High partial thermal conductivity of luminescence sites: a crucial factor for reducing the heat-induced lowering of the luminescence efficiency

Abstract

The good thermal stability of a phosphor is crucial for its practical applications. Unfortunately, in the past decades, only the Gurney–Mott equation was available to describe the relation between the luminescence properties of a phosphor and temperature, which is, however, phenomenological and not precise. In this work, we introduced a hypothesis that the lowering of the luminescence efficiency of a phosphor is caused by the heat generated during the luminescence process and can be reduced if the luminescence site dissipates the heat away. We verified this hypothesis by evaluating the thermal conductivities κ of their luminescence sites, the Eu atoms, in the three phosphors, SrLiAl₃N₄:Eu²⁺, Sr₂Si₅N₈:Eu²⁺ and SrSiN₂:Eu²⁺, as well as those of the Sr atoms in their hosts SrLiAl₃N₄, Sr₂Si₅N₈ and SrSiN₂. It is suggested that our new approach can be employed as a practical criterion to search for phosphor materials with efficient luminescence properties.