First-principles study of Ce$^{3+}$ doped lanthanum silicate nitride phosphors: Neutral excitation, Stokes shift, and luminescent center identification

TL;DR

This study uses first-principles calculations to analyze Ce$^{3+}$ doped lanthanum silicate nitride phosphors, identifying luminescent centers and explaining their emission color differences through electronic structure and excitation analysis.

Contribution

It introduces a first-principles approach combining constrained DFT and ${ m riangle}$SCF to characterize excitation, emission, and luminescent centers in doped phosphors.

Findings

Identified luminescent centers in LaSi$_{3}$N$_{5}$:Ce and La$_{3}$Si$_{6}$N$_{11}$:Ce.

Achieved agreement with experimental emission energies and Stokes shifts within 20%.

Explained the different emission colors based on electronic structure analysis.

Abstract

We study from first principles two lanthanum silicate nitride compounds, LaSi$_{3}$N$_{5}$ and La$_{3}$Si$_{6}$N$_{11}$, pristine as well as doped with Ce$^{3+}$ ion, in view of explaining their different emission color, and characterising the luminescent center. The electronic structures of the two undoped hosts are similar, and do not give a hint to quantitatively describe such difference. The $4f\rightarrow 5d$ neutral excitation of the Ce$^{3+}$ ions is simulated through a constrained density-functional theory method coupled with a ${\Delta}$SCF analysis of total energies, yielding absorption energies. Afterwards, atomic positions in the excited state are relaxed, yielding the emission energies and Stokes shifts. Based on these results, the luminescent centers in LaSi$_{3}$N$_{5}$:Ce and La$_{3}$Si$_{6}$N$_{11}$:Ce are identified. The agreement with the experimental data for the computed quantities is quite reasonable and explains the different color of the emitted light. Also, the Stokes shifts are obtained within 20\% difference relative to experimental data.