Broadband White Emission in Cs2AgIn1-xBixCl6 Phosphors

The photoluminescent properties of the lead-free double perovskite solid solution Cs2AgIn1-xBixCl6 have been investigated. The In3+ end member, Cs2AgInCl6, is a direct gap semiconductor that absorbs UV light (lambda < 350 nm) and shows little to no photoluminescence. Incorporation of Bi3+ leads to a strong sub-band gap absorption that peaks in the near UV (similar to 360 nm) and extends into the visible. This absorption, which is thought to originate from localized 6s(2) -> 6s(1)p(1) transitions on Bi3+ ions, is split by a Jahn-Teller distortion of the excited state. In-rich samples show strong photoluminescence that is attributed to radiative decay of self-trapped excitons, with a broad emission peak of significant intensity from 450 to 750 nm. The color of the emitted light is best described as yellow-white (lambda(max )approximate to 625 nm), due to the extreme breadth of the emission peak (fwhm approximate to 217(2) nm). The excitation spectrum extends out to 450 nm for samples near x = 0.25, while the photoluminescent quantum yield (PLQY) reaches a maximum of 39 +/- 3% in the x = 0.167 sample. The emission characteristics, which include a correlated color temperature (CCT) of 3119 K and a color rendering index (CRI) of 85, coupled with an excitation spectrum that can be driven by visible photons emitted from a Ga1-xInxN LED, make Cs2AgIn1-xBixCl6 phosphors promising for use in solid state white lighting applications.