Thermally Induced Phase Transition and Defect‐Assisted Nonlinear Absorption and Optical Limiting in Nanorod Morphology V₂O₅ Thin Films

Abstract

Materials possessing nonlinear and saturable absorptions received significant interest due to their applicability in various novel technological applications such as optical limiting, Q-switching, upconversion lasing, and mode locking. [1][2][3][4] Nonlinear optical properties of materials like nonlinear and saturable absorptions are highly affected by localized defect states that alter the bandgap energy (E g ) in the structure. These states could be altered by changing the thickness of the material, doping the material, and heat treatment and can be filled by one-photon absorption (OPA), two-photon absorption (TPA), and free carrier absorption (FCA) mechanisms. [5][6][7][8][9][10] Among these mechanisms, TPA is the dominant mechanism when a laser energy between E g /2 and E g is used.Recent studies on transition metal oxides revealed their potential for novel photonic devices using their nonlinear optical properties. [11][12][13][14][15] Among the other transition metal oxides, V 2 O 5 is one the most stable and easily synthesized material. [16,17] Various morphologies of the V 2 O 5 thin films about transition from semiconductor-to-metallic phase (SMT) were reported at a transition temperature of 257 C. [18,19] V 2 O 5 thin films can be easily deposited onto different substrates using diverse techniques such as thermal evaporation, [20] pulsed laser deposition, [21][22][23] magnetron sputtering, [24,25] chemical vapor deposition, [26][27][28][29] sol-gel process, [30,31] ultrasonic spray deposition (USD), [32] and spray pyrolysis. [33][34][35] Among all of the deposition techniques, the USD method is highly promising as it allows effective material utilization, relatively low deposition cost, and deposition under atmospheric conditions. Typical applications of V 2 O 5 thin films include but are not limited to gas sensors, [36,37] catalysis, [38] electrochromics, [39,40] and optoelectronic applications. [41] Although there are numerous studies on the diverse properties of V 2 O 5 in the literature, [42][43][44][45][46][47] in contrast, only a few studies reported the nonlinear optical properties of V 2 O 5 . Nonlinear absorption characteristics of V 2 O 5 and Na-doped V 2 O 5 nanoparticles prepared by solution combustion were investigated by Molli et al. and Pradhan et al., respectively. [48,49] Mousavi et al. reported third-order nonlinear optical properties of V 2 O 5 nanoparticles doped with Co, [50] and Ravinger et al. reported thickness-dependent nonlinear absorption characteristics of the V 2 O 5 thin films produced by sol-gel. [51] In this work, the effects of annealing on nonlinear absorption, nonlinear refractive, and optical limiting behaviors of ultrasonic

Negative Photoconductivity of Fe3GeTe2 Crystal with Native Heterostructure for Ultraviolet to Terahertz Ultra‐Broadband Photodetection

“…According to the two‐temperature model, [ 33 ] e‐e thermalization is faster than e‐ph thermalization after light excitation. Phonons will indirectly obtain energy through e‐ph coupling, leading to a heated lattice [ 34 ] (Figure 3a). As a result, some materials show a transition in crystal morphology due to the increase in structural disorder, which will cause a reduction in E g and a difference in electrical conductivity.…”

Morphology, defects and polymer concentration related nonlinear absorption and optical limiting properties of electrospun polyamide 6 nanofibers

“…This may be related to the localized defect states distribution inside the band gap. Our previous studies showed that defects have a great effect on the nonlinear absorption in amorphous and polycrystalline semiconductor thin films 59–61 . Polymer nanofibers, with enhanced scattering and prolonged path length (which increases light‐matter interactions), lead to enhanced nonlinear absorption.…”

“…Our previous studies showed that defects have a great effect on the nonlinear absorption in amorphous and polycrystalline semiconductor thin films. [59][60][61] Polymer nanofibers, with enhanced scattering and prolonged path length (which increases light-matter interactions), lead to enhanced nonlinear absorption. It is clear that these properties will be different for different morphologies, which are strongly affected by the electrospinning process and material parameters such as solution concentration, polymer density, high voltage applied, solvent and molecular weight of the polymer.…”

Tunable nonlinear absorption and optical limiting behavior of NaBi(MoxW1−xO4)2 single crystals with ratio of Molybdenum/Tungsten

“…The values of E U are calculated as 0.37, 0.17 and 0.15 eV for crystals 1, 2 and 3, respectively. Decreasing E U value with increase of the Mo/W ratio is the evidence of the decreasing defects in the structure [30,31].…”