Multifunctional Urea L-Malic Acid Crystals: Structural, Optical, Thermal, and Dielectric Insights for Optoelectronic Uses

Synthesis of the Urea l-malic acid (ULM) crystal was accomplished through a gradual evaporation growth technique. The characterization encompassed a thorough examination of its structural, spectral, optical, thermal, and dielectric aspects. The single-crystal X-ray diffraction (SCXRD) study elucidated a monoclinic pattern characterized by a non-centrosymmetric P2₁ space group. Fourier transform infrared (FTIR) study validated the existence of functional groups essential for hydrogen bonding and crystal sustainability. Optical investigations demonstrated significant UV absorbance at 261 nm, accompanied by a broad optical bandgap (4.185 eV). The Urbach energy was approximated at 0.228 eV, suggesting a high degree of crystallinity. A notable photoluminescence (PL) emission was detected at 460 nm, exhibiting a high degree of color purity at 77.15%, thereby endorsing its potential utility in blue-light display systems. Measurements of second-harmonic generation (SHG) showed that it was 2.2 times more effective than regular KDP, thereby underscoring its potential for nonlinear optical applications. The thermal stability was verified at temperatures reaching 120 °C, accompanied by a calculated activation energy (9.50 kJ/mol). Dielectric investigations revealed behavior that is dependent on both frequency and temperature, with AC conductivity exhibiting an increase in response to rising temperature. Impedance analysis demonstrated a non-Debye relaxation mechanism and a single semicircular Nyquist graph. The findings validate the multifunctional capabilities of ULM crystals for prospective applications in optoelectronic, photonic, and electrochemical systems.