Nonlinear photoresponse of NaYF:Yb,Er@NaYF nanocrystals under green CW excitation: a comprehensive study.

One of the efficient and well-known upconverting nanomaterials is NaYF:Yb,Er@NaYF, which emits photoluminescence at 545 nm and 660 nm under an excitation of 980 nm. Here, the nonlinearity of β-NaYF:Yb,Er@NaYF at 532 nm is investigated using three nonlinear approaches. For the first time, the nonlinear optical conjugation of NaYF:Yb,Er@NaYF nanocrystals is observed using the degenerate four-wave mixing method. In the optical bistability study, the optical hysteresis of NaYF:Yb,Er@NaYF is measured using the Mach-Zehnder interferometer nonlinear ring cavity, and the results of bistability loops show different behaviors at different power regimes. Finally, the -scan technique is used for determining the nonlinear absorption and refraction coefficients, which are calculated in the order of 10 (cm W) and 10 (cm W), respectively. The results indicate that by increasing incident powers, optical behaviour changes in both optical bistability and -scan. Therefore, the results exhibit that the β-NaYF:Yb,Er@NaYF nanocrystals have nonlinear photoresponses at both 980 and 532 nm, which could be promising for photonic devices based on NIR light and visible light.