Abstract
Metal halide perovskites are attracting great interest for the fabrication of light-emitting devices encompassing light-emitting diodes, lasers, and scintillators. As the field develops, perovskite doping emerges as a promising way to enrich the material functionalities and enhance the luminescence yield and tunability. While Mn+2 addition has been well explored, doping with lanthanides has received less attention, even though their intense and line-like luminescence is interesting for a wide range of applications. In this work, we study the doping of NMA2PbBr4 layered perovskites with Eu3+ and Eu3+ tetrakis β-diketonate complex. By exploiting the antenna effect of the naphthalene-based functional cation (NMA = 1-naphtylmethylammonium), direct sensitization of Eu3+ is obtained; nevertheless, it is not very efficient due to the non-optimal energy level alignment with the resonance acceptor level of the lanthanide. Protection of Eu3+ in the form of tetrakis β-diketonate complex grants a more ideal coordination geometry and energetic landscape for the energy transfer to europium in the perovskite matrix, allowing for a nearly 30-fold improvement in luminescence yield. This work sets the basis for new synthetic strategies for the design of functional perovskite/lanthanide host–guest systems with improved luminescence properties.
Highlights
Metal halide perovskites (MHPs) are attracting great interest for a wide range of light-emitting applications including lightemitting diodes (LEDs) and transistors,[1,2] lasers and scintillators.[3,4] The surge in device performance strongly motivates the investigation of synthetic strategies to further enrich the properties of MHPs and provide them with new functionalities.[5]Considering the three-dimensional (3D) MHP structure with general formula ABX3, B-site doping with d-block and f-block elements has been pursued to boost the luminescence properties
Two doping strategies were pursued: (1) substitutional doping with Eu3+ ions to form NMA2PbBr4:Eu was achieved by addition of EuCl3 to the perovskite spin-coating solution; (2) doping with europium chelate was obtained by initially synthetizing the tetrakis β-diketonate complex Eu(tta)4P(Ph)4 [hereinafter Eu(L); Figure 1b], where Eu3+ is coordinated by the four ligands tta = thenoyltrifluoroacetonate, resulting in an anionic complex, with the electric neutrality maintained by the tetraphenylphosphonium P(Ph)[4] counter ion
The preformed complex is added to the spincoating solution to form the doped system NMA2PbBr4:Eu(L)
Summary
Metal halide perovskites (MHPs) are attracting great interest for a wide range of light-emitting applications including lightemitting diodes (LEDs) and transistors,[1,2] lasers and scintillators.[3,4] The surge in device performance strongly motivates the investigation of synthetic strategies to further enrich the properties of MHPs and provide them with new functionalities.[5]. Selection rules are partially relaxed by spin−orbit coupling and crystal-field perturbations which induce mixing of the levels of the 4f configuration with orbitals having opposite-parity wavefunctions, such as 5d orbitals.[21,22,32] Even though these mechanisms allow ED transitions to occur, Eu3+ (likewise other lanthanide ions) suffers from very low absorption coefficients, in turn resulting in weak luminescence This issue is typically solved by (1) including Eu3+ in a strongly asymmetric site of the host matrix[33] and (2) sensitizing Eu3+ with organic ligands, where their larger absorption coefficient is exploited to more efficiently absorb light and transfer energy to the lanthanide (antenna effect),[34] with the energy transfer process typically involving a nonradiative transition from the triplet state of the organic ligand to an excited state of Eu3+.21. This work expands the range of synthetic tools for the development of functional perovskites with improved luminescence properties, with great relevance for applications in light-emitting and photonic devices
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