Third-order nonlinear optical properties of the small-molecular organic semiconductor tris (8-Hydroxyquinoline) aluminum by CW Z-scan technique

The linear optical and electroluminescence properties of small molecular organic material tris-(8-hydroxyquinoline) aluminum (Alq3) are known and extensively investigated by many studies. However, the studies on the nonlinear optical (NLO) properties of this material are still scarce. Herein, the third-order NLO (TONLO) properties of Alq3 chloroform solutions with different concentrations have been examined using the Z-scan technique. At different laser powers and different laser wavelengths, the Z-scan signals were recorded using a continuous-wave (CW) laser beam. The open-aperture (OA) and closed- aperture (CA) Z-scan signals revealed strong TONLO properties. Both nonlinear refractive index (n2) and nonlinear absorption coefficient (β) showed negative values, and their smallest values were in the fold of 10−8 cm2/W and 10−2 cm/W, respectively. The negative values of n2 and β suggest thermal nonlinearity and saturable absorption (SA), respectively. The TONLO susceptibility (χ(3)) was calculated and found to be in the order of 10−6 esu. Besides, they increased with increasing the concentrations of Alq3 and laser powers. Therefore, the results indicate that Alq3 could be one of the potential materials as a saturable absorber for starting a passive mode-locking operation.