First-principles study ofCe3+-dopedlanthanum silicate nitride phosphors: Neutral excitation, Stokes shift, and luminescent center identification

Abstract

We study from first principles two lanthanum silicate nitride compounds, LaSi3N5 and La3Si6N11, 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 → 5d neutral excitation of the Ce 3+ ions is simulated through a constrained density-functional theory method coupled with a ∆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 LaSi3N5:Ce and La3Si6N11: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.

Multiple-Valence and Visible to Near-Infrared Photoluminescence of Manganese in ZnGa2O4: A First-Principles Study

“…Some multiplet states can be rationally approximated with the combination of single determinants, which can be derived from the results of the first-principles calculation in the DFT framework. The spin multiplicity control method , supplemented by a constrained occupancy approach , is used for the calculations of excited states. The detailed multiplet setting for multivalent manganese is discussed in Section .…”

First-principles study of the luminescence ofEu2+-doped phosphors

“…Here, β is a parameter related to the shape and size of the anion polyhedron coordinated to the Ce 3+ ion, and R av is the average distance between the Ce 3+ ion and anions in the relaxed structure. Based on D(A) and the energy of the first 4f → 5d transition of Ce 3+ as a free (gaseous) ion, 49340 cm −1 , the transition energy of Ce 3+ ion in compound A can be calculated as: 30,31…”

“…38 Such U term was crucial to obtain the experimentally well-established presence of Eu 4f levels inside the band gap, a defining characteristics of such efficient luminescent materials. 30,39,40 The U value was fixed to 7.5 eV for all fifteen representative Eu 2+ -doped materials, as in our earlier study of two Eu 2+ -doped barium silicate oxynitrides. 39 It was checked that deviation by up to ± 1.0 eV in the U value had little (< 0.1 eV) impact on the transition energies.…”

“…In our recent work, we have studied the luminescence of more than a dozen Ce 3+ -doped phosphors based on first-principles calculations. 30,31 In this context, we have assessed the accuracy of a theoretical methodology to obtain the transition energy and Stokes shift of Ce 3+ -doped phosphors. The method is based on a Constrained Density Functional Theory (CDFT) and ∆SCF analysis of the total energies.…”

Theoretical Calculations Meet Experiment to Explain the Luminescence Properties and the Presence of Defects in m-ZrO2

“…Recent works demonstrated the efficiency of the ∆SCF method (an efficient alternative to TD-DFT) based on the constrained DFT (cDFT) to predict transition energies of Ce 3+ or Eu 2+ doped phosphor compounds. [53][54][55] In these studies, authors applied the so-called constrained DFT methodology (cDFT) as commonly used in molecular simulations. 52 In that context, we embarked on a tentative elucidation of the luminescence properties of Ti doped m-ZrO 2 via DFT calculations.…”