Basic crystal field theory—A simple and useful tool to understand the structure–property relationship in luminescent materials

Abstract

Crystal field theory has been widely adopted to study the structure–property relationships in luminescent materials. It has the advantage of simplicity and clarity, i.e., the total crystal field splitting is reciprocally proportional to the 5th power of bond length. Yet this rule fails many times, especially in phosphors with low-symmetry sites. In order to provide an intact and practical framework of how to use crystal field theory, we address two main questions in this short review, i.e., how the 5th power rule is produced and why it fails. The regular octahedron potential is selected to show the procedure of crystal field calculations. Then the symmetry limitations on crystal field parameters are discussed considering the contribution from every ligand. After the set up of basic formula, two distinct cases, the reverse garnet effect and neutralization of cationic substitution on peak shifts are selected to show the effectiveness and validity of basic crystal field theory. It is hoped that this work could clarify some misconceptions and help the phosphor researchers in using crystal field theory.