Structure and photoluminescence of(Ca,Eu)2SiS4 powders

Abstract

The photoluminescence of Ca2SiS4:Eu powders was investigated in detail as a function of europiumconcentration (from 0.1% Ca substitution to the fully substitutedEu2SiS4). At low europiumdopant concentration (<10%) the powders crystallize in an orthorhombic structure and the emission spectrum is dominatedby two broad emission bands, at 564 and 660 nm. The emission can be tuned from yellow (CIEx = 0.46,y = 0.53) to red(CIE x = 0.65,y = 0.35) by variation of the Eu concentration. An energetic coupling exists between both bands,leading to a broad excitation wavelength range. Powders with high europium concentration(>40%) crystallize in a monoclinic structure, details of which were determinedby Rietveld refinement of x-ray diffraction data. For the compositionCaEuSiS4 (i.e. 50% substitution), the luminescence peaks at 614 nm, shifting to shorterwavelengths upon further substitution of Ca by Eu. Although considerable thermalquenching is present at room temperature in the fully Eu-substituted compound,Eu2SiS4 is still photoluminescent, with a peak emission wavelength of 577 nm. A strongcorrelation is found between the crystallographic and luminescent properties of the(Ca,Eu)2SiS4 powders. The broad emission and excitation bands make this phosphor a good candidatefor use in phosphor-converted light-emitting diodes (pcLEDs).