Unveiling two-photon absorption dynamic in melt grown 2,4-dihydroxybenzophenone (DHBP) single crystal: Insights from bridgman method using double-zone glass furnace

Abstract

In this study, a single crystal of 2,4-dihydroxybenzophenone (DHBP) was grown using the vertical Bridgman method using a custom-designed double zone furnace. DSC revealed the melting and freezing points of DHBP as 149 ℃ and 61 ℃, respectively. A transparent Bridgman furnace with a steep temperature gradient was employed to accommodate the significant phase change temperature difference. The conventional V-shaped ampoule was modified with a shorter cone length and angle to optimize the growth process. X-ray diffraction (XRD) confirmed the monoclinic structure (P2_1/c) of the DHBP crystal retained post-melting and crystallization. High-resolution XRD revealed excellent crystalline perfection of the grown DHBP crystal with an FWHM of 154” for the (0 2 0) lattice plane. The FTIR and FT-Raman analyses confirmed the functional groups of the melt-grown DHBP single crystal aligned well with those of the solution-grown crystal. The grown DHBP shows 70 % transmittance (450–1000 nm), a 390 nm cut-off, an optical band gap of 3.13 eV and an Urbach energy of 0.11 eV. Photoconductivity analysis revealed that the as-grown crystal in the (0 2 0) plane acquired negative conductivity. Photoluminescence studies revealed fluorescence at 530 nm under 390 nm excitation. A Z-scan experiment was performed using both CW He-Ne laser (632 nm) and Nd:YAG pulsed laser (532 nm) to explore third-order NLO properties. The DHBP crystal demonstrates reverse saturable absorption, attributed to the phenomenon of two-photon absorption. According to pure electronic nonlinearity, the nonlinear absorption coefficient and optical limiting threshold were determined to be 5.4 × 10⁻¹¹ m/W and 3.24 × 10¹² W/m², respectively.