Insights of Doping and the Photoluminescence Properties of Mn

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Perspective

Insights of Doping and the Photoluminescence Properties of Mn Doped Perovskite Nanocrystals Samrat Das Adhikari, Amit K. Guria, and Narayan Pradhan J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b00182 • Publication Date (Web): 16 Apr 2019 Downloaded from http://pubs.acs.org on April 16, 2019

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The Journal of Physical Chemistry Letters

Insights of Doping and the Photoluminescence Properties of Mn Doped Perovskite Nanocrystals Samrat Das Adhikari, Amit K. Guria* and Narayan Pradhan* School of Materials Science and Technical Research Center, Indian Association for the Cultivation of Science, Kolkata INDIA 700032

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ACS Paragon Plus Environment

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Abstract: Doping Mn2+ in semiconductor nanocrystals is widely known for the long lifetime Mn d-d orange emission. While this has been extensively studied for chalcogenide nanostructures, recently this was also extended to perovskite nanocrystals. Being CsPbCl3 has wide bandgap, the exciton energy transfer was found more efficient; but the dopant induced photoluminescence was also obtained for layered perovskites and quantum confined CsPbBr3 nanocrystals. Significant advances have been achieved in understanding the physical insights of doping following various approaches and optimizing the conditions for obtaining intense dopant emission. In addition, several new properties associated with these doped nanocrystals were also reported and modulating the compositions the host bandgap as well as the dopant emission positions were also tuned. Keeping all these developments in mind, this perspective focused on the insights of doping and the photoluminescence properties of Mn2+ doped perovskite nanocrystals. In addition, this also proposed the possible future prospects of both synthesis and optical properties of these nanomaterials.

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Doping Mn2+ in semiconducting materials has been extensively studied for decades.1-5 This has its very unique identity having long lifetime orange emission originated from its dstates.3, 6-7 Excitation of the host and emission from the dopant remained the most striking feature of these materials and the emission energy remained less concerned with the bandgap of hosts.8-9 From the most widely studied ZnS host to other chalcogenide nanocrystals, insights of doping of Mn2+ in the crystal lattice and the obtained new photoluminescence properties were largely understood.10-11 In the recent developments, the doping has also been extended to perovskite nanocrystals. Among these, the high bandgap perovskite, CsPbCl3, became the ideal host for efficiently transferring its exciton energy and widely studied for last couple of years.12-14 The high temperature synthesis method reported by Kovalenko and co-workers15 was the backbone and the same was extended to Mn doping originally by Klimov’s research group.12 This breakthrough of the doping in perovskites was also summarized earlier;7 but with course of time significant investigations of the doping and the dopant induced properties were studied. Several new methods have been developed,14,

16-18

impact of different additives on doping are

established, the temperature dependent new observations in the photoluminescence(PL) has been obtained and the doping has also been extended to layered perovskites as well as to CsPbBr3 nanocrystals.14, 18-25 Keeping all these developments in mind, this perspective focused on the challenges tackled and remained in the synthesis, the obtained dopant induced photoluminescence properties and its tunability, and this focused the extended doping in other hosts including layered perovskites. Insights of Mn2+ doping in CsPbCl3 nanocrystals were first analyzed and several chemical processes involved in insertion of the dopant inside the lattice were summarized

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schematically in Figure 1a. The first and common approach of using MnCl2 with certain concentration along with Pb and Cs precursors was the most optimized one which led to the doped nanocrystals following insitu or simultaneous doping along with the formation of host nanocrystals (Figure 1a, Scheme-I).12, 18 The key feature in this approach was the rich in halide ions in the reaction system, mostly came from MnCl2. Moreover, excess MnCl2 in bulk solution was required for competing with Pb even for just a few percent was inserted in the crystal lattice.26 For reducing the Mn precursor concentration, different chloride sources were used which also helped in efficient doping in the host CsPbCl3 nanocrystals (Figure 1a, Scheme-II). Further, using alkylammonium ions and varying its concentration, doping efficiency was enhanced and this also helped in tuning the dimensions of the host nanocrystals. Figure 1b presents the digital image of the reaction flask under illumination having Mn doped CsPbCl3 nanocrystals obtained in this approach.14 While this reaction was carried out at higher temperature, Mn could also be inserted inside the CsPbCl3 nanocrystals using HCl at room temperature.25 Further, interesting observations were obtained on Mn doping achieved via post-synthetic cation exchange with the incorporation of other metal/non-metal chlorides (Figure 1a, Scheme-III).27 These chloride salts helped in inserting Mn2+ inside the host perovskites. In addition to all these methods, mixed halide approach was also extended for Mn2+doping.17, 28-29 Following anion exchange with CsPbBr3 in presence of MnCl2, Mn doped mixed halides were obtained. This process slowly replaced the Br- ions in the original host nanocrystals and enhanced the Cl concentration in the same host nanocrystals (Figure 1a, Scheme –IV).16, 30 Summarizing several such reports on Mn doped perovskites, details of the reactions, obtained PLQY etc. provided in Table 1.

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Figure 1. (a) Schematic presentation of various developed synthesis strategies. (I) Represents typical high temperature synthesis using chloride salts of Pb and Mn. It also presents the increase of reaction temperature as well as Mn concentration which enhanced the doping efficiency. (II) Depicts the scheme of synthesis of Mn doped perovskites using ammonium salts at high temperature and HCl at room temperature. (III) Shows the metal chloride induced Mn doping via post synthesis of hosts. (IV) Presents the Mn doped mixed halide perovskites started with CsPbBr3 to mixed halides. (b) and (c) digital images of reaction flasks showing the yellow-orange and orange-red emissions under illumination (365 nm). Image in Figure 1b has been adopted from the reference 14 and copyrights obtained from Wiley-VCH. While most of the efficient Mn doped CsPbCl3 nanocrystals emit in yellow-orange window (~580-590 nm), tuning the compositions the emission was red tuned to orange-red region (~625 nm). This was achieved mostly by increasing the Mn content in the host lattice.19, 31 Digital image of the reaction flask having the low energy emitting Mn doped CsPbCl3

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nanocrystals under illumination is shown in Figure 1c and more on this red shifting is discussed in later section.

Figure 2. (a) Successive PL spectra of the Mn doped CsPbCl3 obtained with variation of oleylammonium chloride salts in the reaction mixture. (b) PL spectra of Mn doped CsPbCl3synthesized at different reaction temperatures. Inset shows the plot of PLQY versus reaction temperature. (c) PL spectra of Mn doped CsPbCl3 obtained on post synthesis ionexchange process. (d) PL spectra of mixed halide perovskites obtained with successive change of the halides contents. (e) PL spectra of Br- treated Mn doped CsPbCl3 nanocrystals showing optimum amount of Br- helps in obtaining intense dopant emission. Panel 2a was reprinted with permission from reference 14. Copyright was obtained from Wiley-VCH. Panel 2b, 2c, 2d and 2e were obtained with permission from references 18, 27, 28 and 17 respectively. Following the above schemes, the photoluminescence obtained from respective doped nanocrystals are presented in Figure 2. Varying the oleylammonium chloride concentrations, the change of host exciton and Mn dopant emission spectra are shown in Figure 2a. The normalized spectra at the host emission confirmed that the third material (oleylammonium chloride) indeed enhanced the intensity of dopant emission.14 This salt acted as dual source; first this provided excess chloride ions and second this also supplied adequate ammonium 6


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ions which helped for better surface passivation.24, 32 In addition, this salt also restricted the phase change of the nanocrystals and retained the cubic phase even with hours of prolonged annealing. Gamelin and co-workers18 had shown that higher reaction temperature also facilitate efficient doping. With increase of reaction temperature, they had reported the enhancement of the intensity of Mn d-d emission. Figure 2b presents the host emission normalized PL spectra of Mn doped CsPbCl3 with variations of reaction temperature and the 230 oC reaction indeed showed the most intense dopant emission. Hence, for efficient doping, reaction temperature also matters. Beyond these reports, several other strategies were also developed and one such process was cation exchange. Gao et al.33 reported the synthesis of luminescent CsPb1−xMnxCl3 nanocrystals through partial and reversible cation exchange reaction between Pb and Mn in both CsMnCl3 and CsPbCl3 nanocrystals. In an interesting approach Chen et al. showed the room temperature anion exchange induced Mn insertions in CsPbCl3nanocrystals.27 Authors performed this by using different metal chloride salts and it was established that chloride ions were the key for promoting the insertion of Mn2+ in perovskite nanocrystals for room temperature reactions. This was confirmed by using Mn-acetate (instead of MnCl2) as the Mn source and this could not help in obtaining the Mn d-d emission even after stirring for an hour at room temperature along with the host nanocrystals.27 As shown in Figure 2c, using NH4Cl, ZnCl2, GdCl3 and SnCl4, indeed prompted the cation exchange of Pb with Mn and generated the orange Mn d-d emission.27 Higher the valence of the metal in the chloride salt, better was the doping efficiency and this was related with the chloride contents in the reaction system to proportionate the Mn insertion via ion exchange. Hence, excess of chloride ions mostly facilitated the Mn2+ doping in CsPbCl3 nanocrystals.

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While all above hosts were CsPbCl3, doping of Mn2+ was also extended to mixed halide perovskites. This was performed either starting with CsPbBr3 by chloride addition16 or with Mn doped CsPbCl3 by bromide insertion.17, 28 The reaction could be started with the doped nanocrystals or the dopant Mn2+ ions might be inserted during the halide ion exchange process. Increase of chloride contents in the mixed halide perovskites helped in widening the bandgap and so also, this influenced the Mn d-d emission. A typical example of the reaction started with Mn doped CsPbCl3 is presented in Figure 2d where with Br- addition, the Mn d-d emission was slowly diminished and the exciton emission was red shifted. This was because of the enhanced Br-content in the mixed halide perovskite. The exchange rate was also observed tuned with tuning the Pb to Mn precursor content in the reaction. In another report Xu and Meijerink even stated that addition of certain amount of Br- indeed helped for enhancing the energy transfer efficiency from the host to dopant emissive states.17 The successive PL spectra with composition variation in the Br- treated Mn doped CsPbCl3nanocrystals in such a system is presented in Figure 2e. This has been established by comparing the relative PL intensity of the nanocrystals obtained during successive Br- addition. Even though the size, shape and bandgap of the hosts are suitable for transferring their exciton energy to Mn for obtaining the Mn d-d emission, did not favor the tunability of the emission energy; but with Mn2+ environment variations, the emission was observed tuned. This tunability only covered a short window and also the intensity of the emission reduced with red shifting.19, 31, 34 This has been extensively studied in chalcogenide hosts.35 This red tuning was because of the lattice contraction induced change in the crystal field strength which in turn influenced the energy gap between emissive Mn d-states. Importantly,

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Samanta and co-workers reported that similar observations could be obtained in Mn doped CsPbCl3 perovskite nanocrystals.31 In the first of its kinds in perovskite systems, they could tune the emission position from ~585 nm to ~625 nm. This was achieved by increasing the Mn content in the reaction system. Figure 3a presents the PL spectra of host CsPbCl3 and with variation of Mn insertion upto 15.5% and with rise of Mn in the composition, the Mn dd emission intensity was enhanced with suppression of high energy host emission. It is also important to mention here that Mn doped CH3NH3PbCl3 nanocrystals with an intense dopant emission at ~610 nm is also reported thereafter.50

Figure 3. (a) PL spectra of CsPbCl3 nanocrystals with various Mn contents. With increase of Mn concentration, the dopant emission is red shifted. (b) Corresponding Electron paramagnetic resonance (EPR) spectra of Mn doped CsPbCl3 nanocrystals with Mn variation. Panels of this figure are reprinted with permission from Reference 31 and copyrights obtained from Royal Society of Chemistry. For understanding the Mn distribution in the host crystals, authors carried out room temperature X-band EPR spectra of the doped nanocrystals (Figure 3b). The EPR spectra with hyperfine coupling constant, A = 86 G was observed for 1 and 2% Mn doped nanocrystals which was expected for Mn2+ confirmed Mn remained in the octahedral 9



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environment. However, with increase of Mn content, only one peak was remained and this was expected because of strong Mn-Mn coupling. From EPR data and Mn emission decay behavior it was concluded that the exchange interaction between Mn2+ ions was responsible for the red shift.

Figure 4. (a) An atomic model of L2PbBr4 where L is n-butylammonium ion. (b) Optical microscopic image of Mn doped L2PbBr4 under UV irradiation (λ= 340−380 nm). (c) PL spectra obtained with variation of Pb to Mn precursors during loading in the reaction system. Excitation wavelength is 350 nm. These microcrystals were obtained in solution phase synthesis. (d) PL spectra of Mn doped L2PbBr4 with different Mn content obtained following solid state synthesis. Panel 4a-4c and 4d were reprinted with permission from references 22 and 21 respectively. Soon after the development of 3D perovskites, emissive 2D layered perovskites were also reported36-37 and Mn2+ doping was also extended to these microstructures. The doping was successfully carried out following both solution phase and solid state synthesis. Among the layered L2PbX4 (X = Cl, Br and I) perovskites, L2PbBr4 (atomic model shown in Figure 4a) having shorter n-butylammonium ions (as L) was found as the ideal host for being able to transfer the exciton energy to the Mn d-states.21-22 Hence, efficient Mn d-d emission was observed only for L2PbBr4 though doping could be successfully achieved for L2PbCl4 and L2PbI4.22 Typical optical microscopic image of these Mn:L2PbBr4 microcrystals obtained

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under illumination is shown in Figure 4b. The PL spectra with varying the Pb to Mn precursor ratio is presented in Figure 4c which followed similar to the doping in 3D perovskites. wherein addition, with enhanced Mn2+ concentration in the host nanocrystals, the intensity of Mn d-d emission was observed improved along with the quenching of the subsequent host emission. While these microstructures were obtained in solution phase using presynthesized butylammonium bromide; similar doping observations was also reported for solid state synthesis. Kundu and co-workers in first of its kind, used the solid-state approach by grinding of L2PbBr4 and MnBr2 for obtaining the doped layered perovskites21 and the PL spectra of a typical case presented in Figure 4d which showed the intensity tuning of the host and dopant emissions with variable percentage of Mn.

Figure 5. (a) Synthesis scheme for introducing Cs(I) to layered perovskite L2PbBr4 for obtaining Mn:CsPbBr3 nanocrystals. (b) PL spectra of Mn doped CsPbBr3nanoplatelets and (c) Successive PL spectra with different HBr addition for obtaining CsPbBr3 nanocubes. (d) Successive PL spectra of different monolayers of Mn:CsPbBr3 nanoplatelets. Figure 4b-4c and 4d were reprinted and taken permissions from the references 23 and 38 respectively. Son and coworkers reported for the Mn:CsPbBr3 nanocrystals by injection of Cs precursor to the layered perovskites (L2[Pb1-xMnx]Br4, L: ligand).23 A schematic presentation of the synthesis of these nanostructures is shown in Figure 5a. These layered perovskites having

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one monolayer and Mn2+, also showed the Mn d-d emission. However, injection of Cs-oleate at high temperature (200 oC), these were transformed to Mn-doped CsPbBr3 nanocrystals as the final product. However, these doped nanocrystals contained mixture of nanocubes and thin nanoplatelets, and each species were separated via centrifugation and both showed intense Mn d-d emission. The quantum confined CsPbBr3 platelets having high bandgap performed efficient energy transfer to Mn d-states leading intense Mn dopant emission. Figure 5b shows the PL spectra of these nanoplatelets and this showed dominated Mn d-d emission. However, this doping was observed facilitated by HBr concentration. Unlike CsPbCl3 where bulk crystals could also emit Mn d-d emission, CsPbBr3 having certain size within the quantum confinement were only able to transfer the host exciton energy to Mn d-states. Hence, doped platelets and smaller size cubes could be the ideal host for obtaining this emission. This was confirmed by synthesizing different size cubes of CsPbBr3 by varying the amount of HBr and the smaller size cubes obtained with more HBr showed the intense Mn d-d emission. The observation is reflected from the PL spectra (Figure 5c) of the cubes which were obtained with HBr concentration variations in the reactions. In another report Nag et al., studied the room temperature ion exchange induced Mn doping in CsPbBr3 nanocrystals.38 Authors performed the ion exchange in different monolayers of platelets by adding MnBr2 and obtained the Mn d-d emissions. Figure 5d presents the PL spectra of three different size platelets and thinner were the platelets better was the doping efficiency. This might be explained again using the similar reason of quantum confinement as stated by Son and co-workers.23

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.

Figure 6. Digital images of hexane dispersed Mn doped CsPbCl3 nanocrystals at room temperature (RT), liquid nitrogen (LN2) temperature and during heating up from LN2 to RT. Images with dual colors signify the temperature differences in two parts of the container. The excitation wavelength is 365 nm. Even the host was changed from chalcogenides to perovskites; but the Mn d-d emission position, excited state decay lifetime and also the Mn concentration dependent emission variations remained similar. However, the most striking observation in the dopant emission properties reported was the low temperature photoluminescence. Gamelin and coworkers,18 reported that going from room temperature to liquid N2 temperature, the host exciton emission was observed enhanced similar to chalcogenide nanocrystals; but interestingly, the Mn d-d emission was found quenched. This observation was opposite to the low temperature dopant emission in chalcodenides.18, 20 However, returning back to room temperature again both emissions returned to their original position. Digital images of the 3D Mn doped perovskite nanocrystals measured at room temperature, liquid nitrogen temperature and in between during heating are presented in Figure 6. The yellow-orange color obtained at room temperature reversibly regained while heated from liquid nitrogen temperature. The plausible explanation provided for this reverse observation in compassion to doped chalcogenide was the faster recombination rate of exciton. As a result, the energy transfer from host to Mn d-states in perovskites became insufficient and this diminished the 13



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intensity of the dopant emission. This temperature dependent branching of the relaxation channel (direct exciton recombination and Mn2+ sensitization) indeed explained such reverse observations. In a different experiment for doped layered perovskites, Dutta et al., reported similar observation; but stated that in layered perovskites with increase of Mn concentration the decrease of PL intensity of dopant emission was less pronounced because of their intermediate characteristics.22 In an another interesting report by Brovelli et al., the Mn emission was observed quenched bellow 200 K; but, on further cooling beyond 70 K the Mn emission again reappeared. It was predicted that originally the excitonic energy was localized on a shallow metastable state, which was transferred to the dopant state. Bellow 200 K, the sensitization of Mn through the shallow metastable state was quenched and hence the excitonic emission was enhanced and dopant emission intensity was reduced. Further cooling bellow 70 K, the gain in dopant emission was established because for the energy transfer was directly from the band edge.39 Table 1: Synthesis Information of Selected Mn Doped Perovskite Nanocrystals. Sl Materials no 01 Mn:CsPbCl3 02 Mn:CsPbCl3 Mn:CsPb(Cl/Br)3 03 Mn:CsPbCl3 04 MAPb1−xMnxBr3−( 2x+1)Cl2x+1 05 Mn:CsPbCl3 06 Mn:CsPbCl3 07 CsPbxMn1−xClyBr3 ‑y

Mn Precursor

Pb:Mn Precursor ratio MnCl2 1:0.4 MnCl2 1:1.5 MnCl2 Mn acetate 1:0.005 MnCl2

1:9

MnCl2 MnCl2 MnCl2

1:1 1:2 1:5

08 Mn:(C4H9NH3)2Pb MnBr2

1:0.05

Synthesis Highlights

180 oC synthesis 27% 200 oC synthesis 58% 200 oC synthesis HCl added, shellgrowth Roomtemperature synthesis 190 oC synthesis 190 oC synthesis Roomtemperature synthesis Solid state

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PL QY


Research group/Refe rence Klimov12 Son13

16% 40%

Meijerink25

51%

Im40

10+/-2% Brovelli41 62% Gamelin18 40% Li42 37%

Kundu21

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Br4 09 CsPb0.88Mn0.12Cl3 MnCl2 10 CsPb0.835Mn0.165Cl MnCl2 3 11 Mn:CsPbCl3 MnCl2

grinding 1:4 1:6

170 oC synthesis 170 oC synthesis

48% 34%

Xia30 Chen28

1:1.5

54%

Chen43

12 Mn:CsPbCl3 13 Mn:CsPbCl3

MnCl2 MnCl2

1:1 1:0.05

60% 27%

Liu44 Pradhan14

14 Mn:CsPbCl3 15 Mn:CsPbCl3 platelets 16 Mn:CsPbCl3

MnCl2 MnCl2

1:0.4 1:0.05

27% 20.3%

Samanta31 Nag45

MnCl2

MnCl2

54% 5% 22% 36% 43% 17% 30%

Zhang26

17 Mn:CsPbCl3

1:10 1:2.5 1:2.5 1:10 1:5 1:10 1:1.5

Post synthesis KCl treatment 170 oC synthesis Oleylammonium chloride added, 180 oC synthesis 185 oC synthesis Room temperature 170 oC Synthesis 150 oC Synthesis 190 oC Synthesis 190 oC Synthesis 210 oC Synthesis 210 oC Synthesis 200 oC Synthesis

18 Mn:Cs2AgInCl6

Mn acetate

-

105 oC synthesis

16+/-4% Manna47

19 2D Mn:CsPbCl3

MnCl2

2:1

Solvothermal treatment

21%

Zheng48

20 CsPb0.77Mn0.23Cl3

MnCl2

1:1

160 oC synthesis

26.1%

Jung49

21 CH3NH3PbxMn1xCl3

MnCl2

1:0.75

15.2%

Luo50

22 Mn:CsPbCl3

MnCl2

1:2.5

Roomtemperature synthesis 190 oC synthesis

48%

Han51

23 Mn:CsPbCl3 24 Mn:CsPb(ClyBr1– y )3 25 Mn:CsPbBr3

MnCl2 MnCl2

1:2 1:2

150 oC synthesis Ion exchange

51.9% 59.3%

Zhao20 Xia52

MnBr2

1:5

Layer perovskite to 3D perovskite

27%

Son23

26 Platelets Mn:CsPbCl3

MnCl2

MnCl2

Layered perovskite to doped platelets Microwave assisted synthesis

33.5% 35% 36% 65%

Pradhan53

27 Mn:CsPbCl3

1:0.25 1:0.5 1:1 1:1

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He46

Yang54


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28 Mn:(Butyl)2PbBr4 MnBr2

1:1

120 oC synthesis

61%

Pradhan22

29 Mn:CsPbCl3

1:0.2

CuCl2 assisted 260 oC synthesis 100 oC synthesis

68%

Pradhan57

26%

Nag58

MnCl2

30 Mn:(butyl)2PbBr4 MnBr2

1:1.08

Summary and Future Prospects In summary, developments in the physical processes in synthesis of various Mn doped 3D and 2D layered perovskites are reported. Insights mechanism of the dopant insertions in these perovskite nanocrystals in high/room temperature synthesis and the influence of Mn concentration, presence of different metal/non-metal halide salts, reaction temperature and addition of other halide ions are discussed. Among the properties, the temperature dependent change in Mn d-d emission intensity both in 3D and 2D perovskites, Mn concentration dependent enhancing/diminishing and red tuning of the dopant emission intensity are elaborately summarized. However, even though success has been achieved in doping several perovskite nanostructures and intense dopant emission was achieved; but much more science behind doping, the physical processes involved in doping strategy and the new properties on the doped nanocrystals still remained to be investigated. Keeping the importance of these unique longer lifetime emission of doped perovskites, some of the future prospects to be investigated and the new insights involved in doping process are listed for future studies. •

Even though perovskite nanocrystals synthesis is widely established, slowing down

the growth process could not be achieved. Doping is an established concept and is mostly facilitated by adsorption and this needs a slow growth of the host. Hence, even though simultaneous presence of all precursors including Mn led to Mn d-d emission, but the placement and understanding the dopant implantation in the host lattice in unclear. Hence, 16


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precise control over the synthesis process and dopant insertion needs to be deeply investigated. Overall, how to dope the perovskite nanocrystals is still remained elusive and needs further exploration. •

Even though halide ion induced Mn insertion inside the host nanocrystals at room

temperature successfully achieved, but how do the odd ions make the process feasible is not yet understood. The ion exchange and the energy involved in these process needs to be studied for better understanding the process. •

Why does one need excess of Mn precursor even to obtain a few percentage doped

in the host perovskite nanocrystals? The Mn precursor can either supply more chloride (for MnCl2) or more Mn-ions in bulk solution. Between these two the key factor to make the insertion favorable are yet to be investigated. This would be possible only after understanding more on the fundamental insights of the doping process in these newly emerged perovskite nanocrystals. •

The magnetic properties, dopant concentration dependent Mn-Mn coupling,

presence of other optically active or magnetic dopants or making heterostructures by integrating with other semiconductors might provide new information or opens up new properties and hence, to be investigated. •

Though different strategies for improving dopant emission was reported (Table 1),

but all are accompanied with host perovskite emission, and hence there should be a search for nanocrystals with pure dopant emission. •

It is recently established that surface passivation and/or presence of halide ions can

manifold enhance the host exciton emission.24, 32, 55-56 However, their impact on the dopant emission had not yet been investigated. Ultrafast spectroscopy might provide more information of additional states and the conditions where maximum percentage of the host 17



exciton energy would be transferred to the dopant states. Hence, more spectroscopic study should be carried out. ASSOCIATED CONTENTS AUTHOR INFORMATION Contact authors email: (NP) [email protected], (AKG) [email protected] ACKNOWLEDGMENTS IACS faculty grant is acknowledged for funding. SDA acknowledge CSIR, India for fellowship. Note The authors declare no conflict of interest. REFERENCES (1)

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Insights of Doping and the Photoluminescence Properties of Mn

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