Enhanced thermal quenching characteristic via carbon doping in red‐emitting CaAlSiN₃:Eu²⁺ phosphors

Abstract

Enhancing thermal quenching characteristic of phosphor for use in high power white‐light‐emitting diodes (wLEDs) is a significant materials challenge. To achieve this goal, a series of red‐emitting carbidonitride phosphors Ca0.992AlSiN3 − 4/3xCx:0.008Eu2+ have been synthesized by high‐temperature solid‐state reaction method. Crystal structure, luminescence properties, and thermal quenching process are investigated. The location of carbon in the lattice is proved by the Raman spectra. The preferential crystallographic site of carbon is validated by the first‐principles density functional theory calculations combining the Rietveld refinement. With carbon doping from x = 0 to x = 0.24, the emission spectra are blue‐shifted from 656.8 to 650.2 nm, and the fitted lifetime of Eu2+ decreases from 775.3 to 721.7 ns. Replacing nitrogen by carbon enhances thermal quenching characteristic by 8.9% at 300°C. Carbon doping enlarges the thermal ionization energy barriers (EdC) which is calculated at great length, and suppresses thermal ionization process. A wLED fabricated by the combination of a blue chip with the as‐synthesized red phosphor and LuAG: Ce3+ green phosphor shows a high color rendering indexes (Ra = 95.9 and R9 = 92). The promising application of Ca0.992AlSiN3 − 4/3xCx:0.008Eu2+ phosphor for wLEDs is proved by all results above.

Enhanced thermal stability of CaAlSiN3:Eu2+ phosphors by superficial carbon modification

“…As shown in the inset in Figure 4, the peak emission positions show a blue shift from 662 to 658 nm as the addition of nano carbon powder increases. Based on previous studies, 11 the substitution of C for N in the CASN:Eu 2+ lattice leads to the blue‐shifted emission, which is attributed it to the weaker CFS of the activator 39 . Hence, the blue shift after the thermal post‐treatments can further indicate the incorporation of C into the lattice of the surface.…”

“…It indicates that there are still a little amount of carbon on the surface, even though nano carbon powder cannot be directly observed after the thermal post‐treatments. It has been reported that carbon atoms preferentially substitute for nitrogen atoms in CaAlSiN 3 lattice 11,31 . As known, the N atoms directly linked with the Ca, Al and Si atoms in CaAlSiN 3 lattice 32 .…”

“…It has been reported that carbon atoms preferentially substitute for nitrogen atoms in CaAlSiN 3 lattice. 11,31 As known, the N atoms directly linked with the Ca, Al and Si atoms in CaAlSiN 3 lattice. 32 To characterize the introduction of C in the surface of CASN:Eu 2+ crystal, the XPS spectra of samples for (a) Al 2p, (b) Si 2p, and (c) Ca 2p are investigated, as shown in Figure 3.…”

“…Li et al synthesized a series of rare‐earth doped Ca 1‐x Al 1‐x Si 1+x N 3‐x O x samples with the inspiration of the solid solution strategy, and the thermal quenching temperature of CASN:Eu 2+ was raised up by substituting Al and N atoms with Si and O atoms 10 . Tian et al introduced carbon into the lattice of CASN:Eu 2+ to form carbidonitride phosphor, and the thermal quenching characteristic was enhanced, owing to the enlargement of thermal ionization energy barriers caused by carbon doping 11 . The chemical substitution of host lattice could affect the thermal properties due to changes on the location environment of Eu 2+ ion.…”

“…10 Tian et al introduced carbon into the lattice of CASN:Eu 2+ to form carbidonitride phosphor, and the thermal quenching characteristic was enhanced, owing to the enlargement of thermal ionization energy barriers caused by carbon doping. 11 The chemical substitution of host lattice could affect the thermal properties due to changes on the location environment of Eu 2+ ion.…”