Optimizing excited state adsorption and carrier dynamics of metal doped zinc oxide by p-d orbital modulation for efficient reverse saturation absorption

Doping metals can regulate the excited state adsorption and carrier transport efficiency of ZnO through p-d orbital coupling thereby improving its nonlinear performance. Herein, the thin film coatings consisting of ZnO, and M-ZnO (M=Al, Sn, Mg) were synthesized using the magnetron sputtering technique. ZnO exhibited the granular/stick structure, while the metal dopant atoms (M) were incorporated into the ZnO lattice, resulting in a homogeneous distribution. Photoluminescence spectroscopy reveals the quenched defect emission intensity, indicating a decrease in the rate of photo-induced electron-hole pair complexation. Mg exhibits an optimized effect to promote the saturation absorption of ZnO, resulting in the enhancement of the nonlinear absorption (NLA) coefficients for M-ZnO films. Al-ZnO and Sn-ZnO films exhibit reverse saturation absorption. Theoretical simulation shows that the additions of transition metal atoms favor the electron transfer through p-d orbital modulation of ZnO. The p-d hybridization causes the metal-d orbitals to cross the Fermi level and form an electron transport channel, thereby enhancing the excited state absorption, and effectively controlling the NLA process and mechanism. The excited state absorption of the M-ZnO films significantly rises. This research demonstrates that the optimization of excited state absorption through p-d orbital modulation is a highly effective strategy for the development of efficient and superior nonlinear optical absorbers.