not limited to solar energy harvesting, thin film transistors, light emitting diodes, sensors, optical limiters, and wearable devices. [1] Materials with enhanced optical limiting properties are of great demand in protecting various optical devices from laser radiations. A good optical limiter is a material which allows the optical radiation to pass through at low fluences but clamps the transmitted intensity as the incident laser fluence increases. This property of materials can be useful to fabricate devices for pulse shaping, [2] passive mode locking, [3] and eye protection against powerful lasers. [4] Typically, optical limiting happens in materials is due to reverse saturable absorption or excited state absorption. When a material is illuminated with a laser beam, it can absorb the laser light even when the incident laser energy is lower than the band gap of the material by two-photon absorption (2PA). However, in a direct band gap material in which the incident laser energy is higher than the band gap, the appreciable linear absorption induces free carrier absorption. [5] In the bulk form, most of the 2D dichalcogenides are indirect-band gap materials with conduction band minimum and valence band maximum located at Q and Γ points, respectively. [6] In the monolayer regime, the dichalcogenides The advancement in high power lasers has urged the requisite of efficient optical limiting materials for both eye and sensor protection. The discovery of atomically thin 2D transition metal dichacogenides with distinctive properties has paved the way for a variety of applications including optical limiting. Until recently, the optical limiting effect exhibited by 2D materials is inferior to the benchmark materials fullerene (C 60 ) and graphene. This article reports the optical limiting activity of the 2D transition metal dichal cogenide, titanium disulfide (TiS 2 ) nanosheets, using optical and photo acoustic zscan techniques. The 77% nonlinear optical limiting exhibited by the TiS 2 sheets with 73% lineartransmittance is superior to that of any other existing 2D dichalcogenide sheets, graphene, and the benchmark optical limiting material, C 60 . The enhanced nonlinear response is attributed to the concerted effect of 2photon and the induced excited state absorp tions. By using photoacoustic zscan, a unique tool developed to determine the nonlinear optical limiting mechanism in materials, it is found that the optical limiting exhibited by TiS 2 2D sheets and graphene are mainly due to nonlinear absorption rather than scattering effects. These results have opened the door for 2Ddichalcogenidematerialsbased highly efficient optical limiters, especially at low fluences.Since the advent of graphene, 2D materials have gained considerable attention owing to their incredible electrical and optical properties. Current efforts to utilize the unique features of these materials have been focused on their integration into a vast array of electrooptical applications. These include but are [+] Present address:

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Hybrid perovskites have been investigated for various potential applications because of their tunable optical properties. In this paper, we report the synthesis of quantum dots (QDs) of two-dimensional (2D) Ruddlesden–Popper (RP) hybrid perovskite using a top-down approach. The QDs of the developed 2D RP perovskite exhibit high and sharp photoluminescence in the ultraviolet region. The sharp peak in the absorption spectrum and the intense photoluminescence in the ultraviolet region indicate strong quantum confinement in these particles, which is further confirmed by x-ray photoelectron spectroscopy. These QDs show superior nonlinear optical scattering and absorption properties with the optical z-scan technique and strong nonlinear absorption property with the photoacoustic z-scan technique. Evaluating the nonlinear optical properties using two complementary techniques provides a deeper understanding of the nonlinear mechanism involved in the optical limiting process. The two-photon absorption coefficient obtained by optical z-scan is 7.2 × 102 cm/GW, which is larger than that of most perovskite nanocrystals and nanosheets. Our studies, therefore, reveal a new class of material, 2D RP perovskite QDs, which show important nonlinear properties that are important for optical limiting applications.

A simple and facile method to synthesize nanoplatelets of 2D Ruddlesden–Popper perovskites is presented. The nanoplatelets exhibit excellent emission in the ultraviolet region and the photodetector fabricated using the nanoplatelets shows high photodetectivity.

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