Temperature-Dependent Photoluminescence and Energy-Transfer Dynamics in Mn²⁺-Doped (C₄H₉NH₃)₂PbBr₄ Two-Dimensional (2D) Layered Perovskite

Abstract

Reported here are the low-temperature photoluminescence (PL), energy-transfer mechanism, and exciton dynamics of Mn 2+ -doped two-dimensional (2D) perovskites that show interesting differences from their three-dimensionally doped counterpart. Dopant emission in 2D system shows increased PL intensity and shortened lifetime with increase of temperature and strong dopant emission even at low temperatures. Transient absorption (TA) spectroscopy reveals the dominant role of "hot" excitons in dictating the fast energy-transfer timescale. The operative dynamics of the generated hot excitons include filling up of existing trap states (shallow and deep) and energy-transfer channel from hot excitons to dopant states. Global analysis and target modeling of TA data provide an estimate of excitons (hot and band edge) to a dopant energy-transfer timescale of ∼330 ps, which is much faster than the band edge exciton lifetime (∼2 ns). Such fast energy-transfer timescale arises due to enhanced carrier exchange interaction resulting from higher exciton confinement, increased covalency, and involvement of hot excitons in the 2D perovskites. In stark contrast to three-dimensional systems, the high energy-transfer rate in 2D system results in high dopant emission intensity even at low temperatures. Increased intrinsic vibronic coupling at higher temperatures further supports efficient Mn 2+ sensitization that ultimately dictates the observed temperature dependence of the dopant emission (intensity, lifetime).

Doped Lead Halide White Phosphors for Very High Efficiency and Ultra‐High Color Rendering

“…Such results further confirm that the emission of Mn in hybrid metal halides is strongly coupled with the excitons.T oexhibit an intense red emission from the Mn dopants,t he photoluminescence of the host (that is,e xcitonic emission) should also be intense.I nterestingly,av ery low amount of dopants (less than 0.030 %) are sufficient to obtain high PLQYs.Such enhanced exciton-dopant exchange coupling interactions is probably due to high quantum confinement as excitons can diffuse in only one dimension. [33] Thee xact nature of exciton-dopant coupling for hybrid metal halides remains unclear. Some authors reported that energy transfer is occurring only between free excitons and Mn because the self-trapped exciton states are indirect transient states with unpopulated ground states that could block electron exchange in Dexter energy transfer.…”

“…[37] Thus,t ou nravel the mechanism of luminescence in our Mn doped lead halide, temperature-dependent PL measurements were performed for (TDMP)PbBr 4 (Supporting Information, Figure S10) and (TDMP)PbBr 4 :Mn (Figure 3a,b). [33] At low temperature (below ca. 120 K), only one emission band originating from self-trapped excitons can be observed for both doped and undoped materials.Athigher temperatures (above ca.…”

“…[17] In parallel, the selection rule of the forbidden transition of the Mn dopant is relaxed owing to vibronic coupling. [33] Thus,t he rate of energy transfer exciton-dopant increases and leads to the increase of the Mn emission with temperature.Above ca. 120 Katwhich Mn emission appears, the evolutions with temperature of FE or STE emissions differ when comparing (TDMP)PbBr 4 and (TDMP)PbBr 4 :Mn (Supporting Information, Figure S11).…”

“…[14,[27][28][29][30][31][32] Of particular interest, Mn 2+ can be used to dope most of the hybrid lead halides by substituting the metal element. [14,31,33] This ion is commonly used to improve the photoluminescence quantum yield (PLQY) or/ and the stability of perovskite lattices. [14,34,35] Furthermore,an improvement of the CRI is usually observed.…”

Neoteric Mn2+‐activated Cs3Cu2I5 dazzling yellow‐emitting phosphors for white‐LED

“…The thermally activated exciton and its energy transfer to the Mn 2+ ions can be responsible for the enhanced emission intensity when the temperature was in the range of 363‐423 K (as shown in the inset of Figure C). From previous reports, one knows that the exciton could be easily activated at elevated temperature, and then it transferred the energy to the Mn 2+ ions, resulting in the increased emission intensity. Most noticeably of all, the emission intensity at 423 K maintained around 64.5% of its initial value at 303 K which means that the Mn 2+ ‐activated Cs 3 Cu 2 I 5 halides exhibited strong resistance to the temperature.…”