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Solvent-dependent fluorescence dynamics and ultrafast optical nonlinearity in Tectona grandis L.f. leaf extract
C Beryl1, M S Amogh1, Varsha Vijay2
1Ultrafast and Nonlinear Optics Lab, Light and Matter Physics Group, Raman Research Institute, Bangalore 560080, India; School of Pure and Applied Physics, Mahatma Gandhi University, Athirampuzha, Kerala 686560, India.
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The nonlinear optical properties of natural dye extracts derived from Tectona grandis L.f. (teak) leaves were systematically investigated in solvents of varying polarity using the Z-scan technique in the ultrafast domain. UV-visible absorption and FTIR spectroscopy confirm the presence of chlorophylls, carotenoids, anthocyanins, phenolics, flavonoids, tannins, and glycosides in Tectona grandis L.f. (teak) leaf extract, while time-correlated single-photon counting (TCSPC) measurements reveal pronounced solvent-dependent multicomponent excited-state decay dynamics. Femtosecond Z-scan experiments performed using a high-repetition-rate Ti:Sapphire laser (100 fs, 800 nm, 82 MHz) show strong nonlinear absorption accompanied by negative nonlinear refraction for all solvent extracts, indicating reverse saturable absorption (RSA) and self-defocusing behavior. At higher incident powers, the open-aperture Z-scan curves for the toluene and dichloromethane extracts exhibit characteristic W-shaped profiles, signifying saturation of excited-state absorption due to state-filling and population bottleneck effects. Analysis using an intensity-dependent absorption model yields effective nonlinear absorption coefficients (βeff) in the range of 10-6-10-5 m/W and nonlinear refractive index coefficients (n₂) of the order of 10-15 m2/W. The nonlinear response shows strong solvent dependence: carbon tetrachloride exhibits enhanced nonlinear absorption at low intensities due to aggregation-assisted ESA, whereas polar aprotic solvents such as DMSO and DMF display pronounced self-defocusing nonlinearity governed by cumulative thermally induced refractive index changes supported by long-lived excited-state populations. The combined Z-scan and TCSPC analysis establishes teak leaf extract as a solvent-tunable, bio-derived nonlinear optical material with potential applications in optical limiting, optical switching and in various photonics applications.
