Unveiling nonlinear absorption properties of 2,4-dihydroxybenzoic acid and nicotine amide metal complexes for optical limiting applications.

This study aims to compare the absorption and photoluminescence properties of 2,4 - dihydroxybenzoic acid and nicotinamide (HbN) metal (Cu, Zn, Co, Ni) complexes prepared in chloroform (CHCl3) and poly(methyl methacrylate) (PMMA) media and to reveal their potential for optical confinement applications. Narrower band gap energies of around 5.2 eV were obtained for complexes in PMMA matrices compared to pure PMMA (5.3 eV) due to defect states. Further, hypsochromic shifts were observed in the absorption spectra of the complexes in PMMA compared to CHCl3. The complexes indicated two photoluminescence (PL) peaks correspond to 430 and 750 nm wavelengths in both matrices. Slight hypsochromic shifts in PL spectra were observed for ZnHbN and NiHbN complexes in PMMA. In addition, the higher PL intensities were observed in PMMA matrices compared to CHCl3. Nonlinear absorption (NA) properties of the complexes in PMMA were examined by open aperture (OA) Z-scan measurements at 532 nm wavelengths with 4 ns (ns) pulse duration. CuHbN complex exhibited broader NA curve and higher NA coefficient (βeff = 1.60 × 10-5 m/W) at 17.7 MW/cm2 peak intensity than the other complexes. Additionally, optical limiting performance of the complexes are promising. The limiting thresholds are found to be 0.07, 1.27, 2.14, and 0.53 mJ/cm2 for CuHbN, ZnHbN, CoHbN, and NiHbN at 17.7 MW/cm2 intensity. Metal-organic complexes containing Cu, Zn, Co, and Ni in PMMA have significant potential for optical limiting applications.