White light emission with unity efficiency from Cs₂Na_1−xAg_xIn_1−yBi_yCl₆double perovskites: the role of bismuth and silver

Abstract

Double perovskites Cs2Na1-xAgxIn1-yBiyCl6 can emit warm white light with almost unit quantum efficiency and are thus among the most promising materials for solid-state lighting. The emission spectrum is reproducible and...

All Inorganic Sb3+–Ln3+‐Codoped Cs2NaYCl6 for Highly Efficient Single‐Source White‐Light Emission and Ratiometric Optical Thermometer Applications

“…Such a high PLQY value of W2 promotes its application in singlesource WLEDs. [25,[54][55][56] The fabricated WLED based on W2 exhibits white-light emission with the CIE coordinate of (0.28, 0.31) (Figure 5d; Figure S20, Supporting Information). It is worth noting that the WLED based on W2 delivers a R a value of 87, which is much higher than the WLED based on W1 (74.6) due to the better spectral continuity of Sm 3+ .…”

Halide double-perovskites: High efficient light emission and beyond

“…In particular, the comparison between transient absorption (TA) and time-resolved photoluminescence (TRPL) has highlighted the fact that long-lived STEs form independently of Bi doping, but the presence of Bi atoms transforms the STEs from almost completely dark to almost completely bright. 30 The minimum fraction of Bi 3+ sufficient to turn STEs almost completely bright and thus achieve PLQY above 80% was measured to be less than 0.1%. The same ultrafast spectroscopy methods revealed that the presence of Ag is instead crucial to form STEs to begin with.…”

“…29 The low emission quantum yield of the undoped Cs 2 AgInCl 6 has been instead traced back to the parity-forbidden nature of inter-band transitions, related to a high symmetry lattice. The parity-forbidden transition between the valence band maximum (VBM) and the conduction band minimum (CBM) in Cs 2 AgInCl 6 was analyzed by Meng et al using density functional theory with Perdew-Burke-Ernzerhof (DFT-PBE) approach calculations 11 and by Liu et al 30 by ab initio calculations with the Variational Pseudo-Self-Interaction corrected approach (VPSIC). 31 It was demonstrated that both the VBM and CBM lie at the Γ point, giving rise to a direct bandgap of about 2.1 eV and a parity-forbidden transition.…”

“…The emission properties studied by ultrafast spectroscopy demonstrated the presence of excitons trapped in long-lived dark states in the compound and very few bright STEs with nearly 100% radiative efficiency. 30 The homologous compound Cs 2 NaBiCl 6 shows slow conversion to Cs 3 Bi 2 Cl 9 when exposed to air; 12 therefore, the Bi 3+ ion x varied from 0 to 1, has been explored, identifying precisely the transition from direct to indirect bandgap; the transition has been attributed to the band formed by the Bi 6s lone pair. 51,52 In the following paragraphs, it will be discussed how the addition of such new elements helps breaking the parity rules and provides additional emission centers.…”

“…On one hand, the 6s Bi states at the top of the valence band are very likely to increase the oscillator strength for optical emission, much like they do for optical absorption. 30 On the other hand, other effects have been studied, like the role of Bi in passivating defects responsible for non-radiative decay of optical excitation, 29 or its ability to provide localized sites for efficient optical recombination. 56 To further complicate matters, but also rendering them more interesting, the effect of Bi doping on the emission quantum yield is deeply intertwined in the presence of the other monovalent metal cations, namely, Ag and Na.…”