Low power optical limiting and thermal lensing in Mn doped ZnO nanoparticles

• Chemically synthesized Mn: ZnO nanoparticles exhibit hexagonal wurtzite structure.
• Zn vacancy defects are identified from PL spectra at 410 and 465 nm.
• Z-scan measurements using a 532 nm CW laser reveals the self-defocusing nature.
• Mn concentration dependent enhancement of NLO parameters is observed.

In the present work, third order optical nonlinearity of chemically synthesized ZnO nanoparticles with different concentrations of Mn (0–20 at %) has been investigated. All the prepared samples exhibit good crystallinity with hexagonal wurtzite phase. A blue shift in the excitonic absorption peak of ZnO (365–350 nm) due to Mn addition is identified from the optical absorption study. Further, emissions at 410 and 465 nm authenticate the presence of zinc vacancy in undoped ZnO and its enhancement in Mn doped samples. Nonlinear optical study carried out by Z-scan method using a 532 nm continuous wave laser excitation reveals the self-defocusing effect with negative sign of the nonlinear refractive index n2. The complex third-order nonlinear susceptibility (χ(3)) is estimated in the range (0.39–1.02) × 10−5 esu. In addition, optical power limiting is also found in Mn: ZnO nanoparticles with low threshold of 20.7 mW. The origin behind the observed nonlinearity and the limiting behavior are discussed in detail.

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