We have investigated the manifestations due to Manganese (Mn)-doping in ZnO sub-wavelength rods (or nanorods) on its nonlinear optical properties, namely two-photon absorption (TPA) and nonlinear refraction using single-beam Zscan technique. Mn-doped ZnO nanorods (NRs) were prepared by low temperature aqueous growth technique. The results show that Mn-doping concentration primarily determines whether ZnO NRs would exhibit saturable absorption (SA) or two-photon-absorption (TPA) characteristics in an openaperture experiment. At high Mn-doping concentrations, ZnO NRs exhibit SA behaviour which could be attributed to high occupation probability of defects states as well as saturation of linear absorption of subwavelength rod aggregates at high optical fluence. In contrast to high Mn-doping concentration in ZnO NRs, we observed TPA feature in 0.5% Mn-doped ZnO NRs. The employability of such structures in the area of optical limiting and switching is essentially derived from the possibility to tune the nonlinear optical absorption which could be realized by appropriate Mn-doping in ZnO NR architecture.
We report the synthesis of a unique zinc oxide nanorod structure in which an amorphous ZnO layer is sandwiched between two identical crystalline segments of ZnO. A simple hydrothermal reaction method was used for this purpose, which allowed us to tune the amorphous and crystalline sections of the nanorods via reaction temperature. A systematic study of the morphology and dimensions of the nanorods grown under various conditions was performed using a combination of scanning and transmission electron microscopy. Transmission electron microscopy (TEM) clearly showed an amorphous separation between the two crystalline segments. UV-vis absorption spectroscopy of the twin nanorods (TNRs) showed a redshift in the optical band gap as a function of the growth duration, indicating slightly stressed growth of the crystalline segments. For a longer growth duration, as the amorphous gap starts to get bridged by crystalline growth, redshift in optical band gap becomes constant. This confirms a true mechanical gap between the two crystalline segments of the nanorods. Temperature dependent photoluminescence (PL) spectra of the TNRs showed a variation in free exciton (FX) emission energy, which fitted very well to a model incorporating lattice dilation in addition to the standard electron-phonon interactions. At low temperatures (below ∼180 K) we observed the appearance of visible emission peaks due to localization of defect levels. A loss in the near band edge emission intensity was observed at low temperatures, commensurate with the appearance of defect emission in the visible range.
We report, temperature-dependent photoluminescence (PL) in temperature range between 77K to 300K, and room temperature nonlinear optical (NLO) properties of solution processed lead-free Cs2NaBiI6 (CNBI) and Cs2KBiI6 (CKBI) perovskite films....
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