1

Supporting Information

Bright Luminescence from Nontoxic CsCu2X3 (X

= Cl, Br, I) Rachel Roccanova,1‡ Aymen Yangui,1‡ Gijun Seo,2 Tielyr D. Creason,1 Yuntao Wu,3,4 Do Young

Kim,2 Mao-Hua Du,5 Bayrammurad Saparov1*

1Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway,

Norman, OK 73019, USA

2School of Materials Science and Engineering, Oklahoma State University-Tulsa, 526 N. Elgin

Ave, Tulsa, OK 74106, USA

3Synthetic Crystal Research Center, Shanghai Institute of Ceramics, Chinese Academy of

Sciences, Shanghai, 201800, China

4Scintillation Materials Research Center and Department of Materials Science and Engineering,

University of Tennessee, Knoxville, Tennessee, 37996, USA

5Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN

37831, USA

Corresponding Author: *E-mail: saparov@ou.edu

‡These authors contributed equally to this work

2

EXPERIMANTAL METHODS

Reactants. Chemicals utilized in this study were used as purchased: (i) copper (I) chloride,

99.99%, Acros Orcganics; (ii) copper(I) bromide, 99.999%, Aldrich; (iii) copper iodide, 99.9%,

Aldrich; (iv) cesium chloride, 99.99%, Acros Organics; (v) cesium bromide, 99.9%, Acros

Organics; (vi) cesium iodide, 99.999%, Acros Organics.

Synthesis of CsCu2X3 (X = Cl, Br, I). Crystalline ingots were prepared using a 1:2 stoichiometric

ratio of CsX to CuX (X = I, Br, Cl) ground in an agate mortar, pelletized and sealed under dynamic

vacuum in quartz ampules. Pelletized samples were annealed at 410 °C for 48 hours and slowly

cooled over 20 hours to room temperature resulting in polycrystalline ingots.

Powder X-ray Diffraction. Powder X-ray diffraction (PXRD) measurements were performed on

a Rigaku MiniFlex600 system equipped with a Dtex detector using a Ni-filtered Cu-Kα radiation

source. All scans were performed at room temperature from the 5-90˚ (2θ) range, with a step size

of 0.2˚. All data were corrected for the amorphous background of the glass slides used during

collection and fitted using the Pawley method through Rigaku’s PDXL2 software package. To

check the air stability, samples were left in ambient air for more than two months with periodic

PXRD measurements using the same condition mentioned above.

Thermal Analysis. Simultaneous thermogravimetric analysis (TGA) and differential scanning

calorimetry (DSC) measurements were carried out on a TA Instruments SDT650 unit.

Measurements were performed using 90 µL alumina crucibles on 8-10 mg samples under a 100

mL/min flow of dry nitrogen in the 100–575 °C range with 5 °C/min heating rate.

Optical Measurements. Room temperature diffuse reflectance spectra of polycrystalline powder

of CsCu2X3 of were measured using a high-resolution PerkinElmer LAMBDA 750 UV−vis−NIR

spectrometer equipped with a 100 mm InGaAs integrating sphere attachment. The diffuse

3

reflectance data were converted to pseudoabsorption spectra according to the the Kubelka-Munk

equation:1 (F(R) = α/S = (1-R)2/(2R), where R is the reflectance, α is the absorption coefficient, S

is the scattering coefficient.

Photoluminescence excitation (PLE), and photoluminescence quantum yield (PLQY)

measurements were performed at ambient temperature, on polycrystalline powder samples, using

a HORIBA Jobin Yvon Fluorolog-3 spectrofluorometer equipped with a Xenon lamp and Quanta-

φ integrating sphere. PLQY data were analyzed using the two-curve method in a varied range from

280 – 800 nm using the imbedded QY software in the Horiba-Jobin Yvon software.

Time resolved photoluminescence (TRPL) measurements were done on polycrystalline powder

samples using a HORIBA Jobin Yvon Fluorolog-3 spectrofluorometer equipped with a time-

correlated single photon counting module. HORIBA Jobin Yvon NanoLEDs (pulsed light-emitting

diodes) were used as the excitation source. The duration of the light pulse was shorter than 2 ns.

Temperature and power dependence PL spectra were measured using a Princeton Instruments

PIXIS-eXcelon silicon CCD. The excitation wavelength was the 325 nm (3.815 eV) line of a He-

Cd laser (Kimmon Electric HeCd dual-wavelength laser; model: IK552R-F). The samples were

placed in a helium bath cryostat, and the measurements were performed between 4 and 295 K.

In depth structural analysis. Isolation of the copper halide tetrahedra as ribbons can be seen most

prominently down the b and c axis (as shown in Figure 1(b-c)) where the Cs+ cations fill in the

channels separating [Cu2X3]- “nanowires.” which greatly impacts the observed luminescence in

this family. The Cu-X bond distances in the [Cu2X3]- chains vary from 2.272 to 2.490 Å for

CsCu2Cl3, 2.427 to 2.571 Å for CsCu2Br3, and 2.604 to 2.703 Å for CsCu2I3, following the

expected trend based on the increasing halide ionic radii going down the group. Noticeable

distortions of the CuX4 tetrahedra are evident from the tetrahedral angles (X-Cu-X) of 102.45 to

4

119.31º, 106.41 to 116.48º, and 107.1 to 114.24º for X = Cl, Br, and I, respectively. Interestingly,

a trend of decreasing tetrahedral distortions going down the group is observed in this series.

In octahedral systems, connectivity and magnitude of distortion are known to affect the band

structure, emission properties, and defect formation within a perovskite lattice and are evaluated

using the bond lengths and angles between the metals and halides and the volume of the individual

octahedra.2 Deviation from ideal octahedral geometry results in an increase in distortion within a

perovskite system and has been shown to negatively affect the overlap between the orbitals of the

metal and halides resulting in wider band gaps and blue shifting the onset of absorption,3 as well

as decreasing the PLQY and lifetime due to an increase in the reduced mass of excitons within the

system.4 Among the quantitative methods used to determine the magnitude of distortion within a

perovskite system, the variation in octahedral distance (Δd),5 angle (σ2oct),6 and the overall

octahedral elongation (<λoct>)6 have been used in particular to relate increase in distortion with

increased Stokes-shifts, full width at half maximums (FWHMs), and broad white-light emission

caused by the self-trapping of carriers resulting from strong exciton-phonon coupling.7-10 Such

broadband luminescence is commonly seen in alkali halides,10-11 hybrid organic-inorganic

materials,9, 12-19 and recently in all-inorganic metal halides such as A3M2I9 (A = Cs, Rb; M = Bi,

Sb),20 CsZnCl2I,21 (C8NH12)4Bi0.57Sb0.43Br7,22 and Cs2AgInCl6.23 To correlate the optical properties

of the CsCu2X3 systems with that of other octahedral systems, attempts were made to relate the

calculated tetrahedral distortion to the optical properties reported below. The effect of tetrahedral

distortion on optoelectronic properties in solid-state structures have been rarely studied with no

reports comparing the magnitude of distortion to the observed properties, like in many octahedral

systems. Robinson et al. were the first to propose quantitative tetrahedral distortion parameters

that directly correlated to their proposed octahedral parameters σ2oct and λoct, allowing for the

5

comparison of the amount of distortion present in completely different polyhedra-based systems.6

Using this method, we calculated the σ2tet and <λtet> values for CsCu2X3 and found that the

distortion from both σ2tet and <λtet> decrease from CsCu2Cl3 to CsCu2I3. Typically four parameters,

variation in angle (σ2, ΔθXMX) and bond distance (<λ>, Δd) have been used to quantify octahedral

distortion through the differences in bond distances and angles, respectively.6, 24 In an attempt to

relate the observed luminescence of CsCu2X3 to the structural distortions observed in these

compounds, we performed similar distortion analysis adopted for the tetrahedral geometry. The

tetrahedral angle variance (σ2tet) and the average tetrahedral elongation <λtet> are given by the

following equations:6

𝜎𝜃 (𝑡𝑒𝑡)2 =

1

5∑(𝜃𝑡 − 109.47°)2

5

𝑖=1

⟨𝜆𝑡𝑒𝑡⟩ =1

4∑ (

𝑙𝑖

𝑙0)

24

𝑖=1

where σ2tet is deviation in bond angle of the system, θtet is the individual tetrahedral angles between

the center metal and each adjacent ligand, <λtet> is the overall octahedral elongation, li is the

measured distance between the metal center and each ligand, and l0 is the ideal bond distance

determined from the ionic radii.

Only octahedral Δd and ΔθXMX relationships have been previously reported, however, they can

be adapted for tetrahedral systems via the following equations:

∆𝑑 = 1

4∑ (

𝑑𝑛 − 𝑑

𝑑)

2

𝑛=1,4

6

∆𝜃𝑋𝑀𝑋 = 1

6∑ (

𝜃𝑋𝑀𝑋(𝑛) − ⟨𝜃⟩

⟨𝜃⟩)

𝑛=1,6

2

where Δd is one fourth of the summation of each difference of each individual bond distance

(dn) the average bond distance (d) of the tetrahedra in question squared, and ΔθXMX is one sixth of

the summation of the absolute value of the difference of each individual angle (θXMX(n)) and the

average angle of the tetrahedra in question ⟨𝜃⟩ squared. The results of these analyses are

summarized in Table S2. Confirming the noticeable trend observed for bond angles, σ2tet, <λtet>,

Δd, and ΔθXMX all suggest decreasing tetrahedral distortion from CsCu2Cl3to CsCu2Br3 to

CsCu2I3This trend is opposite of what would be expected if one only considers the increase in

atomic radii from Cl to I. However, this opposite trend has been previously reported in the

tetrahedral-based (SC(NH2))2CdX2 system,25 and 2D octahedral-based system

((CH3)2NC6H4NH3)PbX4 (X = Br, I).26 For CsCu2X3, as shown in Table 1, the Stokes-shift

increases from 208 to 249 nm and the FWHM of the broadband emission increases from 102 and

200 nm, going from for CsCu2Cl3, to CsCu2I3, which is typically due to increasing distortion within

octahedral systems.7-10, 12-18

Device fabrication. LED fabrication was attempted based on CsCu2X3 (Figure S11). In order to

fabricate LEDs, a CsCu2I3 was used as a yellow additive in an 1,3-Bis(N-carbazolyl)benzene

(mCP) host layer. LEDs were fabricated on patterned indium tin oxide (ITO) glass substrates. An

ITO was used as a transparent bottom anode. The substrates were first cleaned with acetone and

isopropanol in an ultrasonic cleaner and subsequently rinsed with de-ionized water, blown dry with

N2 gas, and treated with UV ozone. A MoO3 and a 4,4′-Cyclohexylidenebis[N,N-bis(4-

methylphenyl)benzenamine] (TAPC) were used as a hole injection layer and a hole transport layer,

respectively. CsCu2I3 (10 vol. %) doped in mCP host was used as a yellow emission layer. A 1,3,5-

7

tri (m-pyrid-3-yl-phenyl) - benzene (TmTyPB) and a LiF were used as an electron transport layer

and the electron injection layer, respectively. An Al was used as a top reflective cathode. All layers

were deposited sequentially by vacuum thermal evaporation at a pressure of 10-6 Torr. The area of

the device was 4 mm2.

Computational Methods. Density functional theory calculations were performed using the VASP

code.27 The interaction between ions and electrons was described by projector augmented wave

method.28 The valence wavefunctions were expanded in a plane-wave basis with a cut-off energy

of 369 eV. All atoms were relaxed to minimize the Feynman-Hellmann forces to below 0.02 eV/Å.

The electronic band structure and the density of states were calculated based on

Perdew−Burke−Ernzerhof (PBE) exchange-correlation functional.29 The band gap was further

corrected by the hybrid PBE0 functional.30

8

Figure S1. Room temperature powder X-ray diffraction (PXRD) patterns (black lines) for (a)

CsCu2Cl3, (b) CsCu2Br3, (c) CsCu2I3. Pawley fits of the data are shown in red and difference

plots shown in blue. In CsCu2Cl3 samples, a CsCl impurity peak (marked with a green asterisk)

is noticeable.

9

Figure S2. Room temperature powder X-ray diffraction (PXRD) patterns (black lines) for (a)

CsCu2Cl1.5Br1.5, and (b) CsCu2Br1.5I1.5. In our CsCu2Cl1.5Br1.5 sample, unassigned impurity peaks

totaling 5.4% based on intensity ratios are marked by green asterisks.

10

Figure S3. (a-c) PXRD refined lattice parameters, and (d) unit cell volume shown as a function of

halide content as alloying progresses from CsCu2Cl3 (Cl) to CsCu2Br3 (Br) to CsCu2I3 (I).

11

Figure S4. PXRD patterns of (a) CsCu2Cl3, (b) CsCu2Br3, and (c) CsCu2I3 left out in ambient

conditions and measured over a period of 2 months.

12

Figure S5. Tandem differential scanning calorimetry (red) and thermal gravimetric analysis (blue)

of (a) CsCu2Cl3, (b) CsCu2Br3, and (c) CsCu2I3.

13

Figure S6. (a) Kubelka-Munk plots of diffuse reflectance for CsCu2X3 and mixed-halide alloys

with (b-c) estimated band gap fittings.

14

Figure S7. (a) Band structure and (b) density-of-states (DOS) plots for CsCu2Cl3 calculated

using the DFT-PBE method. Note that the band gap is underestimated.

15

Figure S8. Normalized PLE spectra of CsCu2I3 measured for different emission wavelengths.

16

Figure S9. Power dependence of PL spectra for CsCu2X3 measured at 4 K under 325 nm

excitation. Black curves shows the fitting using y ~ Pk, with y, P, and k are the PL intensity, the

excitation power, and the refinement coefficient, respectively.31

17

Figure S10. Temperature dependence of PL for (a) CsCu2Cl1.5Br1.5, (b) CsCu2Br3, (c)

CsCu2Br1.5I1.5, and (d) CsCu2I3 under 325 nm irradiation. CsCu2Cl3 is shown in the main text in

Figure 4.

18

0 2 4 6 810-8

10-6

10-4

10-2

100

102

Voltage (V)

Cu

rren

t D

en

sit

y (

mA

/cm

2)

(a)

10-1

100

101

102

Lu

min

an

ce (

cd

/m2)

0.1 1 1010-3

10-2

10-1

100

Al

LiF

TmPyPb

mCP:CsCu2I3

TAPC

MoO3

ITO

(b)

Luminance (cd/m2)

Qu

an

tum

Eff

icie

ncy (

%)

400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

(c)

EL

In

ten

sit

y (

a.u

.)

Wavelength (nm)

CsCu2I3

PeakEL=554nm

FWHM=136nm

Figure S11. Light-emitting diode (LED) fabricated using CsCu2I3 as an additive in a mCP host.

(a) Luminance-current-voltage (LIV) characteristics, (b) quantum efficiency (inset: the device

structure), and (c) electroluminescence (EL) spectrum (inset: a photo image of the LED

operating at 8 V) of the LED.

19

Table S1. Summary of lattice constants from Pawley fits of the PXRD data for CsCu2X3.

Composition a (Å) b (Å) c (Å) V (Å3)

CsCu2Cl3 9.4925(2) 11.8780(2) 5.5935(2) 630.67(2)

CsCu2Cl1.5Br1.5 9.5541(9) 12.2059(11) 5.7218(5) 667.27(11)

CsCu2Br3 9.866(2) 12.348(7) 5.816(5) 708.6(5)

CsCu2Br1.5I1.5 9.9424(7) 12.9562(9) 5.9935(4) 772.06(9)

CsCu2I3 10.545(2) 13.173(9) 6.099(9) 847.4(1)

20

Table S2. Selected interatomic distances (Å) and angles (°) in CsCu2X3 based on the

crystallographic data reported in literature.32-34

Label Distance (Å) Label Angle (°)

CsCu2Cl3

Cu - Cl1 2.490(1) Cl1-Cu-Cl2 119.30(9)

Cl2 2.272(8) Cl1-Cu-Cl3 107.33(5)

Cl3 2.273(0) Cl1-Cu-Cl4 109.49(2)

Cl4 2.490(4) Cl2-Cu-Cl3 109.49(2)

Cl3-Cu-Cl4 102.44(9)

Cl2-Cu-Cl4 119.30(9)

CsCu2Br3

Cu - Br1 2.570(8) Br1-Cu-Br2 106.41(4)

Br2 2.427(0) Br1-Cu-Br3 108.15(5)

Br3 2.427(0) Br1-Cu-Br4 108.61(0)

Br4 2.571(4) Br2-Cu-Br3 108.61(0)

Br3-Cu-Br4 116.48(2)

Br2-Cu-Br4 106.41(4)

CsCu2I3

Cu - I1 2.703(4) I1-Cu-I2 109.80(1)

I2 2.604(2) I1-Cu-I3 107.10(2)

I3 2.604(2) I1-Cu-I4 108.91(0)

I4 2.703(0) I2-Cu-I3 114.24(4)

I3-Cu-I4 114.24(4)

I2-Cu-I4 109.80(1)

21

Table S3. Results of the tetrahedral distortion evaluation showing a linear decrease in distortion

with increase in halogen size.

CsCu2Cl3 CsCu2Br3 CsCu2I3

σ(tet)2 49.49 14.22 10.33

<λtet> 0.9785 0.9537 0.8984

Δd 21.67 x 10-4 13.59 x 10-4 3.05 x 10-4

ΔθXMX 68.84 x 10-4 19.44 x 10-4 14.37 x 10-4

Table S4. Summary of the time-resolved PL refinement results for CsCu2X3.

Sample CsCu2Cl3 CsCu2Cl1.5Br1.5 CsCu2Br3 CsCu2Br1.5I1.5 CsCu2I3

Excitation

(nm)

314 333 314 333 333

Emission

(nm)

527 587 533 584 576

I0 152.5 ± 0.6 85 ± 0.5 49.9 ± 0.27 15.2 ± 0.5 35.2 ± 0.7

A1 8.8 1022 ± 6.4

1022

1.5 1030 ± 7.2

1029

7.7 1024 ± 3

1024

2.9 103 ± 241 5.7 103 ± 1.3

102

𝛕𝟏 (ns) 2.1 ± 0.04 1.6 ± 0.02 1.9 ± 0.01 72.2 ± 1.7 62± 2

A2 6.4 104 ± 5.7

104

3.9 104 ± 2 104 2.3 104 ± 3.2

102

4.2 104 ± 2.6

103

356 ± 197

𝛕𝟐 (ns) 13.8 ± 0.6 15.1 ± 1.1 18 ± 0.01 26.6 ± 0.7 126.5 ± 20

Table S5. Temperature-dependent PL refinement for CsCu2X3.

Sample CsCu2Cl3 CsCu2Cl1.5Br1.5 CsCu2Br3 CsCu2Br1.5I1.5 CsCu2I3

𝚪𝐀𝐂 (meV.K-1) 0.05 ± 0.01 0.02 ± 0.008 0.3 ± 0.04 0.18 ± 0.04 027 ± 0.01

𝚪𝐋𝐎 (meV.K-1) 471 ± 13 712 ± 32 512 ± 62 910 ± 42 617 ± 22

𝑬𝐋𝐎 (meV) 6.4 ± 0.3 6.2 ± 0.6 5.1 ± 0.2 11.5 ± 0.2 4.3± 0.3

22

References

1. Kortüm, G.; Braun, W.; Herzog, G., Principles and Techniques of Diffuse-Reflectance

Spectroscopy. Angew. Chem. Int. Ed. 1963, 2, 333-341.

2. Cortecchia, D.; Yin, J.; Petrozza, A.; Soci, C., White light emission in low-dimensional

perovskites. J. Mater. Chem. 2019, 7, 4956-4969.

3. Knutson, J. L.; Martin, J. D.; Mitzi, D. B., Tuning the Band Gap in Hybrid Tin Iodide

Perovskite Semiconductors Using Structural Templating. Inorg. Chem. 2005, 44, 4699-4705.

4. Kawano, N.; Koshimizu, M.; Sun, Y.; Yahaba, N.; Fujimoto, Y.; Yanagida, T.; Asai, K.,

Effects of Organic Moieties on Luminescence Properties of Organic–Inorganic Layered

Perovskite-Type Compounds. J. Phys. Chem. C. 2014, 118, 9101-9106.

5. Lufaso, M. W.; Woodward, P. M., Jahn-Teller distortions, cation ordering and octahedral

tilting in perovskites. Acta Cryst. B. 2004, 60, 10-20.

6. Robinson, K.; Gibbs, G.; Ribbe, P., Quadratic elongation: a quantitative measure of

distortion in coordination polyhedra. Science. 1971, 172, 567-570.

7. Smith, M. D.; Jaffe, A.; Dohner, E. R.; Lindenberg, A. M.; Karunadasa, H. I., Structural

Origins of Broadband Emission from Layered Pb–Br Hybrid Perovskites. Chem. Sci. 2017,

8, 4497-4504.

8. Hu, T.; Smith, M. D.; Dohner, E. R.; Sher, M.-J.; Wu, X.; Trinh, M. T.; Fisher, A.; Corbett,

J.; Zhu, X. Y.; Karunadasa, H. I.; Lindenberg, A. M., Mechanism for Broadband White-Light

Emission from Two-Dimensional (110) Hybrid Perovskites. J. Phys. Chem. Lett. 2016, 7,

2258-2263.

9. Yangui, A.; Pillet, S.; Lusson, A.; Bendeif, E. E.; Triki, S.; Abid, Y.; Boukheddaden, K.,

Control of the White-Light Emission in the Mixed Two-Dimensional Hybrid Perovskites

(C6H11NH3)2[PbBr4–xIx]. J. Alloys Compd. 2017, 699, 1122-1133.

10. Mott, N. F.; Stoneham, A. M., The lifetime of electrons, holes and excitons before self-

trapping. J. Phys. C: Solid State Phys. 1977, 10, 3391-3398.

11. Purdy, A. E.; Murray, R. B.; Song, K. S.; Stoneham, A. M., Studies of self-trapped exciton

luminescence in KCl. Phys. Rev. B. 1977, 15, 2170-2176.

12. Smith, M. D.; Karunadasa, H. I., White-Light Emission from Layered Halide Perovskites.

Acc. Chem. Res. 2018, 51, 619-627.

13. Yangui, A.; Garrot, D.; Lauret, J. S.; Lusson, A.; Bouchez, G.; Deleporte, E.; Pillet, S.;

Bendeif, E. E.; Castro, M.; Triki, S.; et al., Optical Investigation of Broadband White-Light

Emission in Self-Assembled Organic–Inorganic Perovskite (C6H11NH3)2PbBr4. J. Phys.

Chem. C 2015, 119, 23638-23647.

14. Roccanova, R.; Houck, M.; Yangui, A.; Han, D.; Shi, H.; Wu, Y.; Glatzhofer, D. T.; Powell,

D. R.; Chen, S.; Fourati, et al., Broadband Emission in Hybrid Organic–Inorganic Halides

of Group 12 Metals. ACS Omega. 2018, 3, 18791-18802.

15. Yangui, A.; Pillet, S.; Bendeif, E.-E.; Lusson, A.; Triki, S.; Abid, Y.; Boukheddaden, K.,

Broadband Emission in a New Two-Dimensional Cd-Based Hybrid Perovskite. ACS

Photonics. 2018, 5, 1599-1611.

16. Yu, J.; Kong, J.; Hao, W.; Guo, X.; He, H.; Leow, W. R.; Liu, Z.; Cai, P.; Qian, G.; Li, S.;

Chen, X.; Chen, X., Broadband Extrinsic Self-Trapped Exciton Emission in Sn-Doped 2D

Lead-Halide Perovskites. Adv. Mater. 2019, 31, 1806385.

17. Gautier, R.; Massuyeau, F.; Galnon, G.; Paris, M., Lead Halide Post-Perovskite-Type Chains

for High-Efficiency White-Light Emission. Adv. Mater. 2019, 31, 1807383.

23

18. Lin, H.; Zhou, C.; Neu, J.; Zhou, Y.; Han, D.; Chen, S.; Worku, M.; Chaaban, M.; Lee, S.;

Berkwits, E.; et al., Bulk Assembly of Corrugated 1D Metal Halides with Broadband Yellow

Emission. Adv. Opt. Mater. 2019, 7, 1801474.

19. Yangui, A.; Roccanova, R.; McWhorter, T. M.; Wu, Y.; Du, M.-H.; Saparov, B., Hybrid

Organic–Inorganic Halides (C5H7N2)2MBr4 (M = Hg, Zn) with High Color Rendering Index

and High-Efficiency White-Light Emission. Chem. Mater. 2019, 31, 2983-2991.

20. McCall, K. M.; Stoumpos, C. C.; Kostina, S. S.; Kanatzidis, M. G.; Wessels, B. W., Strong

Electron–Phonon Coupling and Self-Trapped Excitons in the Defect Halide Perovskites

A3M2I9 (A = Cs, Rb; M = Bi, Sb). Chem. Mater. 2017, 29, 4129-4145.

21. Aamir, M.; Khan, M. D.; Sher, M.; Revaprasadu, N.; Malik, M. A.; Akhtar, J., Broadband

emission in a new lead free all-inorganic 3D CsZnCl2I perovskite. New J. Chem. 2018, 42,

17181-17184.

22. Zhang, R.; Mao, X.; Yang, Y.; Yang, S.; Zhao, W.; Wumaier, T.; Wei, D.; Deng, W.; Han,

K., Air-Stable, Lead-Free Zero-Dimensional Mixed Bismuth-Antimony Perovskite Single

Crystals with Ultra-broadband Emission. Angew. Chem. 2019, 131, 2751-2755.

23. Luo, J.; Wang, X.; Li, S.; Liu, J.; Guo, Y.; Niu, G.; Yao, L.; Fu, Y.; Gao, L.; Dong, et al.,

Efficient and stable emission of warm-white light from lead-free halide double perovskites.

Nature 2018, 563, 541-545.

24. Lufaso, M. W.; Woodward, P. M., Jahn–Teller distortions, cation ordering and octahedral

tilting in perovskites. Acta Crystallogr. Sect. B: Struct. Sci. 2004, 60, 10-20.

25. Marcos, C.; Alia, J.; Adovasio, V.; Prieto, M.; García-Granda, S., Bis (thiourea) cadmium

Halides. Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 1998, 54, 1225-1229.

26. Hautzinger, M. P.; Dai, J.; Ji, Y.; Fu, Y.; Chen, J.; Guzei, I. A.; Wright, J. C.; Li, Y.; Jin, S.,

Two-Dimensional Lead Halide Perovskites Templated by a Conjugated Asymmetric

Diammonium. Inorg. Chem. 2017, 56, 14991-14998.

27. Kresse, G.; Furthmüller, J., Efficiency of ab-initio total energy calculations for metals and

semiconductors using a plane-wave basis set. Computat. Mater. Sci. 1996, 6, 15-50.

28. Kresse, G.; Joubert, D., From ultrasoft pseudopotentials to the projector augmented-wave

method. Phys. Rev. B. 1999, 59, 1758.

29. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized gradient approximation made simple.

Phys. Rev. Lett. 1996, 77, 3865.

30. Perdew, J. P.; Emzerhof, M.; Burke, K., Rationale for mixing exact exchange with density

functional approximations. J. Chem. Phys. 1996, 105, 9982-9985.

31. Shibata, H.; Sakai, M.; Yamada, A.; Matsubara, K.; Sakurai, K.; Tampo, H.; Ishizuka, S.;

Kim, K.-K.; Niki, S., Excitation-power dependence of free exciton photoluminescence of

semiconductors. Jpn. J. Appl. Phys. 2005, 44, 6113.

32. Brink, C.; Binnendijk, N.; Van de Linde, J., The crystal structures of CsCu2Cl3 and CsAg2I3.

Acta Crystallogr. 1954, 7, 176-180.

33. Meyer, G., Synproportionierung am metallischen Substrat: CsCu2Cl3 und CsCu2Br3. Z.

Anorg. Allg. Chem. 1984, 515, 127-132.

34. Jouini, N.; Guen, L.; Tournoux, M., Structure cristalline de CsCu2I3. Rev. Chim. Mineral

1980, 17, 486-491.