Cerium-doped LaSi3N5: Computed electronic structure and band gaps

Ibrahim, I. I.; Lenčéš, Zoltán; Benco, Ľ.; Hrabalová, Monika; Šajgalı́k, Pavol

doi:10.1016/j.jeurceramsoc.2013.12.054

Cited by 12 publications

(14 citation statements)

References 28 publications

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“…19 In the present study, Ce 3+ ions are directly excited from a 370 nm excitation wavelength what is consistent with previous studies. For example, for Ce-doped phosphor, the PLE peak was centered at 357 nm and its FWHM was ~75 nm, 32 while for Ce-doped SiO 1.5 , a similar matrix to the one studied here, a PLE peak was centered at 300 nm with a FWHM of almost 50 nm. 19 Moreover, an important Stokes shift of 97 nm (5600 cm -1 ) was found, which is similar to the one observed in Ce 3+ ion doped inorganic matrices.…”

Section: Photoluminescence and Photoluminescence Excitation Spectroscopysupporting

confidence: 65%

The nitrogen concentration effect on Ce doped SiO_xN_y emission: towards optimized Ce³⁺ for LED applications

et al. 2018

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Ce-doped SiO x N y films are deposited by magnetron reactive sputtering from a CeO 2 target under nitrogen reactive gas atmosphere. Visible photoluminescence measurements regarding the nitrogen gas flow reveal a large emission band centered at 450 nm for a sample deposited under a 2 sccm flow. A special attention is paid to the origin of such an emission at high nitrogen concentration. Different emitting centers are suggested in Ce doped SiO x N y films (e.g. band tails, CeO 2 , Ce clusters, Ce 3+ ions), with different activation scenarios to explain the luminescence. X-ray photoelectron spectroscopy (XPS) reveals the exclusive presence of Ce 3+ ions whatever the nitrogen or Ce concentrations, while transmission electron microscopy (TEM) shows no clusters or silicates upon high temperature annealing. With the help of photoluminescence excitation spectroscopy (PLE), a wide excitation range from 250 nm up to 400 nm is revealed and various excitations of Ce 3+ ions are proposed involving direct or indirect mechanisms. Nitrogen concentration plays an important role on Ce 3+ emission by modifying Ce surroundings, reducing the Si phase volume in SiO x N y and causing a nephelauxetic effect. Taking into account the optimized nitrogen growth parameters, the Ce concentration is analyzed as new parameter. Under UV excitation, a strong emission is visible to the naked eye with high Ce 3+ concentration (6 at. %). No saturation of the photoluminescence intensity is observed, confirming again the lack of Ce cluster or silicate phase formation due do the nitrogen presence.

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Section: Photoluminescence and Photoluminescence Excitation Spectroscopysupporting

confidence: 65%

The nitrogen concentration effect on Ce doped SiO_xN_y emission: towards optimized Ce³⁺ for LED applications

et al. 2018

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“…If we compare the band gaps of LaSi 3 N 5 doped with Eu and Ce with the gap of Sm‐doped phosphor the calculated values indicate that with increasing number of f electrons (1 in Ce 3+ → 5 in Sm 3+ ) the position of the f band is continuously shifted from the top of the p band toward the bottom of the CB and causes the continuous decrease in the band gap (Ce 4.65 eV → Sm 2.01 eV). However, this is valid only for a series of configurations exhibiting the same bonding scheme.…”

Section: Resultsmentioning

confidence: 99%

“…[7][8][9][10][11][12][13][14][15][16][17] Except of these two well-established dopants also samarium activated nitride compounds are studied. 18 In our previous work europium-and cerium-doped LaSi 3 N 5 phosphors were synthesized from LaSi/Si/Si 3 N 4 / Eu 2 O 3 and LaSi/Si/Si 3 N 4 /CeO 2 mixtures by direct nitridation at 1390°C and additional annealing at 1630°C for 3 h. 14,19 We have also carried out ab initio density-functional theory (DFT) calculations of the electronic structures and band gaps of stoichiometric LaSi 3 N 5 and Eu and Ce-doped LaSi 3 N 5.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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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.

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“…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.…”

Section: Introductionmentioning

confidence: 99%

“…Low concentration of the RE cation in the LaSi 3 N 5 host lattice (1 -6%) required the use of a large supercell. Because the size of the supercell prohibited the use of computationally demanding many-body GW method, we used the hybrid functional HSE06 to localize 4f states in Eu- [27], Ce- [28], and Sm-doped [29] LaSi 3 N 5 host lattice. Our model doping considered both RE 3+ and RE 2+ cations.…”

Section: Introductionmentioning

confidence: 99%

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

Ibrahim

Lenčéš

Šajgalı́k

et al. 2015

Journal of Luminescence

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First principles calculations of rare earth (RE)-doped LaSi 3 N 5 host lattice are performed to obtain the electronic structure, the band gap (BG), and the character of electronic transitions.Doping with both trivalent and bivalent RE cations is inspected. RE 4f states form two bands of occupied and unoccupied states separated by ~5 eV. In RE 3+ -doped compounds 4f states are shifted by ~6 eV to more negative energies compared with RE 2+ -compounds. This stabilization causes that RE 3+ 4f bands are in a different position relative to the valence band and the conduction band than RE 2+ 4f bands and therefore different electronic transitions apply. BG of RE 3+ -compounds decreases from ~4.6 eV (Ce) to ~0.5 eV (Eu). Except for Ce 3+ , exhibiting the 4f→5d transition, other RE 3+ -compounds show the charge transfer of the p → 4f character. BG of RE 2+ -compounds increases from ~0.80 eV (Ce, Pr) to ~0.95 eV (Nd, Pm), ~1.43 eV (Sm), and ~3.28 eV (Eu) and the electronic transition is of the 4f→5d character. The energy level scheme constructed from ab initio calculated electronic structures agrees well with the experimental energy level diagram. The agreement demonstrates the reliability of the hybrid functional HSE06 to describe correctly bands of nonbonding RE 4f electrons. Keywords:4f states in lanthanides, LaSi3N5 host lattice, ab initio calculation, 4f energy level scheme, band gaps Pm, Sm, Eu, Gd, Tb, Dy, Ho) in good agreement with experiments. Another way to improve the standard DFT is to modify the intra-atomic Coulomb interaction through the LDA+U approach [13][14][15]. It was shown that this approach allowed for a correct treatment of electronic states in Ce 2 O 3 [16] and in CeO 2 [17]. The physical idea behind LDA+U or GGA+U scheme comes from Hubbard Hamiltonian. In the practical implementations, the onsite two-electron integrals are expressed in terms of two parameters. These are the Hubbard

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Cerium-doped LaSi3N5: Computed electronic structure and band gaps

Cited by 12 publications

References 28 publications

The nitrogen concentration effect on Ce doped SiO_xN_y emission: towards optimized Ce³⁺ for LED applications

The nitrogen concentration effect on Ce doped SiO_xN_y emission: towards optimized Ce³⁺ for LED applications

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

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

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Cerium-doped LaSi3N5: Computed electronic structure and band gaps

Cited by 12 publications

References 28 publications

The nitrogen concentration effect on Ce doped SiOxNy emission: towards optimized Ce3+ for LED applications

The nitrogen concentration effect on Ce doped SiOxNy emission: towards optimized Ce3+ for LED applications

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

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

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The nitrogen concentration effect on Ce doped SiO_xN_y emission: towards optimized Ce³⁺ for LED applications

The nitrogen concentration effect on Ce doped SiO_xN_y emission: towards optimized Ce³⁺ for LED applications

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