Experimental and Computational Investigation of Fluorene Single Crystal for Optoelectronic and Scintillator Applications

Abstract

Fluorene (C₁₃H₁₀) single crystals (4 ×3 × 0.5 mm³) were grown via slow evaporation at room temperature to evaluate their potential for organic scintillator applications. Powder X-ray diffraction (PXRD) confirmed an orthorhombic crystal system. Ultravioletvisible (UVVis) spectroscopy showed a 3.7 eV optical band gap, 330 nm cutoff, and 52–70% transmittance. Proton nuclear magnetic resonance (¹H NMR) validated aromatic and methylene environments. Thermal analysis (TGA/DTA) revealed stability up to 113 °C, with defined melting and decomposition points. Photoluminescence (PL) exhibited blue emission at 428 nm under 330 nm excitation. Fourier-transform infrared (FTIR) and Raman spectroscopy identified functional groups and vibrational modes. Fluorescence lifetimes measured by time-correlated single photon counting (TCSPC) were 1.1 ns (prompt) and 5.1 ns (delayed), supporting fast response behavior. Density functional theory (DFT) with the B3LYP/6−311G++ basis set and time-dependent DFT (TD-DFT) described the optimized structure, HOMOLUMO gap, electrostatic potential, and excited states. Hirshfeld surface analysis showed dominant H···H interactions (54.3%), indicating efficient packing and energy transfer. Overall, fluorene exhibits desirable optical, thermal, and electronic properties, making it a promising material for organic scintillation detectors.