First-principles Study of the Luminescence of Eu2+-doped Phosphors

TL;DR

This study uses first-principles calculations to analyze the luminescence properties of Eu$^{2+}$-doped phosphors, assessing their transition energies, thermal quenching mechanisms, and comparing computational methods.

Contribution

It introduces a validated first-principles methodology for accurately predicting Eu$^{2+}$-doped phosphor luminescence properties and evaluates the thermal quenching mechanisms with detailed energy calculations.

Findings

Calculated absorption and emission energies agree within 0.3 eV of experiments.

The $4f-5d$ crossover is not the main thermal quenching mechanism.

Semi-empirical models are less accurate than first-principles methods.

Abstract

The luminescence of fifteen representative Eu$^{2+}$-doped phosphors used for white-LED and scintillation applications is studied through a Constrained Density Functional Theory. Transition energies and Stokes shift are deduced from differences of total energies between the ground and excited states of the systems, in the absorption and emission geometries. The general applicability of such methodology is first assessed: for this representative set, the calculated absolute error with respect to experiment on absorption and emission energies is within 0.3 eV. This set of compounds covers a wide range of transition energies that extents from 1.7 to 3.5 eV. The information gained from the relaxed geometries and total energies is further used to evaluate the thermal barrier for the $4f-5d$ crossover, the full width at half-maximum of the emission spectrum and the temperature shift of the emission peak, using a one-dimensional configuration-coordinate model. The former results indicate that the $4f-5d$ crossover cannot be the dominant mechanism for the thermal quenching behavior of Eu$^{2+}$-doped phosphors and the latter results are compared to available experimental data and yield a 30$\%$ mean absolute relative error. Finally, a semi-empirical model used previously for Ce$^{3+}$-doped hosts is adapted to Eu$^{2+}$-doped hosts and gives the absorption and emission energies within 0.9 eV of experiment, underperforming compared to the first-principles calculation.