Lead-free double
cation metal halide perovskites have recently
attracted considerable attention, with continuing research efforts
focusing on the improvement of their stability and photoluminescence
quantum yield (PL QY). In this study, Ce3+ has been co-doped
together with Bi3+ into lead-free double perovskite Cs2AgInCl6 nanocrystals (NCs) in order to improve
their crystallinity and PL QY. Both uncoordinated chloride ions and
silver vacancies could be eliminated using this co-doping strategy,
and the resulting Ce3+,Bi3+-co-doped Cs2AgInCl6 NCs showed adjustable PL emission peaks
in the range of 589 to 577 nm by varying the doping amount of Ce3+ with a fixed feeding ratio of bismuth precursor set at 1%.
Cs2AgInCl6 NCs doped with 1% Bi alone reached
a PL QY of 10% for the PL peak centered at 591 nm, while those co-doped
with 1% Bi and 2% Ce together achieved the highest PL QY of 26% for
the PL peak centered at 580 nm. The use of Ce3+ as a dopant
promoted the localization of self-trapped excitons to prevent PL quenching,
although the ion’s 5d excited state may potentially provide
an energetically favorable indirect route for the radiative relaxation
process. This also resulted in a blue shift of the PL maximum and
increased the exciton binding energy, thus promoting the radiative
recombination of self-trapped excitons.
Lead-free two-dimensional metal halide perovskites have recently emerged as promising light-emitting materials due to their improved stability and attractive optical properties. Herein, a facile room temperature wet milling method has been developed to make Dion–Jacobson (DJ) phase ODASnBr4 perovskite microcrystals, whose crystallization was accomplished via the aid of introduced primary alcohols: ethanol, butanol, pentanol, and hexanol. Due to the strong intermolecular hydrogen bonding, the use of ethanol promoted the formation of non-doped ODASnBr4 microcrystals, with an emission peaked at 599 nm and a high photoluminescence quantum yield (PL QY) of 81%. By introducing other primary alcohols with weaker intermolecular hydrogen bonding such as butanol, pentanol, and hexanol, [SnBr6]4− octahedral slabs of the DJ perovskite microcrystals experienced various degrees of expansion while forming O–H…Br hydrogen bonds. This resulted in the emission spectra of these alcohol-doped microcrystals to be adjusted in the range from 572 to 601 nm, while keeping the PL QY high, at around 89%. Our synthetic strategy provides a viable pathway towards strongly emitting lead-free DJ perovskite microcrystals with an improved stability.
We developed a facile approach to fabricate highly luminescent and stable quasi-2D/3D (ODA) 2 FA n−1 Pb n Br 3n+1 /FAPbBr 3 (ODA: octadecylammonium; FA: formamidinium) perovskite films. Trace amounts of octadecylamine dissolved in toluene used as an antisolvent were partially protonated by FAPbBr 3 and interacted with [PbBr 6 ] 4− octahedral layers, forming quasi-2D perovskites. Moreover, octadecylamine uniformly and densely covered the perovskite surface rendering it hydrophobic and prevented penetration of water, making these perovskite films stable and strongly luminescent in water for several tens of minutes without any encapsulation. Adjusting the concentration of octadecylamine, we were able to produce perovskite films with an exceptionally high photoluminescence quantum yield (PL QY) of 91%, which was ascribed to the efficient energy funneling from the 2D to the 3D perovskite phase and the passivation action of the organic additive.
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