1 Giant and tunable excitonic optical anisotropy in single -crystal CsPbX 3 halide perovskites

2025-04-28 0 0 1.48MB 18 页 10玖币

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Giant and tunable excitonic optical anisotropy in single-crystal

CsPbX3 halide perovskites

G.A. Ermolaev1, A.P. Pushkarev2, A.Yu. Zhizhchenko3,4, A.A. Kuchmizhak3,4, I.V. Iorsh2, I.

Kruglov,5,6, A. Mazitov5,6, A. Ishteev7,8, K. Konstantinova7, D. Saranin7, A.S. Slavich5, D. Stosic5,

E. Zhukova5, G. Tselikov1, Aldo Di Carlo7,9, A.V. Arsenin1, K.S. Novoselov10,11,12, S.V. Makarov2,

and V.S. Volkov1

1Xpanceo, Dubai Investment Park First, Dubai, UAE.

2ITMO University, School of Physics and Engineering, St. Petersburg, 197101, Russia

3Far Eastern Federal University, Vladivostok 690091, Russia

4Institute of Automation and Control Processes, Far Eastern Branch, Russian Academy of Science,

Vladivostok 690041, Russia

5Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology,

Dolgoprudny 141700, Russia.

6Dukhov Research Institute of Automatics (VNIIA), Moscow 127055, Russia.

7LASE – Laboratory of Advanced Solar Energy, NUST MISiS, 119049 Moscow, Russia

8N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences

119991, Moscow, Russia

9CHOSE – Centre of Hybrid and Organic Solar Energy, Department of Electronics Engineering,

Rome, Italy

10National Graphene Institute (NGI), University of Manchester, Manchester M13 9PL, UK.

11Institute for Functional Intelligent Materials, National University of Singapore, Singapore.

12Chongqing 2D Materials Institute, Chongqing 400714, China.

e-mail: volkov.vs@mipt.ru

ABSTRACT

During the last years, giant optical anisotropy demonstrated its paramount importance for light

manipulation which resulted in numerous applications ranging from subdiffraction light guiding

to switchable nanolasers. In spite of recent advances in the field, achieving continuous tunability

of optical anisotropy remains an outstanding challenge. Here, we present a solution to the problem

through chemical alteration of the ratio of halogen atoms (X = Br or Cl) in single-crystal CsPbX3

halide perovskites. It turns out that the anisotropy originates from an excitonic resonance in the

perovskite, which spectral position and strength are determined by the halogens composition. As

a result, we manage to continually modify the optical anisotropy by 0.14. We also discover that

the halide perovskite can demonstrate optical anisotropy up to 0.6 in the visible range – the largest

value among non-van der Waals materials. Moreover, our results reveal that this anisotropy could

be in-plane and out-of-plane, depending on perovskite shape – rectangular and square. Hence, it

can serve as an additional degree of freedom for anisotropy manipulation. As a practical

demonstration, we created perovskite anisotropic nanowaveguides and show a significant impact

of anisotropy on high-order guiding modes. These findings pave the way for halide perovskites as

a next-generation platform for tunable anisotropic photonics.

INTRODUCTION

Optical anisotropy is one of the most useful and thought after effects for modern nanophotonics.1

Aside from additional degree of freedom,2 anisotropy enables novel physical effects and

applications: extreme skin-depth guiding,3 ultrastrong coupling,4 polariton canalization,5,6

achromatic waveplates,7 switching nanolasers,8 exciton-polariton transport,3,9 lossless light

confinement,10 exceptional coupling,11 topological singularities,12 ghost13 and shear14 polaritons to

name just a few. These breakthroughs establish a quest for anisotropic materials with giant and

tunable birefringence ∆n, which describes the speed of light difference between orthogonal

directions.15 The latest studies3,16 propose the usage of van der Waals layered materials to tackle

this problem since weak binding between atoms in one of the directions naturally lead to high

birefringence. Additionally, layered structures are susceptible to atom intercalation, which is an

efficient route for anisotropy manipulation.17,18 Such methods of controlling anisotropy, however,

do not allow for continuous adjustment, resulting in a discrete number of material phases.

Furthermore, the intercalation approach has been implemented only for mid-infrared spectral range

so far,17,18 while the majority of photonic devices operate at visible frequencies.12,19,20 As a result,

tunable anisotropic optical response is in high demand.

In turn, halide perovskites is a family of materials where variation of anions in the composition

can dramatically change band gap over the whole visible range.21 In particular, the optical

properties of perovskite composition CsPbBr3-xClx can be easily tuned by HBr or HCl acids

exposure even in gas phase.21,22 More importantly, halide perovskites, for instance CsPbBr3,

exhibit orthorhombic crystal structure (Figure 1a) at room temperature,8,23,24 thus naturally having

anisotropic optical response. Surprisingly, only recent research7,8,25 paid attention to anisotropy,

while many others26,27 continue to use the isotropic treatment. This inconsistency between works

leads to a question: why anisotropy manifest itself only in limited cases. For this reason, accurate

characterization of anisotropic dielectric tensor of halide perovskites is of paramount importance

for advanced optics and perovskite applications.

In this work, we resolve this challenge and demonstrate a broadband modification of the

anisotropic optical properties of CsPbBr3-xClx through the variation of chemical atomic

composition. We found that halide perovskite anisotropy is comparable to classical birefringent

materials such as rutile and calcite at near-infrared wavelengths. Meanwhile, at exciton resonance,

anisotropy reaches much higher values, exceeding all non-van der Waals materials. Additionally,

our study shows that shape can determine the direction of optical axis and, therefore, anisotropic

tensor. As a practical demonstration, we present anisotropic waveguides based on

CsPbBr3. Remarkably, our results are applicable at all scales: nano, micro, and macro, unlike

layered materials, which to date demonstrate giant anisotropy only at the microscale. Moreover,

halide perovskites possess countless benefits: low-cost fabrication,28,29 high quantum yield of

luminescence30 and optical contrast,31 strong excitonic response,32,33 and wide composition

diversity.34,35 Therefore, the proposed tunable optical anisotropy in single-crystal CsPbX3 offers

an unprecedented platform for current and future perovskite nanophotonics and optoelectronics.

RESULTS

Optical anisotropy in halide perovskites microcrystals

Orthorhombic structure (a = 8.2563 Å, b = 8.2012 Å, c = 11.7308 Å) of halide perovskites,

presented in Figure 1a, essentially results in different optical responses along orthogonal

directions. These responses can be described by diagonal dielectric tensor diag(na,nb,nc), where na,

nb, and nc are complex refractive indices along corresponding crystallographic basis (a,b,c).

Provided that a≈b within 0.7% accuracy and, hence, na≈nb=nab, halide perovskites are basically

uniaxial crystals with dielectric tensor diag(nab,nab,nc). Our polarized microtransmittance

measurements in Supplementary Note 1 support this conclusion. To our surprise, polarized

microtransmittance also showed that rectangular-shaped microplates have in-plane anisotropy, in

contrast to square-shaped with out-of-plane anisotropy. This observation explains the

inconsistency between anisotropic and isotropic responses of halide perovskite in recent

works.7,8,25–27

In order to manipulate the crystal structure we placed CsPbBr3 microplates in HCl atmosphere

(Supplementary Note 2). HCl reacts with the crystal by substituting Br atoms with Cl atoms,

resulting in an intermediate state CsPbBr3-xClx, illustrated in Figure 1b. In this way, together with

the crystal structure, we also control the whole dielectric tensor diag(nab,nab,nc), described by two

critical parameters: refractive index nab and birefringence ∆n = nab – nc. To investigate this effect,

we leveraged imaging spectroscopic ellipsometry because it allows us detection of the optical

signal even from microplates, Figure 1c. In order to boost the signal we chose thick microplates

(Figure 1d), which demonstrate Fabry-Perot resonances. They enhance the ellipsometer

sensitivity to material anisotropy and produce characteristic asymmetric peaks in spectra.3 Besides,

we focused on microplates with out-of-plane anisotropy, which allow standard ellipsometry

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1Giantandtunableexcitonicopticalanisotropyinsingle-crystalCsPbX3halideperovskitesG.A.Ermolaev1,A.P.Pushkarev2,A.Yu.Zhizhchenko3,4,A.A.Kuchmizhak3,4,I.V.Iorsh2,I.Kruglov,5,6,A.Mazitov5,6,A.Ishteev7,8,K.Konstantinova7,D.Saranin7,A.S.Slavich5,D.Stosic5,E.Zhukova5,G.Tselikov1,AldoDiCarlo7,9,A.V.Arsenin1...

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1 Giant and tunable excitonic optical anisotropy in single -crystal CsPbX 3 halide perovskites

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