Cascade photon emission in luminophores

Cascade photon emission (CPE), i.e., the production of two or more photons of visible light upon excitation by a single vacuum UV photon, allows for the creation of luminescent materials with the quantum efficiency (Q) greater than unity. Various types of CPE, both experimentally observed and theoretically modeled, are described in this work. The basic characteristics of the matrix and the activator (a rare-earth ion) required for the CPE effect are determined. The most promising CPE materials are the Pr³⁺-activated fluorides with a high coordination number for the activator. It is shown that creation of phosphors with Q > 1, which is currently of great interest from both scientific and technological viewpoints, remains highly problematic.