Sm‐Doped LaSi₃N₅: Synthesis, Computed Electronic Structure, and Band Gaps

Abstract

LaSi3N5‐based phosphor doped with Sm was prepared by the nitridation of LaSi‐Si‐Si3N4‐Sm2O3 powder mixture. The emission spectrum shows two main bands with maxima at 595 nm in the orange region and at ~650 nm in the red region. The excitation spectrum of Sm‐doped LaSi3N5 shows a maxima at 585, 570, and 405 nm. First‐principles density‐functional theory calculations were performed using Vienna ab initio simulation package to enhance the understanding of the electronic structure of the stoichiometric LaSi3N5 and Sm‐doped LaSi3N5. The electronic structure and band gaps were calculated in 2 × 1 × 2 supercell with 144 atoms using the more precise screened Coulomb hybrid functional HSE06. Both La3+/Sm3+ and La3+/Sm2+ substitutions were calculated. The calculated band gap of Sm(III)‐doped LaSi3N5 is 2.01 eV, in reasonable agreement with the experimental value of 2.12 eV, but corresponds to the unrealistic transition between the N, Si p states, and unoccupied Sm 4f states. The band gap of 1.43 eV calculated for Sm(II)‐doped LaSi3N5 is smaller than the available experimental value, but corresponds to the correct transition between nonbonding Sm 4f states and empty La 5d states. Optical properties are found to be governed by f electrons of the Sm(II) dopant.

Electronic structure and energy level schemes of RE3+:LaSi3N5 and RE2+:LaSi3N5−xOx phosphors (RE=Ce, Pr, ND, Pm, Sm, Eu) from first principles

“…Experimental excitation energy of Sm-doped LaSi 3 N 5 of 2.12 eV [29] fits the line of the RE 3+ doping (Fig. 6).…”

“…We present the electronic structure of a series of RE-doped LaSi 3 N 5 host lattice (RE= Ce, Pr, Nd, Pm, Sm, Eu). Following our recent work on synthesis, optical properties and model calculations of the LaSi3N5 host lattice doped with Eu [27], Ce [28] and Sm [29] in this work we perform calculations on Pr-, Nd-, and Pm-doped LaSi 3 N 5 to complete the whole series of doped materials, in which the occupation of 4f energy level continuously increases from 4f 0 to 4f 7 . In calculations the same model structure and same models of doping are used as in previous works [27][28][29] to simulate the doping with trivalent and bivalent RE cations.…”

“…In our recent papers we have presented the experimental excitation and emission spectra of LaSi 3 N 5 :RE (RE = Eu, Ce, Sm) phosphors [27][28][29]. In the computational part of these papers we focused on the location of the band of 4f states between the VB and the CB.…”

“…Results on three RE-doped materials (RE = Eu, Ce, Sm) [27][28][29] show that the position of the 4f band changes with both atomic number and the oxidation state of the RE cation. In [27][28][29] we have shown that the formation of vacancies makes only negligible influence of the band gap of the system. In the present work the formation of vacancies is therefore not considered.…”

Influence of N Doping on the Electronic Structure and Absorption Spectrum of Ca$lt;inf$gt;2$lt;/inf$gt;SiO$lt;inf$gt;4$lt;/inf$gt;: Eu$lt;sup$gt;2+$lt;/sup$gt; Phosphor

“…4(b) that at the Fermi level, N2p orbits and Eu4f orbits overlap each other. The little stabilized electrons at the Fermi level are N2p electrons [17] . Therefore, the energy electron transition is the valence band charges transfer of the nonbonding electron from N2p to the empty band of Eu4f states.…”