of 8–9 with respect to the traditional incandescent devices. In this chapter, the authors focus on LEDs based on blue indium gallium nitride chips coated with one or several lanthanide-containing phosphors. Both yellow-emitting trivalent cerium materials and polychromatic phosphors are discussed with respect to the choice of the matrix, of the active components, and of the synthetic methods yielding highly effective and both thermally and photo-stable materials. Rare earth resources are the subject of Chapter 279. A growing number of critical technologies are vitally dependent on rare earth elements, making use of their unique chemical, magnetic, and spectroscopic properties. This has resulted in some of the rare earths, such as Nd, Eu, Tb, and Dy, deemed critical and prompted extensive efforts to find substitutes, which is hard and may not always be possible. Although not that rare in the earth crust, these elements are difficult to produce in the needed quantities because they always occur as intricate mixtures and because the compositions of these mixtures do not match the specific need for given elements. Geopolitical interferences add to the problem. The review provides insight into rare earth ixPDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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