Nonlinear optical (NLO) materials hold immense promise for revolutionizing optoelectronics and photonics. These materials exhibit a nonlinear response when interacting with light. This unique property translates into a vast array of applications, including advancements in signal communication, information processing via light, electro-optic switching elements, intricate photonic systems, military defense strategies, non-invasive medical diagnostics, and robust signal communication channels. Within the NLO realm, semi-organic materials stand out for their exceptional blend of properties. They combine the high optical nonlinearity characteristic of pure organic materials with the superior mechanical and thermal stabilities of inorganic materials. This winning combination translates into several advantages: high damage thresholds, broad transparency windows, minimal decomposition, excellent NLO coefficients, low angular dependence, and impressive mechanical characteristics. Growing these semi-organic crystals primarily involves the slow evaporation technique. This method entails mixing solvents and allowing them to evaporate gradually. This technique facilitates the growth of various crystals, including potassium boro-oxalate and bis(thiourea)cadmium chloride. Additionally, the gel diffusion method offers an alternative approach, where solvent diffusion occurs through a separating membrane. To assess the suitability of synthesized semi-organic crystals for NLO applications like laser frequency doubling, optoelectronic devices, optical bistability, and harmonic generation, researchers employ a battery of characterization techniques. These include X-ray diffraction analysis, Fourier-transform infrared (FTIR) spectroscopy, optical absorption studies, dielectric studies, dedicated NLO studies, and, importantly, optical transmission studies. The latter plays a pivotal role in gauging the crystal’s potential for various NLO applications.