Comprehensive Band Gap and Electronic Structure Investigations of the Prominent Phosphors M₂Si₅N₈:Eu²⁺ (M = Ca, Sr, Ba) Determined Using Soft X-ray Spectroscopy and Density Functional Theory

Abstract

The suite of LED phosphors M2Si5N8:Eu2+ (M = Ca, Sr, Ba) emerged as indispensable solid-state light sources for the next-generation lighting industry and display systems due to their unique properties. As such, the structure–property relations underpinning their electronic structures are of prime interest. Their band gaps, electronic structures, optical properties, and energy levels are studied with a combination of soft X-ray spectroscopy and density functional theory (DFT) calculations. A clear trend is found where the tunable band gaps range from 3.70 ± 0.20 to 5.00 ± 0.20 eV (when going from Ba to Sr to Ca), following the predictions of the bonding model. The measurements and calculations are also used to derive a systematic trend between the measured band gaps of M2Si5N8 and are confirmed by our density functional theory calculations employing different exchange correlation functionals. These investigations present a comprehensive picture of the M2Si5N8 system, underlining their broad applicability and importance as one of the preeminent phosphors for LED lighting.

Modulating A site compositions of europium(iii)-doped double-perovskite niobate phosphors

“…This means that the small band gap may be more suitable for RE 3+ -activated materials to achieve good PL performance in similar frameworks. 43,44 Therefore, the calculated electrical structures of the prepared phosphors are shown in Fig. 2.…”

Synthesis and Luminescence Properties of Amber Emitting La7Sr[Si10N19O3] : Eu2+ and Syntheses of the Substitutional Variants RE8‐xAEx[Si10N20‐xO2+x] : Eu2+ with RE=La, Ce; AE=Ca, Sr, Ba; 0≤x≤2

“…The valence band maximum is mainly dominated by N and O p ‐states while the conduction band minimum is formed by network forming elements like Si or by elements filling up the network structures such as RE or AE . Going from Ca to Ba d ‐states, the band gap decreases due to the lower energy of Ba d ‐states [17,44,45,52,53] . The determination of the 5 d to conduction band separation by RIXS can be a very useful tool for the distinction whether thermal quenching is an intrinsic material property when the separation is determined to be small or if thermal quenching is extrinsically influenced and can be reduced by optimizing the synthesis [44,45,52] .…”

“…Going from Ca to Ba d-states, the band gap decreases due to the lower energy of Ba d-states. [17,44,45,52,53] The determination of the 5d to conduction band separation by RIXS can be a very useful tool for the distinction whether thermal quenching is an intrinsic material property when the separation is determined to be small or if thermal quenching is extrinsically influenced and can be reduced by optimizing the synthesis. [44,45,52] The influence of thermal ionization and crossover mechanisms compete and depend on the size of the band gap of the host material, whereas the influence of the crossover mechanism increases for lager band gaps (E g > 4 eV).…”

Enhanced effect of co-doping of Ln3+ on the luminescent properties of BaSiO3:Eu3+ red phosphors

“…As one traditional red phosphor, Y 2 O 2 S:Eu 3+ exhibits poor thermal stability [8,9], and it cannot be excited by n-UV light effectively, so new types of phosphor, Mn 4+ , Eu 3+ or Eu 2+ activated different substrates, such as CaMg 2 Al 16 O 27 :Mn 4+ [10], A 2 XF 6 :Mn 4+ [11,12], Ca 3 Y(AlO) 3 (BO 3 ) 4 :Eu 3+ [13], Gd 3 Zn 2 Nb 3 O 14 :Eu 3+ [14], NaSrVO 4 :Eu 3+ , Bi 3+ [15], Na 2 Gd(PO 4 )(MoO 4 ):Eu 3+ [16], Sr(Li 2 Al 2 O 2 N 2 ):Eu 2+ [17,18], M 2 Si 5 N 8 :Eu 2+ [19,20] and MAlSiN 3 :Eu 2+ (M = Ca, Sr, Ba) [21], have been explored. Other than above-mentioned substrates, silicate phosphor has been regarded as a potential candidate for its good chemical and thermal stability, abundant sources and structures [22,23].…”