Band 240, Heft 7-8

Inorganic, radiation-converting materials, commonly referred to as phosphors, luminescent materials, or luminophores, present an important class of functional materials used in a broad-range from everyday consumer appliances to highly specialized technical equipment. The properties of such materials are often the product of an intimate relationship between an activator ion and the host structure. This review briefly summarizes the photo physics of luminescent centres, with a focus on lanthanide ions and their structure-property relations. It then delves into various lighting technologies that utilize conversion materials. In this framework key developments in phosphor research during the 20th century, ultimately resulting in highly mature applications such as plasma display panels (PDPs) and fluorescent tubes, are highlighted. Key performance parameters for these technologies are discussed, with a focus on how the ongoing dismantling of the structure-property relationship led to the optimization of these phosphors. This review also highlights phosphors for light emitting diodes (LEDs) that are used to enable so called phosphor converted LEDs (pcLEDs), which represent the current and potential ultimate light source for general lighting and many display technologies. The severe requirements on LED phosphors are analysed, emphasizing classes such as cerium-activated garnets and europium-activated nitrides. Their luminescent and structural properties are explored in detail. Building on established structure-property principles for common LED phosphors, the review examines how these guidelines can inspire the development of next-generation phosphor materials. Finally, the optimization of key phosphor properties, including emission colour (point), thermal quenching temperature ( T 1/2 ), and full width at half maximum ( fwhm ) are discussed. This review concludes by outlining some future trends and directions in phosphor development.

The development of superstructures derived from simple crystal structures under equilibrium conditions provides valuable information about the energetics of the atomic interactions. Moreover, collective deformation processes of superstructures as in martensitic transformations or during twinning can retain atomic correspondences leading also to non-equilibrium superstructures. Against this background, the exhaustively enumerated superstructures of the body-centered cubic structure (bcc) and of the cubic close packed structure (fcc) up to 4 atoms per primitive unit cell were analysed in view of their behavior upon the Bain deformation and Σ3 (pseudo)twinning processes. It turns out that the enumerated superstructures form various closed sets which are intertransformable in these ways. This fact can be attributed to the mathematical characteristics of the enumeration process. The consequences of these types of intertransformation processes between prominent and less prominent bcc and fcc superstructures having in reality different energies are discussed in view of the effect of ordering on martensitic transformations.