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 (λ < 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 (∼360 nm) and extends into the visible. This absorption, which is thought to originate from localized 6s2 → 6s1p1 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 (λmax ≈ 625 nm), due to the extreme breadth of the emission peak (fwhm ≈ 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.