Growth and multifaceted characterisation of phosphonium-based NLO single crystal: An efficient material for device and optical limiting applications

Phosphonium-based nonlinear optical materials (NLO) are gaining attention due to their unique molecular structure, tunable electronic properties, and strong intermolecular interactions, making them promising candidates in photonics and optoelectronics. Recognising the vital importance of these materials, a potential NLO single crystal of Ethyltriphenylphosphonium iodide hydrate (ETPI) was grown using the low-temperature solution method, achieving dimensions of 45 × 10 × 3 mm 3 at ambient temperature for the first time. The XRD analysis indicates that the crystal belongs to the monoclinic system with a space group of P21/C . The vibrational assignments were confirmed through FT-IR analysis. Optical absorption analysis reveals a cutoff wavelength of 280 nm and an optical bandgap of 4.43 eV. Evaluating Urbach energy and optical constants indicates good optical quality with a low defect concentration. The photoluminescence (PL) spectrum distinctly shows that the material emits a striking violet light, characterised by its specific wavelength range. Surface morphology and elemental compositions were assessed by HR-SEM/EDAX analysis. The laser damage threshold (LDT) power density was 7.5 GW/cm2, indicating its potential for high-power laser applications. The material exhibits negative photoconductivity, as evidenced by the observed photoconductive response. The thermal stability of the material was established through DSC analysis, revealing a melting point of 170°C. The dielectric constant and loss exhibit an exponential decrease with increasing frequency and varying temperature. Theoretical assessments of electronic polarizability were conducted. Third-order NLO properties were determined using the Z-scan approach, including the absorption coefficient (β), saturation intensity (Is), and optical limiting threshold, which were found to be 0.84 × 10-10 m/W, 39 × 1011 W/m2, and 3.41 × 1012 W/m2, respectively. These outcomes highlight the crystal’s suitability for integration into various nonlinear optical and photonic systems.