Synthesis, growth, and characterization of natural dye-doped hexamethylenetetramine p-nitrophenol monohydrate single crystals for nonlinear optical applications

Integrating natural dyes into crystal structures represents an innovative frontier in materials science. This research examines the transformative effects of incorporating natural dye extracted from Cynodon dactylon (CD) into Hexamethylenetetramine p-nitrophenol monohydrate (HMP) single crystals. Single crystal X-ray diffraction analysis confirmed that both crystals crystallize in a triclinic system with a P1 space group. Hirshfeld surface analysis revealed stronger intermolecular interactions in the CD-HMP crystals. UV–Visible studies indicated a cut-off wavelength of 389 nm and transmittance of ~ 76% for CD-HMP crystals, compared to ~ 72% transmittance with a cut-off wavelength of 398 nm for undoped HMP. Photoluminescence studies revealed an emission peak at 577 nm for CD-HMP. FTIR spectroscopy and CHN analysis confirmed the presence of functional groups and the dye-crystal interaction in the crystal lattice. Dielectric studies assessed the electrical properties and thermal analysis revealed a decomposition temperature of 134 °C for CD-HMP, compared to 119 °C for HMP. Mechanical studies indicated that both are categorized as soft materials, with the work hardening coefficients of 1.74 and 1.71 for HMP and CD-HMP, respectively. The second harmonic generation (SHG) efficiency for CD-HMP was 1.15 times higher than that of undoped HMP, with a laser damage threshold of 2.29 GW/cm² for CD-HMP. Z-scan measurements demonstrated a third-order nonlinear absorption coefficient (β) of \(0.57\times {10}^{-10} m/W\) for CD-HMP crystals, along with effective optical limiting at \(3.78\times {10}^{12} W/{m}^{2}\). This synergistic enhancement of optical, thermal, mechanical, and nonlinear characteristics positions CD dye-doped HMP crystals as promising candidates for advanced nonlinear optical devices, with potential applications in optical communication and laser technology.