Optical Kerr nonlinearity and ultrafast photo-excited carrier dynamics in CePO4/g-C3N4 heterojunctions: mechanistic insight into a 3D/2D interface for optical limiting

Abstract

Stable and effective optical limiters have been of great significance in protecting human eyes and opto-electronic sensors ever since the invention of high-power lasers. The present work explores the ultrafast optical limiting property and optical Kerr nonlinearity of facile wet-chemical-exfoliated CePO₄/g-C₃N₄ type-II heterojunctions. Photophysical and third-order optoelectronic nonlinearities were investigated via single-beam femtosecond (∼50 fs, 800 nm) and nanosecond (∼9 ns, 532 nm) Z-scan techniques. Cerium orthophosphate heterojunctions with exfoliated graphitic carbon nitride reveal enhanced two-photon absorption in NIR (800 nm) and visible (532 nm) light pulses with magnitudes of ∼10⁻⁸ m W⁻¹ and ∼10⁻¹⁰ m W⁻¹, respectively. At the 3D/2D interface, positive nonlinear refractive index and third-order susceptibility were calculated to be ∼10⁻¹⁵ (cm² W⁻¹) and 10⁻¹⁴ e.s.u., respectively. Electronic band alignment, molecular orbital contributions, and Fermi level energy calculations using density functional theory, linear absorption and emission characteristics favor pronounced carrier dynamics in inorganic–organic hybrids. In addition, the Kane energy and exciton reduced mass as well as physical parameters determining the oscillator strength of the electronic transition and carrier mobility were calculated. Strong reverse saturable absorption projects CePO₄ and CePO₄/g-C₃N₄ as smart optical limiters for femtosecond and nanosecond laser pulses.