Sequential two photon absorption induced optical limiting action of oxide upconverter based MoS2 heterostructures

Abstract

Lanthanide ions (Yb, Er) doped cerium oxide (CeO2) and yttrium oxide (Y2O3) upconverter nanoparticles were prepared by sol-gel synthesis technique. And the upconverter nanoparticles (CeO2: Yb, Er and Y2O3: Yb, Er) were made us heterostructure with MoS2 by hydrothermal synthesis. XRD confirms the formation of cubic phase of CeO2, cubic phase of Y2O3, hexagonal phase of MoS2 and their coexistence in heterostructures. Further, the observation of characteristic Raman peaks between 400 and 700 cm−1 (Raman modes of CeO2, Y2O3) and 300–400 cm−1 (Raman modes of MoS2) assured the formation of heterostructures. FESEM exposes that in heterostructures nanospheres (CeO2: Yb, Er) and nanospindle (Y2O3: Yb, Er) were dispersed on MoS2 nanoplatelets. Furthermore, when forming the heterostructure with MoS2, the diameter of the CeO2 nanosphere got increased (90 nm) whereas, the length of the Y2O3 nanospindle was decreased (166 nm). The maximum absorption band occurred at UV region due to the charge transition from O2− to Ce ion or Y ion for CeO2 (340 nm) and Y2O3 (274 nm) respectively. Both upconverters exhibits interesting luminescence behaviour with green emission (537 nm, 588 nm), blue emission (497 nm) and red emission (621 nm). Nonlinear absorption induced optical limiting action were examined by open aperture Z-scan technique using nanosecond pulse laser. All the prepared nanoparticles exhibit a reverse saturable absorption pattern ascribed due to sequential two photon absorption. Among, all the samples, MoS2–CeO2: Yb, Er and MoS2–Y2O3: Yb, Er heterostructure possess a high nonlinear absorption coefficient (16.76 × 10−10 m/W, 13.61 × 10−10 m/W) and low limiting threshold (0.33 × 1012 W/m2, 0.51 × 1012 W/m2) due to the strong inter-band collision between of MoS2 and upconverters. The absorption of high number of photons and low limiting threshold behaviour make MoS2–CeO2: Yb, Er and MoS2–Y2O3: Yb, Er heterostructures as potential candidate for the fabrication of optical limiter based laser safety devices.