Demonstration of Enhanced Saturable Absorption in Upconverter Integrated MoS₂ Heterostructure Thin Film Using Nanopulsed Green Laser

Abstract

Upconverter/MoS2 heterostructure thin films were fabricated by simple hydrothermal technique. X‐ray diffraction and Raman studies assures the formation of upconverter/ MoS2 heterostructure. FESEM and HRTEM revealed that the nanobelt structured MoS2 mingled with trapezoid structure fluoride upconverters and sphere shaped oxide upconverters in films. Bandgap of MoS2 heterostructure films increased to 3.21 eV (NaYF4: Yb, Er), 3.72 eV (YF3: Yb, Er), 3.54 eV (Y2O3: Yb, Er) and 3.43 eV (CeO2: Yb, Er) than 1.98 eV (MoS2). Also the films exhibit green (to ) and red (to ) emission in heterostructure films. The influence of upconverters on the nonlinear absorption of MoS2 was exploited by single beam Z‐scan technique using nano‐pulsed laser (532 nm, 9 ns, 10Hz, 1‐5 GW/m2). The saturable absorption of the MoS2 is enhanced through integration with upconverter nanoparticles. Estimated ground state absorption cross‐section is higher than the excited state cross‐section of the samples and it confirms the occurrence of saturable absorption. Carrier relaxation time calculations show the interband transition plays a significant role in saturable absorption of heterostructure thin films. Saturable absorption coefficient varies in the order of MoS2‐CeO2: Yb, Er (‐5.65 X 10‐10 m/ W) > MoS2‐YF3: Yb, Er (‐3.87 X 10‐10 m/ W) > MoS2‐NaYF4: Yb, Er (‐3.22 X 10‐10 m/ W) > MoS2‐Y2O3: Yb, Er (‐2.34 X 10‐10 m/ W) > MoS2 (1.42 X 10‐10 m/ W). CeO2: Yb, Er @ MoS2 exhibit stronger saturable absorption due to synergetic effects like higher linear absorption coefficient at 532 nm, stronger green emission and reduced size with nanosphere morphology. Our results that pave way for the design of optical switches, Q‐switches and mode lockers based on saturable absorbers using upconverter integrated MoS2 thin films.This article is protected by copyright. All rights reserved.

Third-order optical nonlinearities of Nb4C3 MXene and its application as an ultra-broadband mode-locker

“…It was previously reported that nanomaterials with higher linear absorption coefficients possess larger nonlinear optical absorption. 83,84 It should be noted that Nb 4 C 3 MXene showed higher linear absorbance at 1900 nm wavelengths than that at 1560 nm wavelengths according to our measured linear absorption curve (Fig. 2d) and calculated curve (Fig.…”