<p>The single crystal of CN₂H₅HgI₃ was grown at room temperature using a solution method. Utilizing first-principles density functional theory, the electronic structure and optical properties of CN₂H₅HgI₃ crystals were investigated through the generalized gradient approximation (GGA + U) approach. The single crystal analysis results indicate that CN₂H₅HgI₃ exhibits a triclinic structure with a space group of P-1. CN₂H₅HgI₃ is identified as a direct band-gap semiconductor with a band gap of 3.07 eV, making it suitable for applications in ultraviolet detection materials. The energy levels of the electrons at the top of the valence band and the bottom of the conduction band are primarily derived from Hg, I, C, N, and H. CN₂H₅HgI₃ is formed through electrostatic interactions between CN₂H₅⁺ and [HgI₃]⁻. By combining the density of states, dielectric constant, and absorption coefficient, the characteristics of electron transitions were discussed. The results obtained from the UV–Vis-NIR spectra indicate that the band gap of the CN₂H₅HgI₃ crystal is 2.59 eV, which is lower than the calculated band gap of 3.07 eV. Theoretical calculation was verified via fluorescence spectroscopy, which showed that CN₂H₅HgI₃ exhibits a pronounced exciton luminescence effect at room temperature, with a first exciton binding energy of 480 meV. This is significantly higher than the exciton binding energies of similar compounds&#xa0;CH₃NH₃HgI_3&#xa0;(166 meV)&#xa0;and (CH₃NH₃)₂HgI₄&#xa0;(256&#xa0;meV). Our analysis of the electronic structure and energy band of the crystal suggests that CN₂H₅HgI₃ has potential applications as an ultraviolet detector material and exciton luminescent material.</p>