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Planar optical waveguides activated with inorganic lead-halide perovskite nanoplatelets


  Tsafrir Abir [1,2]  ,  Yehonadav Bekenstein [3]  ,  A. Paul Alivisatos [3]  ,  Tal Ellenbogen [2]  
 [1] Department of Condensed Matter Physics, School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
[2] Department of Physical Electronics, School of Electrical Engineering, Tel-Aviv University, Tel Aviv 69978, Israel
[3] Department of Chemistry, University of California, Berkeley, California 94720, United States

We experimentaly show the integration and coupling of nanoplatelets with optical waveguide, evidenced by photon emission with momenta and polarization states matching those of the guided modes.

Inorganic lead halide perovskites (LHPs) are direct bandgap semiconductors that possess attractive electro-optical properties, such as high charge-carrier mobility and small stoke shift1. A large amount of work was invested to study electro-optic properties of thin LHP films1,2, however in recent years there has been great interest also in colloidal LHP nanocrystals (NCs). It was shown that the emission from LHP NCs is tunable over the entire visible range, while the LHPs’ native defect tolerance allows high quantum yield without the need for electronic surface passivation2. Here we demonstrate how the integration of CsPbBr3 nanoplatelets3 (NPs) in a polymer made planar waveguide (WG) results in coupling of the NCs’ excitons to the optical guided modes.

The WG was fabricated by spin-casting a mixed solution of NCs and polymer on a thin silver layer. The polymer that has been used is poly(styrene-ethylene-butylene-styrene) (SEBS) serves both as the dielectric slab forming the WG and to protect the NCs against moisture and oxidation4. Excitation of the NPs resulted in emission outflow from the sample at specific angles. Comparison between the measured reflection to the emission spectra, reveals that emission occurs at angles in which the guided modes overlap with the NPs’ emission. The NPs’ excitons’ not only preferably emit photons with momenta matching that of the guided modes, the emission becomes polarized according to WG modes’ polarizations.

These results indicate that coupling of the LHP NCs’ excitons to optical guided modes can be achieved in a relatively simple and scalable method. Therefore, control of the WG modes can be used to control the electro-optic properties of the coupled system. This can be used for development of LHP NC waveguide based electro-optical devices, such as light emitting diodes, lasers and detectors.

References

1 B. R. Sutherland and E. H. Sargent, “Perovskite photonic sources,” Nat. Photonics, vol. 10, no. 5, pp. 295–302, 2016.

2 Kovalenko, M. V, Protesescu, L. & Bodnarchuk, M. I., “Properties and potential optoelectronic applications of lead halide perovskite nanocrystals” Science,  vol. 358, no. 6364, pp. 745–750, 2017.

3 Y. Bekenstein, B. A. Koscher, S. W. Eaton, P. Yang, and A. P. Alivisatos, “Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies,” J. Am. Chem. Soc., vol. 137, no. 51, pp. 16008–16011, 2015.

4 S. N. Raja, Y. Bekenstein, M. A. Koc, S. Fischer, D. Zhang, L. Lin, R. O. Ritchie, P. Yang, and A. P. Alivisatos, “Encapsulation of Perovskite Nanocrystals into Macroscale Polymer Matrices: Enhanced Stability and Polarization,” ACS Appl. Mater. Interfaces, vol. 8, no. 51, pp. 35523–35533, 2016.