We report the broadband nonlinear optical (NLO) properties of CsPbBr perovskite films achieved from colloidal nanocrystals prepared following a room temperature and open atmosphere anti-solvent precipitation method. The NLO studies were performed on the films of nanocubes (NCs) and nanorods (NRs) using the Z-scan technique with 1 kHz femtosecond pulses at 600, 700, and 800 nm. Large two-photon absorption cross sections (∼10 GM) were retrieved by fitting the open-aperture Z-scan data. Strong third-order NLO susceptibility (∼10 esu) was observed in these films. At higher peak intensities a switching of sign (in both NCs and NRs) in the real and imaginary parts of the NLO susceptibility was observed from the studies on these CsPbBr nanocrystals. The obtained NLO coefficients clearly suggest that these materials are promising for ultrafast photonic applications.

While the unabated race persists in achieving record efficiencies in solar cells and other photonic/optoelectronic devices using lead halide perovskite absorbers, a comprehensive picture of the correlated third-order nonlinear optical (NLO) properties is yet to be established. The present study is aimed at deciphering the role of dopants in multiphoton absorption properties of intentionally engineered CsPbBr 3 colloidal nanocrystals (NCs). The charge separation of the plasmonsemiconductor conduction band owing to the hot electron transfer at the interface was demystified using the dynamics of the bleached spectral data from femtosecond (fs) transient absorption spectroscopy with broadband capabilities. The NLO properties studied through the fs Z-scan technique revealed that Ni-doped CsPbBr 3 NCs exhibited strong third-order NLO susceptibility of ∼10 −10 esu. The exotic photophysical phenomena in these pristine and Ni-doped CsPbBr 3 colloidal twodimensional (2D) NCs reported herein are believed to provide the avenues to address the critical variables involved in the structural differences and their correlated optoelectronic properties.

A comprehensive investigation is presented on the photophysical and third-order nonlinear optical (NLO) properties of two thioalkyl-substituted tetrathiafulvalene molecules (referred here as G1 and G3) to understand their utility as photosensitizers for dyesensitized solar cell (DSSC) and optoelectronic applications. Both steady-state and time-resolved (in the fs−ns time regime) absorption and photoluminescence (PL) spectroscopy techniques were employed to comprehend the excited-state properties of the molecules in solution as well as in thin films deposited on both quartz and mesoporous TiO 2 layers. The spectroscopy measurements in solution and thin films deposited on quartz provided the excited-state properties of dye molecules. Time-resolved PL measurements at the dye−TiO 2 interface provided initial evidence of electron injection by fast PL quenching decay dynamics for both the molecules. Detailed target analysis of the femtosecond transient absorption spectroscopy (TAS) data of the dye−TiO 2 sample revealed a multistep ultrafast electron injection for both molecules with the fastest injection component being 374 and 314 fs for G1 and G3 molecules, respectively. The ultrafast NLO properties of G1 and G3 were studied using the Z-scan technique with 800 nm, ∼70 fs laser pulses. The open aperture measurements showed three-photon absorption with magnitudes of coefficients 4.7 × 10 −5 cm 3 /GW 2 and 5.2 × 10 −5 cm 3 /GW 2 , and the closed aperture measurements provided second hyperpolarizability (γ) values of 3.5 × 10 −31 esu and 4.2 × 10 −31 esu for G1 and G3, respectively. Additionally, the onset of optical limiting was estimated to be 5.8 × 10 −3 J/cm 2 and 5.7 × 10 −3 J/cm 2 for G1 and G3 molecules, respectively.

Structural and optical properties of antimony-containing sodium borate glasses were studied and their ultrafast third-order nonlinear optical (NLO) properties have been evaluated using Z-scan measurements with femtosecond (fs) pulses (∼150 fs, 80 MHz) at 750, 800, and 880 nm wavelengths. Glasses in the (mol %) 20Na 2 O−(80 − x)B 2 O 3 −xSb 2 O 3 (where x = 0, 10, 20, and 30) system have been fabricated via melt quench technique. The structural modifications were analyzed using the Raman and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) ( 11 B MAS-NMR and 23 Na MAS-NMR) techniques. The optical absorption spectra revealed that the absorption edge was red-shifted, suggesting the decrease in band gap energy with increase of antimony content in the glasses. Raman scattering results revealed that the boroxol rings are depressed with the incorporation of Sb 2 O 3 for replacing B 2 O 3 . 11 B MAS-NMR results showed a progressive increase of B 4 units at the expense of B 3 units. The Raman and 11 B MAS-NMR results support the formation of Sb 5+ ions due to oxidation of Sb 3+ that played the role of charge compensation. 23 Na MAS-NMR spectra revealed a decreasing trend in the average of bond lengths of Na−O with increasing Sb 2 O 3 contents. This suggested that sodium changed its role from charge compensator to modifier cation. The antimony-containing glasses demonstrated a reverse saturable absorption in open-aperture Z-scan mode due to two-photon absorption, while closed-aperture Z-scan signatures depicted positive nonlinear refraction due to self-focusing effect. The NLO coefficients were found to increase with Sb 2 O 3 due to the increased nonbridging oxygens and also due to the hyperpolarizability of Sb 3+ and Sb 5+ ions. The observed NLO data clearly suggest that the investigated glasses are beneficial for optical limiting applications.

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