Low-Temperature Energy Transfer via Self-Trapped Excitons in Mn²⁺-Doped 2D Organometal Halide Perovskites

Abstract

We investigate the mechanisms of energy transfer in Mn2+-doped ethylammonium lead bromide (EA2PbBr4:Mn2+), a two-dimensional layered perovskite (2DLP), using cryogenic optical spectroscopy. At temperature T > 120 K, photoluminescence (PL) is dominated by emission from Mn2+, with complete suppression of band edge (BE) emission and self-trapped exciton (STE) emission. However, for T < 120 K, in addition to Mn2+ emission, PL is observed from BE and STEs. Data further reveal that for 20 K < T < 120 K, STEs form the most dominant routes in assisting energy transfer (ET) from 2DLP to Mn2+ dopants. However, at higher Mn2+ concentration, higher activation energies indicate defect states come into play, successfully competing with STEs for ET both from BE to STE states and from STE to Mn2+. Finally, using polarization-resolved spectroscopy, we demonstrate optical spin orientation of the Mn2+ ions via ET from 2DLP excitons at zero magnetic field. Our results reveal fundamental insights on the interactions between quantum confined charge carriers and dopants in organometal halide perovskites.

Power-Dependent Photoluminescence Efficiency in Manganese-Doped 2D Hybrid Perovskite Nanoplatelets

“…As shown in Figure a, a characteristic broad emission at 610 nm attributed to the Mn 2+ d–d ( 4 T 1 – 6 A 1 ) transition , was observed, which changed the overall emission color of the solution from purple or deep blue to orange or pink (Figure S4). Mn 2+ dopant emission has been previously observed between 580 and 620 nm in different semiconductors, ,,,,,− with variations attributed to differences in the ligand field environment. ,, No absorption feature associated with the dopant state , was observed in our work, presumably due to the low oscillator strength of the spin-forbidden Mn 2+ d–d transition …”

Emerging doping strategies in two-dimensional hybrid perovskite semiconductors for cutting edge optoelectronics applications

“…Unlike peculiar lead-based 3D bulk perovskites, the band edge PL peak of the Mn 2+ doped EA 2 PbBr 4 perovskite shows a red shi, whereas STE and Mn 2+ emission related peaks suffer from a blue shi with increasing temperature due to enhanced ligand eld strength resulting from the contraction of the octahedra. 112 The red shi of the band edge peak was believed to be a characteristic of single layer perovskites as earlier it was observed in the undoped system also. The bandgap or PL peak shi of 2D perovskites with increasing temperature is dependent on the perovskite layer number as it switches from a blueshi to a redshi from n ¼ N to n ¼ 1, since the bandgap evolution of the semiconductor with temperature is collectively inuenced by the thermal expansion of the lattice resulting in a blue shi and exciton-phonon interaction which has a negative coefficient inducing a red shi.…”

“… 112 The PL emission intensity of both band edge and STE decreased with increasing T , while that of Mn 2+ concurrently increased, suggesting two pathways of energy transfer: direct energy transfer from the band edge to Mn 2+ and energy transfer to the Mn 2+ band through STEs. 112 Band edge emission completely quenched around 120 K and the activation energy barrier of charge transfer (30–40 meV) from the band edge to Mn 2+ was found to be greater than the thermal energy at low temperature and ambient temperature, which ruled out the possibility of direct energy transfer from the band edge to Mn 2+ dopants. 112 Hence, the main route of energy transfer from the band edge to dopants is followed through STE.…”

“… 111 Mn 2+ doped EA 2 PbBr 4 perovskite exhibited a little different behavior where the charge transfer was occurring through STE (self-trapped exciton). The role of STEs in host-to-dopant energy transfer was investigated in the Mn 2+ doped EA 2 PbBr 4 perovskite in the temperature range of 20–100 K. 112 The room temperature PL of the Mn 2+ doped EA 2 PbBr 4 perovskite demonstrated no other emission except a strong emission centered around 610 nm from the Mn 2+ d–d spin forbidden transition confirming the uninhibited energy transfer between the host and the dopant ions. 112 Interestingly, PL at T = 30 K highlighted three distinct regions showing emission corresponding to the direct band edge emission, sideband form STEs, and Mn 2+ dopants ( Fig.…”

Electron Auto-Localization Tailored by Its Thermal Energy: Dynamic Matrix Approach (DMA)

“…Recent investigations show that polaron characteristics may decrease with temperature [16] [17] [18] [19] and a transition from a quantum phase to classical phase predicted [19]. One of the prominent results is seen in ref [20] where the authors investigate experimentally the mechanisms of energy transfer in Mn 2+ doped ethylammonium lead bromide. It is observed that for large temperature, photoluminescence is dominated by emission from Mn 2+ , with a complete suppression of band edge emission and self-trapped exciton emission.…”