The properties of Er³⁺-doped gallium lanthanum sulphide thin films prepared on a silicon substrate by femtosecond pulsed laser deposition were studied as a function of process temperature. The films were characterised using transition electron microscopy imaging, X-ray diffractometry, Raman spectroscopy, fluorescence spectroscopy, and UV–Vis–NIR spectroscopy. The results show that by increasing the substrate temperature, the deposited layer thickness increases and the crystallinity of the films changes. The room temperature photoluminescence and lifetimes of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ are reported in the paper.

Over the years, vanadium dioxide, (VO₂(M1)), has been extensively utilised to fabricate thermochromic thin films with the focus on using external stimuli, such as heat, to modulate the visible through near-infrared transmittance for energy efficiency of buildings and indoor comfort. It is thus valuable to extend the study of thermochromic materials into the mid-infrared (MIR) wavelengths for applications such as smart radiative devices. On top of this, there are numerous challenges with synthesising pure VO₂ (M1) thin films, as most fabrication techniques require the post-annealing of a deposited thin film to convert amorphous VO₂ into a crystalline phase. Here, we present a direct method to fabricate thicker VO₂(M1) thin films onto hot silica substrates (at substrate temperatures of 400 °C and 700 °C) from vanadium pentoxide (V₂O₅) precursor material. A high repetition rate (10 kHz) femtosecond laser is used to deposit the V₂O₅ leading to the formation of VO₂ (M1) without any post-annealing steps. Surface morphology, structural properties, and UV–visible optical properties, including optical band gap and complex refractive index, as a function of the substrate temperature, were studied and reported below. The transmission electron microscopic (TEM) and X-ray diffraction studies confirm that VO₂ (M1) thin films deposited at 700 °C are dominated by a highly texturized polycrystalline monoclinic crystalline structure. The thermochromic characteristics in the mid-infrared (MIR) at a wavelength range of 2.5–5.0 μm are presented using temperature-dependent transmittance measurements. The first-order phase transition from metal-to-semiconductor and the hysteresis bandwidth of the transition were confirmed to be 64.4 °C and 12.6 °C respectively, for a sample fabricated at 700 °C. Thermo-optical emissivity properties indicate that these VO₂ (M1) thin films fabricated with femtosecond laser deposition have strong potential for both radiative thermal management or control via active energy-saving windows for buildings, and satellites and spacecraft.

In this paper, we report anatase and rutile titanium oxide (TiO₂) nanoparticulate thin films fabricated on silica and Indium Tin Oxide (ITO) substrates using femtosecond pulsed laser deposition (fs-PLD). Depositions were carried-out at substrate temperatures of 25 °C, 400 °C and 600 °C from anatase and rutile phase target materials. Effect of substrate temperature on the surface morphology, microstructural, optical, and electrical properties of these films were systematically investigated by using various range of measurements such as scanning electron microscopy, (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Ultraviolet–visible-near infrared (UV–Vis–NIR) spectroscopy, and Hall Effect measurements. It is observed that the TiO₂ thin films surface are predominated with nanoparticulates of diameter less 35 nm, which constitute about ~ 70%; while the optical bandgaps and electrical resistivity decrease with increasing substrate temperature. A mixed-phase (anatase/rutile) TiO₂ thin film was produced at a substrate temperature of 400 °C when samples are fabricated with anatase and rutile target materials. The results of this study indicate that the structural and crystallinity, optical, and electrical properties can be controlled by varying fs-PLD process parameters to prepare TiO₂ thin films, which are suitable for applications in photovoltaics, solar cells, and photo-catalysis.

There are significant challenges accompanied by fabricating a pure crystalline VO₂ (M1) thin film with an abrupt metal to insulator phase change properties. Most fabrication methods yield an amorphous VO₂ thin film that requires a post-annealing process to be converted into crystalline VO₂ (M1). Hence, the thickness of VO₂ (M1) films produced is very limited. In this work, we report the growth of pure VO₂ (M1) crystalline thin films onto a sapphire substrate in an oxygen atmosphere by the femtosecond pulsed laser deposition technique and using vanadium pentoxide (V₂O₅) as an ablation target. The thin films were deposited at substrate temperatures of 25 °C, 400 °C, and 600 °C, which reveal the crystallized structures of VO₂ (M1) without post-annealing. The thin film deposited at a substrate temperature of 600 °C exhibits a sharp and an abrupt metal-to-insulator transition (MIT) at a temperature of 66.0 ± 2.5 °C with nearly four orders of magnitude of the resistivity change (3.5 decades) and a narrow MIT hysteresis width of 3.9 °C. Furthermore, the influence of the substrate temperature, nanoparticle or grain size, and film thickness on the MIT parameters such as sharpness of the transition temperature, hysteresis width, and amplitude are discussed for potential applications of tunable antennas, terahertz planar antennas, and RF-microwave switches.

Various methods have been used to fabricate vanadium dioxide (VO₂) thin films exhibiting polymorph phases and an identical chemical formula suited to different applications. Most fabrication techniques require post-annealing to convert the amorphous VO₂ thin film into the VO₂ (M1) phase. In this study, we provide a temperature-dependent XRD analysis that confirms the change in lattice parameters responsible for the metal-to-insulator transition as the structure undergoes a monoclinic to the tetragonal phase transition. In our study, we deposited VO₂ and W-doped VO₂ thin films onto silica substrates using a high repetition rate (10 kHz) fs-PLD deposition without post-annealing. The XRD patterns measured at room temperature revealed stabilization of the monoclinic M2 phase by W⁶⁺ doping VO₂. We developed an alternative approach to determine the phase transition temperatures using temperature-dependent X-ray diffraction measurements to evaluate the a and b lattice parameters for the monoclinic and rutile phases. The a and b lattice parameters versus temperature revealed phase transition temperature reduction from ∼66 to 38 °C when the W⁶⁺ concentration increases. This study provides a novel unorthodox technique to characterize and evaluate the structural phase transitions seen on VO₂ thin films.

Erbium-doped nanocrystal (NC)-dispersed polymer thin films are attractive core materials for use in optical waveguides as they can provide high optical gain and enable the formation of compact waveguide amplifiers. Nonetheless, there are significant challenges associated with obtaining good dispersibility of NCs into a polymer matrix and favorable optical properties. Therefore, in this paper, we report the fabrication of Er³⁺-doped ceria (EGC) NCs employing the Leeds alginate process (LAP) and their incorporation into a siloxane polymer matrix. The surface morphology and compositional, structural, and optical properties of the fabricated films are evaluated to assess the NC dispersion and their suitability for the waveguide amplifier. The photoluminescence (PL) and lifetime measurements of the NCs–polymer nanocomposite thin film samples show intense, broadband PL emission of the Er³⁺ ions at 1534 nm (⁴I_13/2 → ⁴I_15/3 transition) with a full width at half-maximum (fwhm) of ∼64 nm and lifetime in the range of 2.6–3.0 ms. The inhomogeneously broadened PL spectra and improvement in lifetime of NCs in the polymer are important results that we report. The EGC NCs–polymer nanocomposite thin films also exhibit excellent transparency in the NIR wavelength range and a refractive index in the range of 1.53–1.58 in the visible wavelength. The work presented here clearly demonstrates the potential of using high-quality Er-doped nanocomposite polymer thin films for interesting applications such as compact low-cost waveguide amplifiers and lasers.