Exploring optical, electronic and NLO properties: Growth and characterization of rubidium hydrogen (+)- tartrate crystals

Rubidium, a highly reactive alkali metal, is used in several research areas, such as electronics for its light-emitting properties, and in making glass, ceramics, and in biomedical studies. Single crystals of Rubidium Hydrogen (+)-Tartrate (RHT) suitable for the X-ray analysis were obtained from water solution. The crystal structure of the RHT crystal was determined using single crystal XRD, revealing an orthorhombic system with a non-centrosymmetric space group, P2₁2₁2₁. The lattice parameters were a = 7.9233 Å, b = 10.9883 Å, and c = 7.6527 Å, with a unit cell volume of 666.272 Å³. The structural vibrations of the RHT compound were analysed using FT-IR and FT-Raman spectroscopy, while NMR provided further insights into its molecular structure. Theoretical investigations at the DFT/RB3LYP/LANL2DZ level were conducted to explore the molecular structure, vibrational spectra, and bonding interactions within the RHT compound's molecular system. Natural Bond Orbital (NBO) analysis of the RHT compound revealed significant charge transfer interactions and stabilization energies, particularly highlighting strong electron donor-acceptor correlations that contribute to the molecule's overall stability. The UV–Vis and HOMO-LUMO calculations were performed in the gas phase. Optical conductivity studies have been performed. The broad spectral curve in the photoluminescence spectrum reflects the optical effects and showed a significant intense peak at 281.22 nm and a moderately intense peak at 395.9 nm. First order hyperpolarizability studies reveals that nonlinear optical efficiency is 1.06 times better than urea and 58.19 times than KDP. Furthermore, Third Harmonic Generation (THG) studies using the Z-scan technique were also conducted to investigate the nonlinear properties.