We study the stability of the rare-earth dopant, Eu, in metal-halide perovskite CsPbBr3 with cubic and orthorhombic structures from first-principles calculations. In these perovskites, Eu is substitutionally doped on Pb sites because of their comparable ionic sizes which lead to only a small strain in the doped system. Accordingly, our results show that the cost of Eu doping is quite small compared to the values in other common hosts such as GaN. This makes these perovskites excellent candidates to develop rare-earth doped semiconducting materials for bright luminescence as it has also been observed recently in the case of thin films of CH3NH3Pb1-xEuxI3, Eu-doped quantum dots of CsPbBr3, and nanocrystals of CsPbCl3 in addition to their outstanding properties for applications in solar cells. © 2019 American Chemical Society.

Vijay Kumar

Center for Informatics

Bala A.

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Shiv Nadar University

Journal of Physical Chemistry C

Recent experiments on Eu-doped nanocrystals of CsPbX3 (X = Cl, Br) show that Eu exists in the 3+ oxidation state even though it substitutes Pb, which is in the 2+ state in these perovskites. Therefore, the question arises, what is it that leads to the formation of Eu3+ in the nanocrystals of these materials? In order to understand this, we have studied the doping of Eu in a slab (∼1.8 nm thick) of CsPbBr3 using ab initio calculations and explored various possibilities that could lead to the formation of Eu3+ and the occurrence of f-f transitions. These include (1) the presence of a Cs vacancy, (2) the existence of H or OH due to moisture, (3) substitution of O at the surface halogen site, and (4) the possibility of excess halogen around Eu. It is found that the presence of surface oxygen is the most likely reason for the observation of Eu3+ in these nanolayers. Our results show the presence of partially occupied spin-up f states and a magnetic moment of 6.48 μB on Eu that could lead to the possibility of f-f transition in these doped systems. A similar result has also been obtained for Eu doped in CsPbCl3 nanolayers. The calculated change in energy when defects/impurities are present is a favorable indication of finding H, OH, and Br as interstitials and O as substitutional entities but Cs vacancy is unlikely. Additionally, we find that the doping of Eu in nanolayers does not affect the atomic structure, and the cost of doping is also very small, making these perovskites very promising materials for light-emitting diodes and other solid-state lighting applications. © 2020 American Chemical Society.

ACS Applied Nano Materials

A Study of Eu Doping in Nanolayers of CsPbBr3using Ab Initio Calculations to Understand f-f Transitions in Eu3+-Doped Nanocrystals for Light-Emitting Diodes

Thin layers of inorganic halide perovskites An+1MnX3n+1 (n = 1-6, A= Cs, M = Pb and Sn, and X = Cl, Br, and I) have been studied in orthorhombic and cubic phases along with layers of monoclinic CsSnCl3. It is found that one-unit-cell-thick layers have low stability except the monoclinic CsSnCl3 for which formation energy is slighly less than the bulk value. However, Cs2PbI4 is unstable in both cubic and orthorhombic phases. The formation energy for n &gt; 3 becomes comparable to bulk, but the inclusion of spin-orbit coupling is found to be important for the stabilization particularly for layers with Pb. Importantly, layers of environmentally friendly Sn-based systems have similar values of formation energy in the orthorhombic and cubic phases as well as similar band gaps which make them good materials for solar cell applications as temperature range changes during their operation. The studied 66 cubic and orthorhombic nanosystems have direct band gap (0.6-2.9 eV) using generalized gradient approximation for the exchange-correlation functional, but the use of the HSE06 method increases the band gap. The reduced dimensionality leads to elongation (contraction) of MX6 octahedra perpendicular (parallel) to the plane of the layers and an increase in the band gap. The presence of surface makes the hybridization between M s and X p orbitals near the valence band maximum stronger than in bulk which is good for light absorption. The effective mass of the electrons and holes is very light which augers well for the transport properties. Lead-based systems have larger band gap, and these can be useful in applications such as light-emitting diodes. © 2018 American Chemical Society.

Atomic and Electronic Structure of Two-Dimensional Inorganic Halide Perovskites An +1M n X3 n +1 (n = 1-6, A = Cs, M = Pb and Sn, and X = Cl, Br, and I) from ab Initio Calculations

Chemistry of Materials

Metal-Doped Lead Halide Perovskites: Synthesis, Properties, and Optoelectronic Applications

RSC Advances

CH3NH3Pb1−xEuxI3 mixed halide perovskite for hybrid solar cells: the impact of divalent europium doping on efficiency and stability

Chemical Communications

CsPbBr3:xEu3+ perovskite QD borosilicate glass: a new member of the luminescent material family

Nano Letters

Doping Lanthanide into Perovskite Nanocrystals: Highly Improved and Expanded Optical Properties

Stability of the Eu2+ Dopant in CsPbBr3 Perovskites: A First-Principles Study