Efficiently Trap-Mediated Mn2+ Dopant Emission in 2D Single

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C: Energy Conversion and Storage; Energy and Charge Transport

Efficiently Trap-Mediated Mn2+ Dopant Emission in 2D Single-Layered Perovskite (CH3CH2NH3)2PbBr4 Binbin Luo, Yan Guo, Xianli Li, Yonghong Xiao, Xiao-Chun Huang, and Jin Z. Zhang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b02649 • Publication Date (Web): 14 May 2019 Downloaded from http://pubs.acs.org on May 14, 2019

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The Journal of Physical Chemistry

Efficiently Trap-Mediated Mn2+ Dopant Emission in 2D Single-Layered Perovskite (CH3CH2NH3)2PbBr4

Binbin Luoa,*, Yan Guoa, Xianli Lia, Yonghong Xiaoa, Xiaochun Huanga, and Jin Z. Zhangb

a

Department of Chemistry and Key Laboratory for Preparation and Application of

Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, China b

Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: In this work, Mn2+ has been efficiently and homogeneously doped into two dimensional (2D) distorted single-layered EA2PbBr4 (EA: ethylammonium) via a reprecipitation method. Both the doped and undoped 2D layered halide perovskites (LHPs) were characterized using a combination of X-ray, electron microscopy and spectroscopy techniques. The Mn2+-doped EA2PbBr4 (EA2PbBr4:Mn2+) shows a 78% photoluminescence (PL) quantum yield (QY) with complete quench of self-trapped excitons (STEs) emission, due to the efficient exciton trapping by defects created by dopants and small activation energy (~ 9.8 meV) between the defect states and Mn2+ d states. Compared to the long lifetime (~1.5 ms) of Mn2+ emission in CsPbCl3, the lifetime in 2D EA2PbBr4 is found to be ~0.75 ms, resulting from the heavy atom effect. Additionally, the PL QY of Mn2+ emission can be further increased by codping Zn2+ or Cd2+, attributed to a high density of trap states created by codoping facilitating exciton-to-Mn2+ energy transfer. These results reveal the key role of trap states in the energy transfer of Mn2+ doped 2D LHPs.

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1. INTRODUCTION Lead halide perovskites (LHPs) have attracted enormous attention in the past few years owing to their broad versatility of chemical composition and tunability of physical and chemical properties.1-8 By designing the structure of materials and implanting different impurities such as transition metal ions, unique physical and chemical properties can be realized and used for various optoelectronic applications.4, 9-15 Among the transition metal ions, Mn2+ is one of the extensively investigated dopants in II–VI semiconductor nanocrystals (NCs) due to its characteristic emission band with ms scale lifetime and paramagnetism.15 LHPs have a widely tunable bandgap spanning the whole visible range, suggesting that energy transfer from the LHP host to Mn2+ can be easily achieved by adjusting the energy levels of the host. Two previous studies reported in 2016 have successfully synthesized Mn2+-doped CsPbCl3 NCs with a characteristic Mn2+ emission band around 600 nm.16-17 Although these studies have triggered intensive investigations of Mn2+-doped LHPs for improving structural stability,18-19 O2 sensor,20 perovskite solar cells,21 and light-emitting diodes (LEDs),22-23 some anomalous behaviors, such as the enhancement of both bandedge and dopant emission upon low-level doping of Mn2+, and the mechanism of energy transfer are still not well understood. Through cryogenic and time-resolved spectroscopic studies, recent studies suggest that the trap states mediate the energy transfer to sensitize Mn2+ dopants at room temperature in 3D CsPbCl3 host, while direct transfer of energy from bandedge states to dopants occurs at 3



lower temperature (˂ 60 K) due to the large potential barrier (~314 meV) between trap states and Mn2+ d states.24-25 Bakthavatsalam et al. found that the energy transfer is dominated by hot excitons with a timescale of ~340 ps in 2D LHPs,26 indicating that energy transfer from exciton to Mn2+ may not be via a single channel. It has been demonstrated that the formation of self-trapped excitons (STEs) in distorted 2D LHPs is around several ps,27 which is on the same time scale as exciton trapping by shallow defects, but much faster than time scale of the energy transfer from hot excitons/bandedge to Mn2+ dopants. Therefore, the variation of STEs emission intensity can indicate which energy transfer pathway is dominant. In other words, trap-mediated energy transfer would quench the emission of STEs, while it is not anticipated for direct hot excitons/ bandedge-to-Mn2+. In this work, 2D distorted single-layered EA2PbBr4 (EA: ethylammonium) with broad STEs emission was synthesized for the Mn2+ doping investigation. Mn2+-doped EA2PbBr4 (EA2PbBr4:Mn2+) with 78% photoluminescence (PL) quantum yield (QY) accompanied with the complete quench of STEs emission is achieved by tuning the doping level of Mn2+. Temperature-dependent PL spectra indicate that the activation energy is only 9.8 meV between trap states and Mn2+ d states and codoping experiments show that Mn2+ emission can be further enhanced by creating a relatively high density of trap states. These findings reveal the critical role of trap states on the mechanism of energy transfer in Mn2+ doped LHPs.

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2. EXPERIMENTAL SECTION Materials: All the chemicals were used as received without further purification, including PbBr2 (99.99%, Aladdin), PbCl2 (99.99%, Aladdin), EABr (98%, TCI), EACl (99%, energy chemical), CH3CH2 (40%, TCI), MnCl2 (99%, Aladdin), MnBr2 (95%, Alfa Aesar),

HCl

(37.5%,

Xilong

Scientific),

toluene

(AR,

Xilong

Scientific),

N,N-dimethylformamide (DMF, spectroscopic grade, 99.9%, Aladdin). Synthesis of 2D EA2PbBr4 single crystals: In a 15 ml vessel, PbBr2 (91.7 mg, 0.20 mmol), EABr (126.0 mg, 1 mmol) and 2 drops of HBr were added. The vial was tightly caped and heated up to 160 ℃ in 30 min and lasted for 2 h. The vial was then cooled to room temperature and remained undisturbed for a week. Colorless rectangular shaped crystals were harvested. Synthesis

of

2D

EA2PbBr4,

EA2PbBr4:Mn2+,

EA2PbBr4:Mn2+/Zn2+

and

EA2PbBr4:Mn2+/Cd2+ powders: 2D single-layered EA2PbBr4 were synthesized via an anti-solvent precipitation. Typically, PbBr2 (0.10 mmol) and EABr (0.20 mmol) were dissolved into 200 μl DMF to prepare the precursor solution. Then the precursor solution was added into 10 ml of toluene under vigorous stirring. The solid product was precipitated and separated via centrifugation at 6000 rpm for 5 min and washed once with toluene under sonication. At last, the powder was collected by centrifugation and dried in a vacuum oven (60 ℃ ) overnight for further optical characterization. The synthetical strategy of EA2PbBr4:Mn2+, EA2PbBr4:Mn2+/Zn2+ and EA2PbBr4:Mn2+/Cd2+ is almost 5



same as that of undoped EA2PbBr4 except replacing desired amount of PbBr2 with MnBr2, ZnBr2 or CdBr2. For doped EA2PbBr4 series, the final molar ratio of nEABr:(nPbBr2+nXBr2: X = Mn2+, Zn2+ and Cd2+) is kept at 3:1. For example, for the synthesis of EA2PbBr4:5%Mn2+, 0.30 mmol EABr mixed with 0.095 mmol PbBr2 and 0.005 mmol MnBr2 were dissolved in 200 μl DMF, the following procedure is same to that of pure EA2PbBr4. Characterization: Absorption and PL spectra of the samples were collected on UV-vis spectrum (Lambda 950, PERKIN ELMER) and fluorescence spectra (PTI QM-TM, Photon Technology International), respectively. Absolute PL QY was recorded on HAMAMATSU C11347 spectrometer with integrating sphere. Standard dye sample (Rhodamine 6G) was tested first to calibrate the setup, then EA2PbBr4:Mn2+ powders were characterized three times and the results are averaged. The PL QY of EA2PbBr4:Mn2+ powders were also tested both in Shantou University and Sun Yat-Sen University to check the reproducibility. Electron Paramagnetic Resonance (EPR) spectrum was tested on Bruker A300. X-Ray diffraction (XRD, MiniFlex 600, Rigaku) analysis was used to obtain the crystalline phase. The scanning angle range was 4-50º (2θ) with a rate of 3º/min. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was conducted to determine the content of Mn2+ and Pb2+. Field emission scanning electron microscopy (FESEM, Gemini 300, ZEISS) and energy dispersive spectroscopy (EDS) were carried out to obtain the morphology and elemental distribution. Luminescence lifetime measurements were collected on Edinburgh 6


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Instruments (FLS920). Powder samples with same weight were compressed into films with two quartz slides and used for further PL lifetime test. The obtained PL decay curves are fitted with single or double exponential function as given in the following expression:

where I(t) is the PL intensity at time t, t is the time, Ai represents the relative weights of the decay components at t = 0, τi represents the decay time for the exponential components. The average lifetime is calculated based on the expression below:

3. RESULTS AND DISCUSSION 3.1 Crystal structure and optical properties of EA2PbBr4 EA2PbBr4 single crystals were only obtained using EABr with the molar ratio in excess compared to that of PbBr2. Based on single crystal X-ray diffraction (XRD), EA2PbBr4 crystallizes into monoclinic crystal system (P21/c) with orientation. The detailed structural parameters are summarized in Table 1. Table 1. Structural data of single-layered EA2PbBr4. Structural parameter

EA2PbBr4

7



aR 1

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temperature

298 K

formula weight, g/mol

619.02

Wavelength, Å

Cu Kα (λ = 1.54184 Å)

crystal system

monoclinic

space group

P21/c

a, Å

11.7549(2)

b, Å

8.2374 (1)

c, Å

8.1699(1)

, °

108.855(2)

cell volume, Å3

748.64(2)

Z

2

density

2.7459 g/cm3

completeness to theta = 74.38

95.9%

GOF

1.056

Rint

0.0301

final R indices [I > 2sigma(I)]a

R1 = 0.0457, wR2 = 0.1314

R indices (all data)a

R1 = 0.0472, wR2 = 0.1334

largest diff. peak and hole, e Å-3

2.226/-2.561

= ∑||Fo| − |Fc||/∑|Fo|; wR2 = {∑[w(Fo2 – Fc2)2]/∑[w(Fo2)2]}1/2

EA2PbBr4 consists of corner-shared [PbBr6]4- separated with bilayers of EA+ as spacer 8


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cations, as shown in Figure 1a. Compared to 3D lead bromide perovskites, the lead bromide framework in EA2PbBr4 is highly twisted (Figure 1b), resulting from the dual interaction including hydrogen bonding (average length of hydrogen bonds: ~2.6 Å) and electrostatic interaction between ammonium and [PbBr6]4- octahedra. The Pb-Br-Pb bond angles strongly deviate from the planar geometry with an average angle of ca. 150.56°. Different from the outer layers of EA4Pb3Br10,28 the [PbBr6]4- units maintain a quasi-ideal geometry of octahedron with an average length of ca. 2.99 Å, which is close to the bond length of 3D structure (ca. 2.97 Å). Anti-solvent precipitation method was modified to prepare EA2PbBr4 powders.29 The precursor molar ratios have a great effect on the products, as shown in Figure S1 and S2. Although no diffraction peaks of impurity are observed in the sample prepared with stoichiometric ratio (nEABr:nPbBr2 = 2:1), the absorption band of three-layered EA4Pb3Br10 can be found. Therefore, the molar ratio of nEABr:nPbBr2 = 3:1 was used for the synthesis of EA2PbBr4 powder. Powder X-ray diffraction (PXRD) patterns of the samples are shown in Figure 1c. The diffraction peaks agree well with simulated patterns of EA2PbBr4 and no any other diffraction peaks are observed, showing the high purity of as-prepared sample. The wrinkled feature at the edge of crystals denoted by red dash circle can be clearly observed from SEM image (Figure 1d), further indicating the 2D morphology of EA2PbBr4.

9



Figure 1. (a) Crystal structure of EA2PbBr4. (b) Bond length and angle of lead bromide framework in EA2PbBr4. (c) PXRD patterns of as-prepared products. (d) SEM image of EA2PbBr4.

For layered LHPs, their optical properties are strongly dependent on their crystal structure, especially in terms of number of layers. EA2PbBr4 shows a sharp excitonic absorption (Figure 2) similar to that of single-layered LHPs peaked at 396 nm (~ 3.13 eV) with different spacer cations.30-32 Upon UV excitation at 360 nm, a narrow peak at 415 nm and a broad PL band spanning the entire visible range can be observed, which is attributed to the STEs emission due to the highly distorted structure. The white light emission has been widely observed in other distorted single-layered LHPs.12, 27-28, 30, 33 10


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Figure 2. Absorption and PL spectrum (ex = 360 nm) of EA2PbBr4. Inset: the photograph of as-prepared EA2PbBr4 under UV light.

3.2 Mn2+ doping of EA2PbBr4 Previous studies have suggested that the high PL QY of CsPbCl3:Mn2+ nanocrystals (NCs) originates from the good alignment between the host bandgap and d-d transition of Mn2+.34-35 With the substitution of Cl- with Br- (bandgap decreasing), the intensity and PL QY of Mn2+ dopant emission dropped progressively,16, 35 implying a mismatch in energy levels between host bandgap and excited states of Mn2+ dopant. Therefore, the bandgap alignment plays an important role in determining the efficiency of energy transfer from host to Mn2+ dopants. 2D EA2PbBr4 exhibits a similar bandgap as CsPbCl3 according to its absorption spectrum, suggesting that 2D EA2PbBr4 may function as a potential host material for Mn2+ dopant. What’s more, the intrinsic pathway of energy transfer of Mn2+ can be 11



determined by examining the quench effect of Mn doping on the white light emission of EA2PbBr4 due to the comparable lifetime between exciton trapped by lattices and defects. SEM image (Figure S3) was taken to present more morphological details of Mn2+ doped EA2PbBr4. Micron-sized crystals with plicate surface were observed, implying the layered structure of EA2PbBr4:40%Mn2+ remains upon Mn2+ doping. With increasing nominal dopant levels of Mn2+, the PXRD (Figure 3a) of EA2PbBr4:Mn2+ shows small shift towards high degree, attributed to the small radius of Mn2+ with respect to Pb2+. Electron paramagnetic resonance (EPR) spectra (Figure 3b) of EA2PbBr4:Mn2+ show the hyperfine splitting without significant interference, which rules out the existence of Mn2+ with a different coordination environment and suggests the weak Mn-Mn exchange interaction.36 Since the strength of Mn-Mn exchange interaction highly depends on the distance of Mn2+ ions,37 the weak Mn-Mn interaction observed in 2D (EA)2PbBr4 is ascribed to the large interlayer distance (~11 Å) and homogenous doping of Mn2+. The splitting energy with ~93 G is close to that in Mn2+-doped CsPbCl3 NCs and bulk samples, demonstrating the successful replacement of octahedrally coordinated Pb2+ by Mn2+ ions.17, 38 Energy dispersive spectroscopy (EDS) mapping (Figure 3c) also indicates the uniform distribution of Mn2+ in EA2PbBr4. Interestingly, the doping efficiency (Table S1) of Mn2+ in 2D EA2PbBr4 is much higher than that of CsPbCl3 NCs, in which only a small amount of added Mn2+ can be incorporated into the crystal lattice.14 It is believed that the 2D single-layered feature of EA2PbBr4 plays a key role in promoting the substitution process since all the Pb2+ sites 12


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can be exposed and exchanged with Mn2+ in the synthesis. The fast substitution is also evidenced by the easy synthesis of Mn2+-doped EA2PbBr4 from simply grinding EABr, PbBr2, and MnBr2 precursors together. As shown in the Video 1 provided in Supporting Information (SI), intense orange light is immediately observed after under UV light, which cannot be realized in 3D CsPbCl3 and MAPbCl3.

Figure 3. (a) PXRD patterns of EA2PbBr4:Mn2+ with different dopant concentrations. Dashed line indicates the shift of diffraction peak. (b) EPR spectrum of EA2PbBr4:Mn2+ at room temperature. (c) EDS mapping of EA2PbBr4:20%Mn2+. 13



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In the absorption spectra, a sharp absorption edge with an onset at 430 nm (Figure 4a) is observed for all Mn2+ doped samples, attributed to the first excitonic absorption of the host. Correspondingly, a broad (FWHM = 81 nm) and characteristic Mn2+ dopant emission (Figure 4b) at 616 nm can be found after Mn2+ doping, resulting from the Mn2+ d-d emission corresponding to the spin-forbidden

4T 6A 1 1

transition.35,

39-42

Unexpectedly, with increasing the input concentration of Mn2+ dopant from 1 to 60 at.%, the STEs emission is completely quenched. As a result, the total PL QY of the EA2PbBr4:Mn2+ samples reach up to 78% with 40 at.% Mn2+ nominal doping level, which is higher than that of most reported host systems.23, 31, 39, 43-45 Some representative photographs of the EA2PbBr4:Mn2+ samples under room light and UV light are shown in Figure S4, respectively. Intense orange light is observed when the samples are placed under UV light (ex = 365 nm). It has been demonstrated that the formation of STEs from free excitons occurs on ps time-scales in 2D LHPs,27 while the transfer time of exciton-to-Mn2+ is around hundreds ps.43, 46 Compared to the much faster formation rate of STEs, the slower transfer time of exciton-to-Mn2+ indicates that Mn2+ doping should not have significant impact on the STEs emission. The anomalous behavior and high PL QY of Mn2+ emission suggest that an intermediated state has been introduced simultaneously upon Mn2+ doping that are more competitive than the formation of STEs for exciton trapping. Usually, doping impurities creates high density of defect states, which trap excitons around several to tens ps time scales.47 Therefore, this intermediated states are very likely trap states. 14


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The PL excitation (PLE) spectra (Figure 4c) of EA2PbBr4:Mn2+ samples collected at 616 nm show features that resemble the absorption band, implying that the Mn2+ dopant emission arises from the absorption of the host. Note that a weak and broad PLE peak at 435 nm is clearly observed and the intensity presents a positive correlation with the concentration of Mn2+, attributed to the absorption of trap states created by Mn2+ doping. This result indicates that the energy of Mn emission can derive from the absorption of trap states. The much lower intensity suggests that the energy of Mn2+ emission is mainly derived from the EA2PbBr4 bandedge absorption.

Figure 4. (a) Absorption and (b) Normalized PL spectra (ex = 360 nm) of EA2PbBr4:Mn2+ with different nominal Mn2+ concentration. (c) PLE spectra (em = 616 nm) of EA2PbBr4:Mn2+ with different doping level. PL decay curves of EA2PbBr4:Mn2+ monitored at different wavelength (d) 415 nm, (e) 616 nm. (f) Temperature-dependent PL 15



spectra of EA2PbBr4:40%Mn2+. Inset: Boltzmann analysis of Mn2+ PL intensity as a function of T.

To better understand the energy transfer process, time-resolved PL was conducted as shown in Figure 4d. The PL decay curves of the emission with maximum intensity show double-exponential fit with average lifetimes ranging from 4.0 to 1.4 ns when the doping level of Mn2+ was increased from 0 to 60 at. %. The great decrease in average lifetime implies the highly efficient trapping of excitons by defects, which transfer the energy to Mn2+ sites subsequently. As for the Mn2+ emission, all the PL lifetimes of EA2PbBr4:Mn2+ samples can be fitted with a single exponential (Figure 4e). The lifetimes are calculated to be ~0.747 ms, caused by the spin-forbidden transition from 4T1 to 6A1.31 Interestingly, varying the Mn2+ doping concentration does not seem to have a significant influence on the lifetime of Mn2+ dopant emission. The constant lifetime of Mn2+ emission in our case further indicates the negligible Mn2+-Mn2+ dipole-dipole interaction in EA2PbBr4 host. Compared to the PL lifetime (~1.5 ms) of Mn2+ dopants in 3D CsPbCl3 system,23 the lifetime of EA2PbBr4: Mn2+ is much shorter, usually attributed to the Mn2+-Mn2+ interaction upon high doping level.31, 35, 48 However, this may not be the reason in our case since no significant decrease of lifetime and redshift of Mn2+ emission were observed with higher Mn2+ doping concentration.45 The reason for the reduction of Mn2+ PL lifetime from ~1.5 ms of CsPbCl3 system to 0.75 ms of EA2PbBr4 host could be the heavy atom effect that increases the rate of intersystem crossing, as reflected by the 16


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fact that the lifetime of Mn2+ increases from 0.767 to 2.896 ms once Br is progressively replaced by Cl in our case (Figure S5). A recent study demonstrated that the heave atom effect can enhance the intersystem crossing from perovskite host to organic ligand to enhance the room-temperature phosphorescence.49 In addition, the central wavelength of the Mn2+ emission band can be slightly tuned from 616 nm (orange light) to 630 nm (pink light) by progressively substituting Br with Cl (Figure S5a), ascribed to the difference of strength of ligand filed. The temperature-dependent PL spectrum (Figure 4f) of EA2PbBr4:40%Mn2+ sample enables us to gain deeper insight into the energy transfer mechanism of EA2PbBr4:Mn2+. The PL spectrum at 77 K exhibits a sharp emission peak at 395 nm and a broad emission band with a maximum at 635 nm, arising from the bandedge emission of single-layered EA2PbBr4 and Mn2+ d-d transition, respectively. The red-shift of Mn2+ dopant emission stems from the enhancement of ligand field strength due to the contraction of octahedra.44, 50

The progressive decrease of Mn2+ emission confirms the thermally activated excitation

mechanism of dopants. An activation energy ΔEc is calculated to be 9.8 meV based on the Boltzmann analysis shown in the inset of Figure 4f, which is much smaller than that (~314 meV) in CsPbCl3 NCs.24 Such small potential barrier enables the efficient transfer of excitons to Mn2+ and high PL QY at room temperature.

2.4 Enhancing Mn2+ emission through codoping The results shown above suggest that trap states play a key role in energy transfer from 17



host to the dopant. Therefore, a relatively high density of trap states seems to facilitate energy transfer and thereby enhance Mn2+ emission. Usually, dopant emission is not observed in transition metal ions with d10 filling configuration. Therefore, Cd2+ is codped with 5 at.% Mn2+ into EA2PbBr4 spontaneously to further understand the sensitization mechanism. As shown in Figure 5a, Mn2+ and Cd2+ codoped samples with homogeneous distribution can be obtained. ICP-AES results (Table S2) show that varying the doping level of Cd2+ in the range of 0%~15% has limited impact on the content of Mn2+. As expected, a significant enhancement of Mn2+ emission (Figure 5b) was observed upon codoping Cd2+, while further increasing the doping level reduces the intensity. This behavior is also observed for Zn2+ and Mn2+ codoped samples (Figure S6). The PL QY rises from 41.1% to 62.9% once increasing the doping level of Cd2+ from 0 to 10 at.%, demonstrating the trap-mediated energy transfer mechanism. As for optimized 40 at.% Mn2+ doped EA2PbBr4, the PL QY can be slightly improved when codpoing Cd2+ with a low doping level in the range of 1-5 at.% (Figure 5c) since a high density of defects have been created by Mn2+ dopants. However, further increasing the concentration of Cd2+ diminishes the QY of Mn2+ dopant emission, which is ascribed to the deterioration of crystal quality of the host and also the competition effect of Cd2+ in the doping reaction.

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Figure 5. (a) EDS mapping and (b) PL spectra of Mn2+ and Cd2+ codoped EA2PbBr4 samples, the PL intensity located at 415 nm are normalized. The doping level of Mn2+ is kept at 5 at.% and the content of Cd2+ is varied from 0 to 15 at.%. (c) PL QY of EA2PbBr4:40% Mn2+ with different doping levels of Cd2+.

4. CONCLUSION In summary, 2D single-layered EA2PbBr4 with broad STEs emission has been prepared via a reprecipitation method. By doping Mn2+ into 2D single-layered EA2PbBr4, the STEs 19



emission is completely quenched due to the efficient exciton trapping by the induced shallow defects, resulting in 78% PL QY of Mn2+ dopant emission. The activation energy between trap states and Mn2+ d states is calculated to be ~9.8 meV, which is much smaller than that in 3D CsPbCl3 host. Moreover, codoping Zn2+/Cd2+ into EA2PbBr4:Mn2+ also enhance the Mn2+ emission, further supporting the trap-mediated energy transfer mechanism. These results indicate the importance of trap states in host-to-dopant energy transfer in Mn2+ doped 2D LHPs. AUTHOR INFORMATION Corresponding Author * E-mail：[email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This project was supported by National Natural Science Foundation of China (NSFC: 51702205) and STU Scientific Research Foundation for Talents (NTF17001). We thank Mingyang Li (Sun Yat-Sen University) for the TRPL measurements and Tongtong Xuan (Sun Yat-Sen University) for the PL QY characterization.

ASSOCIATED CONTENT Supporting Information 20


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XRD patterns, absorption and PL spectra, SEM images and ICP-AES analysis data for doped EA2PbBr4 samples. Notes The authors declare no competing financial interest.

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