Investigation on the structural, spectral and third-order nonlinear optical characteristics of cytosinium dihydrogen monophosphate crystal

Good quality semiorganic single crystals of cytosinium dihydrogen monophosphate (CDHMP) have been grown by slow evaporation solution growth technique by using distilled water as the solvent. The grown crystal was subjected to single-crystal X-ray diffraction analysis to examine its structural characteristics. It possess that crystal belongs to centrosymmetric crystal system with space group P2₁/a. The powder X-ray diffraction analysis was carried out to identify the crystalline planes. It reveals good crystalline nature of CDHMP. The optical quality of the crystal was analysed by UV–Vis–NIR spectral technique. It shows CDHMP extends a wide transmittance window from 337 to 1100 nm. Functional groups present in CDHMP crystal were confirmed by FT-IR and FT-Raman spectral analysis. Nuclear magnetic resonance spectra were recorded to interpret the environment of proton and carbon in the molecular structure of CDHMP. The variations in the chemical shifts were observed due to the existence of N–H…O and O–H…O hydrogen bonds in the molecule. Photoluminescence measurement reveals that CDHMP crystal has high emission at 367 and 377 nm and it shows the ultraviolet fluorescence emission of the crystal. The third-order nonlinear optical properties such as refractive index (n₂), absorption coefficient (β) and susceptibility (χ³) were studied using the Z-scan technique at 632.8 nm with a continuous wave solid state laser. The χ³ value of CDHMP was found to be 0.9787 × 10^–7 esu. This high χ³ value is due to the occurrence of hydrogen bonds in the molecular structure. Thermal behaviour of CDHMP has been investigated through thermogravimetric and differential thermal analysis (TG/DTA).