Understanding thermal quenching of photoluminescence from first principles

TL;DR

This paper investigates the thermal quenching mechanisms of Eu-doped phosphors used in white LEDs through first-principles electronic structure analysis, revealing how atomic relaxation and electronic levels influence luminescence efficiency at elevated temperatures.

Contribution

It provides a detailed first-principles analysis of Eu-doped phosphors, identifying the atomic and electronic factors responsible for thermal quenching in WLED applications.

Findings

Eu-5d levels are within the band gap due to electron removal from 4f shell.

Thermal quenching is explained by an auto-ionization model based on energy differences.

Atomic relaxation in excited states is crucial for accurate emission modeling.

Abstract

Understanding the physical mechanisms behind thermal effects in phosphors is crucial for white light-emitting diodes (WLEDs) applications, as thermal quenching of their photoluminescence might render them useless. The two chemically close Eu-doped \Hosta and \Hostb crystals are typical phosphors studied for WLEDs. The first one sustains efficient light emission at 100$^{\circ}$C while the second one emits very little light at that temperature. Herein, we analyze from first principles their electronic structure and atomic geometry, before and after absorption/emission of light. Our results, in which the Eu-5d levels are obtained inside the band gap thanks to the removal of an electron from the 4f$^7$ shell, attributes the above-mentioned experimental difference to an auto-ionization model of the thermal quenching, based on the energy difference between Eu$_{\text{5d}}$ and the conduction band minimum. For both Eu-doped phosphors, we identify the luminescent center, and we show that the atomic relaxation in their excited state is of crucial importance for a realistic description of the emission characteristics.