Correlating long-range order and local structure to the properties of inorganic solids.

摘要

Relating the structures and compositions of inorganic materials to their function is at the core of rational design of new materials. Dopant ions are responsible for function in many inorganic materials, such as zeolites for catalysis, phosphor materials, semiconductors, solar materials, and thermoelectrics. Understanding the distribution, local structure, and local compositions around dopant ions is crucial for rational design of new and improved materials. Here, the focus will be on phosphor materials, but the methodology is applicable to the other materials mentioned.;The advent of bright-blue LEDs in the mid-1990s following the developmentby Nakamura and others of (In,Ga)N devices was a landmark achievement in solid state lighting. The availability of bright radiation at the high-energy end of the visible spectrum provided a simple and cost-effective means of generating white light by the process of using phosphors to partially down-convert some of the blue emission to longer wavelengths corresponding to colors such as green, yellow, and red. This results in lighting devices that offer greater efficiency, significantly longer working lives, and a complete absence of toxic elements in their constituent parts.;Phosphor compounds are an integral part of the white solid-state lighting design, since currently no efficient green and yellow LEDs exist. Although many phosphor compounds have been discovered and used in the past, they have been discovered empirically using basic solid-state chemistry intuition. New phosphors with greater amounts of red emission and high quantum efficiencies up to 500 K are highly sought after, yet no rational design rules for finding new phosphors have been proposed. Here, the structure-composition-property relations of many phosphor compounds are investigated, including the well-known phosphor Y3-xCexAl 5O12 (YAG:Ce3+), a new nitride phosphor La 3-xCexSi 6N11 (LSN:Ce3+), the phosphor Ca1- xCexSc2O4 (CSO:Ce3+), and the oxyfluoride solid-solution phosphor Sr 2:975Ce0:025Al1-xSi xO4+xF1- x (SASF:Ce3+). Using a combination of powerful experimental methods, the structural properties of these phosphors, including the nature of the Ce3+ local environments, are determined and are correlated with the macroscopic luminescent properties of the Ce-substituted phosphors. From this, design rules for rational discovery of new phosphors are presented.