Defect-induced tuning from reverse saturable absorption to saturable absorption in pristine and rare-earth-substituted MnCO3 microspheres

Cationic substitution in metal oxides induces defects that modify the ground state absorption and its nonlinear optical properties. Herein, the surface states, lattice disorders, and nonlinear properties of these microstructures are studied. The third-order optical nonlinearities of hydrothermally synthesized pristine MnCO3 and Ce3+ and Y3+ substituted MnCO3 microstructures are determined using single beam Z-scan transmittance analysis. As a result of controlling cationic defects in these microstructures, these materials exhibit tunable non-linear optical properties from Reverse Saturable Absorption (RSA) to Saturable Absorption (SA). The presence of surface states due to cationic substitution induces a transition from RSA to SA. The third-order optical nonlinearities exhibited by these microstructures when excited at a 633 nm continuous wave show enhanced efficiency which can be a potential candidate in optical switching applications.