Photoluminescence enhancement study in a Bi-doped Cs₂AgInCl₆ double perovskite by pressure and temperature-dependent self-trapped exciton emission

Abstract

Here, we are reporting a halide precursors acid precipitation method to synthesize Cs2AgIn1–xBixCl6 (x = 0, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, and 1) microcrystals. Cs2AgInCl6 and Bi derivative double...

Cs2AgxNa1−xBiyIn1−yCl6 perovskites approaching photoluminescence quantum yields of 100%

“…The STE state is assumed to form due to a strong coupling of the electronic excitation to lattice vibrations resulting in the localization of the exciton on Bi/Ag halide octahedra and a strong distortion of the octahedral geometry. The self-trapped exciton loses a portion of energy needed for the transition through a potential barrier between free-exciton and STE states as well as lattice reorganization, thus resulting in large Stokes shifts 9,10,17,18,24,25,28,31,32 . The radiative relaxation of the STE state is accompanied by the emission of multiple phonons due to reversal lattice reorganization and, therefore, the PL is emitted as a series of homogeneously and inhomogeneously broadened phonon replicas of the zerophonon band which overlap and form a single symmetrical PL band with a FWHM of many hundred meV 9,10,17,18,24,25,28,32 .…”

“…The self-trapped exciton loses a portion of energy needed for the transition through a potential barrier between free-exciton and STE states as well as lattice reorganization, thus resulting in large Stokes shifts 9,10,17,18,24,25,28,31,32 . The radiative relaxation of the STE state is accompanied by the emission of multiple phonons due to reversal lattice reorganization and, therefore, the PL is emitted as a series of homogeneously and inhomogeneously broadened phonon replicas of the zerophonon band which overlap and form a single symmetrical PL band with a FWHM of many hundred meV 9,10,17,18,24,25,28,32 . The STE PL emission can be very efficient, the PL quantum yield (QY) of a particular CANBIC composition reported to be 86% by Sargent's group 18 and as high as 92% recently by us for CANBICs with 2% Bi content 44 .…”

“…3b, curves 3-10). The development of intense light absorbance and emission upon introduction of minimal amounts of Bi into the CANIC matrix, which otherwise shows a very high energy of the absorption band edge and no PL, are typically interpreted as a result of the Bi species breaking the symmetry of the CANIC lattice and contributing to the formation of CB edge, thus making interband transitions allowed in both directions (light absorption and radiative recombination) 17,18,21,25,26,28,31,32 . In terms of this interpretation, Bi III acts as a "key" opening the inherent capacity of the CANIC matrix for light absorption and emission.…”

“…on the ratios of Ag/Na and Bi/In 17,18,20,21,23,34 . For example, CANBIC compounds often show exceptionally strong dependence of the PL quantum yield (QY) and Huang-Rhys factor on the Ag-to-Na ratio x 18,21,25,[28][29][30]32,34 , while CANBICs with a fixed x typically reveal a dome-shaped dependence of the PL efficiency on the Bi fraction y 17,18,31,32,34,41 . Along with the variable parameters x and y, both Cs and Cl sites can also be varied and potentially substituted by analogs (for example, Cs by Rb or methylammonium).…”

“…At the same time, the potential and capacities of such a search are considerably limited by the current level of development of synthetic approaches to CANBIC perovskites. Typical synthetic protocols are rather unflexible and energy-consuming, requiring the presence of concentrated HCl 8,16,19,21,28,31,32,41,42 or application of prolonged hydrothermal treatments and/or annealings 8,16,18,19,26 . Attempts to make the synthesis of CANBICs and related compounds more environmentally friendly by mimicking syntheses of lead-based halide perovskites, such as antisolvent-or oversaturation-induced crystallization, either yield mixtures of multiple phases with a low control over the crystallization dynamics 16,32,33,43 or do not cover the entire possible ranges of compositions 32,43 .…”