Emissive Bi-Doped Double Perovskite Cs₂Ag_1–xNa_xInCl₆ Nanocrystals

Abstract

We report the composition-dependent optical properties of Bi-doped Cs 2 Ag 1−x Na x InCl 6 nanocrystals (NCs) having a double perovskite crystal structure. Their photoluminescence (PL) was characterized by a large Stokes shift, and the PL quantum yield increased with the amount of Na up to ∼22% for the Cs 2 Ag 0.4 Na 0.6 InCl 6 stoichiometry. The presence of Bi 3+ dopants was crucial to achieve high PL quantum yields (PLQYs) as nondoped NC systems were not emissive. Density functional theory calculations revealed that the substitution of Ag + with Na + leads to localization of AgCl 6 energy levels above the valence band maximum, whereas doping with Bi 3+ creates BiCl 6 states below the conduction band minimum. As such, the PL emission stems from trapped emission between states localized in the BiCl 6 and AgCl 6 octahedra, respectively. Our findings indicated that both the partial replacement of Ag + with Na + ions and doping with Bi 3+ cations are essential in order to optimize the PL emission of these systems.

Lead‐Free Sodium–Indium Double Perovskite Nanocrystals through Doping Silver Cations for Bright Yellow Emission

“…Thehighest PLQE of Cs 2 NaInCl 6 :10 %AgNCs is up to 31.1 %( Figure S19), much higher than the PLQE of reported lead-free DP NCs. [20][21][22][23][26][27][28] Thea bove phenomena show that the dark STEs state of Cs 2 NaInCl 6 NCs exists and is broken by doping Ag + .Thus,the property of dark STEs state of Cs 2 NaInCl 6 NCs can be analogized by the property of bright STEs state of Ag-doped NCs (details in Figure S20). Thephysical origin of this transition from dark STEs state to bright STEs state have two reasons.Firstly,The interaction of NaCl 6 and AgCl 6 octahedra can break the parity-forbidden transition leading to effective PL emission.…”

“…[11,12] Unfortunately,t he Sn 2+ and Ge 2+ ions are extremely instable and oxidized easily to Sn 4+ and Ge 4+ ,r espectively.H eterovalent substitution can form lead-free perovskites NCs:f irstly,s ubstituting three Pb 2+ cations with two trivalent B 3+ cations A 3 B 2 X 9 (A = Cs,R b; B = Sb,B i) ; [13][14][15][16] secondly,s ubstituting two Pb 2+ cations with aq uadrivalent B 4+ cation Cs 2 BX 6 (B = Sn, Pd); [17,18] thirdly, substituting two Pb 2+ cations with am onovalent B + and at rivalent B' 3+ cations Cs 2 BB'X 6 (B = Ag, Na;B ' = Bi, Sb, In). [19][20][21][22][23] However, the electronic dimensionality of A 3 B 2 X 9 and Cs 2 BX 6 NCs can be reduced, lead to decreasing carrier mobility. [21,24,25] Thel ead-free double perovskite (DP) NCs have potential to be excellent photoelectric materials due to 3D structure,non-toxicity and stability.…”

“…1.6 %). [22] Thei mprovement of photoluminescence (PL) properties by multivalent cation (Mn 2+ or Bi 3+ )d oping has been widely concerned, [22,23,26] but the mechanism of little PL emission is still unclear in direct band gap DP NCs.T oo ur knowledge,t hus far,t here is no report about all-inorganic Cs 2 NaInCl 6 DP NCs.…”

“…Although Cs 2 AgInCl 6 NCs have been synthesized by using other constant temperature synthetic routes (optimizing precursor type), the morphology of these NCs is not very regular and they have phase separation (there are lots of black spots in TEM images). [22,23,[26][27][28] Thev ariable temper-ature hot injection is superior to conventional hot injection for In-based DP NCs synthesis,and suitable for the synthesis of other lead-free perovskites NCs ( Figure S1-S10 in the Supporting Information). TheC s 2 NaInCl 6 NCs are synthesized by variable temperature one-pot hot injection.…”

Tunable Color Temperatures and Efficient White Emission from Cs2Ag1−xNaxIn1−yBiyCl6 Double Perovskite Nanocrystals

“…Manna and co‐workers reported the Bi‐doped Cs 2 Ag 0.4 Na 0.6 InCl 6 NCs with a PLQY of ≈22%. Their Cs 2 Ag 1− x Na x InCl 6 NCs showed a fixed emission when the amount of Na evolved from 0% to 100% . Such quantum yield and limited emission spectra impede their competitiveness for single‐emitter‐based white light‐emitting applications .…”