Enhancing Mn Emission of CsPbCl₃ Perovskite Nanocrystals via Incorporation of Rubidium Ions

Highlights

• Mn doped CsPbCl₃ perovskite NCs with incorporation of Rb ions were synthesized.

• The photoluminescence quantum yields of Mn doped CsPbCl₃ NCs with Rb doping reached up to 63.18%.

• The enhanced Mn photoluminescence was observed in Mn doped CsPbCl₃ NCs at 80 K after Rb incorporation.

• The emission enhancement is related to reduction of defects through Rb ion doping.

Abstract

Mn doped cesium lead halide perovskite nanocrystals (NCs) have potential application for white light emitting diodes. However, the emission of doped NCs is limited to trap-mediated energy transfer. The Mn doped CsPbCl₃ NCs with corporation of rubidium (Rb⁺) ions (Mn:Cs_1-xRb_xPbCl₃ NCs, x = 0, 0.1, 0.2, 0.3, and 0.4) were synthesized. The effect of the optical and structural properties of Mn:Cs_1-xRb_xPbCl₃ NCs were studied by steady-state and time-resolved photoluminescence spectroscopy. The photoluminescence quantum yields and lifetimes of Mn doped CsPbCl₃ NCs with different Rb⁺ contents were obtained. It was found that the Mn doped CsPbCl₃ NCs with Rb⁺ content of 0.1 exhibited the highest Mn²⁺ emission quantum yield up to 63.18%. Interestingly, the temperature-dependent PL spectra demonstrated the enhanced Mn²⁺ emission of Mn doped CsPbCl₃ NCs at low temperature of 80 K. The experimental result indicated the Mn²⁺ emission of Mn doped CsPbCl₃ NCs was enhanced by incorporating Rb⁺ ions.

Introduction

All-inorganic metal halide perovskite CsPbX₃ (X = Cl, Br, I) nanocrystals (NCs) due to high fluorescence quantum efficiency, the tunable emission wavelength and low-cost solution processing have exhibited wide applications in solar cells, photodetectors, light emitting diodes (LEDs), and so on [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]]. The chemical formula of typical perovskites is ABX₃, A is a monovalent cation [A = CH₃NH₃ (MA), CH₃(NH₂)₂ (FA), or Cs⁺], B is a divalent cation [B = Pb²⁺, Sn²⁺, Ni²⁺, or Cd²⁺], X is a halide (X = Cl-, Br- or I-). Substitution of A- and B-site cations can further optimize the crystal quality and phase stability of the perovskite [[12], [13], [14], [15], [16]], meanwhile, the band gap remains basically unchanged. Saliba et al. incorporated Rb⁺ (A-site substitution) into CsFAMAPbI₃ perovskite solar cells, which not only achieved a stable efficiency of up to 21 %, but also maintained 95 % of the initial performance at 85 °C for 500 h [17]. Amgar et al. improved the photoluminescence quantum yield (PL QY) and stability of perovskite NCs by doping cationic Rb⁺ ions, which was attributed to the change in NCs size and crystallinity as well as the decrease of defects as nonradiative recombination centers [18]. Some experimental results about enhanced PL QYs of perovskite NCs via A-site doping have been reported [[19], [20], [21]]. On the other hand, some metal cations for B-site substitution are used to improve the photoelectric performance of perovskite NCs. Sun et al. synthesized blue emission CsPbCl₃ NCs with Ni²⁺ doping to achieve a near-unity PL QY [22]. Further, the blue PL QYs were significantly enhanced by incorporating Cu²⁺ and Cd²⁺ into the NCs [23,24]. In addition, the incorporation of rare earth ions into perovskite NCs was found to dramatically improve their PL QY and stability [25,26]. Therefore, it is promising to effectively improve the optical and structural properties of perovskite NCs through the metal ion doping engineering.

Mn doped CsPbCl₃ NCs as a typical phosphor were synthesized by Ekimov and Son groups, respectively, in 2016 [27,28]. The doped NCs exhibit a violet band edge emission at about 400 nm and a yellow Mn²⁺ PL band at 600 nm, which can be used to fabricate white LEDs. The maximum value of PL QYs in intrinsic Mn doped CsPbCl₃ NCs reaches up to 60% via varying Mn²⁺ doping concentrations [29,30]. It has been reported that Mn²⁺ emission is attributed to the energy transfer from excitons in CsPbCl₃ host to Mn²⁺ through trap-mediated sensitization, perhaps resulting in a low PL QY at low temperature [[30], [31], [32], [33]]. Recently, the PL QY of Mn doped CsPbCl₃ NCs were improved significantly up to 70 % by the incorporation of Cu²⁺ and Ni²⁺ ions (B-site doping) [[34], [35], [36]]. In particular, the PL QY of Mn doped CsPbCl₃ NCs was enhanced to nearly 100% by post-treatment of CdCl₂ solution [37]. The B-site doping engineering has demonstrated the significant enhancement of PL QY for the Mn doped NCs at 80 K through effective reduction of defects or traps in Mn doped CsPbCl₃ NCs [35,37]. Recently Song et al. enhanced the exciton emission of CsPbCl₃ perovskite NCs by incorporation of Rb⁺ ions [20]. It is very interesting to study the effect of Rb⁺ ions on luminescent and structural properties of Mn doped CsPbCl₃ NCs.

In this work, we report the synthesis of Mn doped CsPbCl₃ NCs with incorporation of Rb⁺ ions for replacing the Cs⁺ ions (Mn:Cs_1-xRb_xPbCl₃, Rb = 0, 0.1, 0.2, 0.3, and 0.4) NCs. The effects of different Rb⁺ ion contents on the structural and optical properties of Mn:CsPbCl₃ NCs were studied by measuring UV-visible absorption and PL spectra, temperature-dependent PL spectra, PL QY, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The experimental results show that incorporation of Rb⁺ into perovskite NCs improves the crystallinity and reduce defects/traps, thereby improving the thermal stability of Mn:CsPbCl₃ NCs.