Optical microcavities are key elements in many photonic devices, and those based on distributed Bragg reflectors (DBRs) enhance dramatically the end reflectivity, allowing for higher quality factors and finesse values. Besides, they allow for wide wavelength tunability, needed for nano-and microscale light sources to be used as photonic building blocks in the micro-and nanoscale. Understanding the complete behavior of light within the cavity is essential to obtaining an optimized design of properties and optical tunability. In this work, focused ion-beam fabrication of high refractive-index contrast DBR-based optical cavities within Ga 2 O 3 ∶Cr microwires grown and doped by the vapor-solid mechanism is reported. Room-temperature microphotoluminescence spectra show strong modulations from about 650 nm up to beyond 800 nm due to the microcavity resonance modes. Selectivity of the peak wavelength is achieved for two different cavities, demonstrating the tunability of this kind of optical system. Analysis of the confined modes is carried out by an analytical approximation and by finite-difference-time-domain simulations. A good agreement is obtained between the reflectivity values of the DBRs calculated from the experimental resonance spectra, and those obtained by finite-difference-time-domain simulations. Experimental reflectivities up to 70% are observed in the studied wavelength range and cavities, and simulations demonstrate that reflectivities up to about 90% could be reached. Therefore, Ga 2 O 3 ∶Cr high-reflectivity optical microcavities are shown as good candidates for single-material-based, widely tunable light emitters for micro-and nanodevices.

Tailoring the shape of complex nanostructures requires control of the growth process. In this work, we report on the selective growth of nanostructured tin oxide on gallium oxide nanowires leading to the formation of SnO 2 /Ga 2 O 3 complex nanostructures. nanowires grow preferentially. High-resolution transmission electron microscopy analysis reveals epitaxial relationship lattice matching between the Ga 2 O 3 axis and SnO 2 particles, forming skewer-like structures. The addition of chromium oxide to the source materials modifies the growth direction of the trunk Ga 2 O 3 nanowires, growing along the [001], with crossing SnO 2 wires. The SnO 2 /Ga 2 O 3 junctions does not meet the lattice matching condition, forming a grain boundary. The electronic and optical properties have been studied by XPS and CL with high spatial resolution, enabling us to get both local chemical and electronic information on the surface in both type of structures. The results will allow tuning optical and electronic properties of oxide complex nanostructures locally as a function of the orientation. In particular, we report a dependence of the visible CL emission of SnO 2 on its particular shape. Orange emission dominates in SnO 2 /Ga 2 O 3 crossing wires while green-blue emission is observed in SnO 2 particles attached to Ga 2 O 3 trunks. The results show that the Ga 2 O 3 −SnO 2 system appears to be a benchmark for shape engineering to get architectures involving nanowires via the control of the growth direction of the nanowires. KEYWORDS: Complex oxide nanowires, selective growth, crossed nanowires, transmission electron microsopy, cathodoluminescence A dvances in smart nanostructured materials require a deep understanding of the growth mechanisms to develop novel designs and architectures. Engineering new architectures will enable the combination of zero-, one-and two-dimensional systems enhancing the functionalities in comparison with their single counterparts (quantum dots, nanowires, or nanosheets). 1 Some physical properties, such as optical and transport properties, could be strongly dependent on the morphology of nanomaterials, hence nanomaterials with mixed dimensionality could offer extra applications. For example, light emission in nanowires may be affected if nanowires are assembled with quantum dots in the same nanostructure. 2 Beside dimensionality, we can even broaden out the tailoring capabilities of nanostructured materials by mixing several chemical elements or compounds. For instance, 1D-TiO 2 /2D-ZnIn 2 S 4 nanostructures with improved photocatalytic properties have been very recently reported. 3 Semiconducting oxides are an attractive family of smart materials with wide range of morphologies within the quasi-one dimension (nanowires, nanobelts, or nanorods). 4 Besides, these oxides offer a high versatility in the following applications: optical and mechanical resonators, lasing, sensors, photocatalysis, solar cells, and biomedical and healthcare usages to name a few. 5−8 A great deal of research has been...

Remote temperature sensing at the micro‐ and nanoscale is key in fields such as photonics, electronics, energy, or biomedicine, with optical properties being one of the most used transducing mechanisms for such sensors. Ga2O3 presents very high chemical and thermal stability, as well as high radiation resistance, becoming of great interest to be used under extreme conditions, for example, electrical and/or optical high‐power devices and harsh environments. In this work, a luminescent and interferometric thermometer is proposed based on Fabry–Perot (FP) optical microcavities built on Cr‐doped Ga2O3 nanowires. It combines the optical features of the Cr3+‐related luminescence, greatly sensitive to temperature, and spatial confinement of light, which results in strong FP resonances within the Cr3+ broad band. While the chromium‐related R lines energy shifts are adequate for low‐temperature sensing, FP resonances extend the sensing range to high temperatures with excellent sensitivity. This thermometry system achieves micron‐range spatial resolution, temperature precision of around 1 K, and a wide operational range, demonstrating to work at least in the 150–550 K temperature range. Besides, the temperature‐dependent anisotropic refractive index and thermo‐optic coefficient of this oxide have been further characterized by comparison to experimental, analytical, and finite‐difference time‐domain simulation results.

Gallium oxide microrods have been grown by an evaporation-deposition method by using a precursor containing lithium in order to check the influence of such dopant on the morphology and physical properties of the obtained β-Ga2O3 structures. SEM studies show that the morphology is modified with respect to undoped gallium oxide, promoting the growth of micropyramids transversal to the microwire axis. Raman analysis reveals good crystal quality and an additional Raman peak centred at around 270 cm -1 , characteristic of these samples and not present in undoped monoclinic gallium oxide. The presence of the Li + ions also influences the luminescence emission by inducing a red-shift of the characteristic UV-blue defect band of gallium oxide. In addition, an intense sharp peak centred around 717 nm observed both by cathodoluminescence (CL) and photoluminescence (PL) is also attributed to the presence of these ions. The Li related luminescence features have been also investigated by PL excitation (PLE) spectra and by the temperature dependence of the luminescence.

High quality Zn‐doped monoclinic gallium oxide micro‐ and nanostructures are obtained by a thermal treatment based on vapor–solid (VS) growth mechanism. Nanowires and ribbons are formed, the latter being the more abundant. The microstructural features are assessed by micro‐Raman and transmission electron microscopy revealing their crystal structure properties, such as the [‐110] growth direction for ribbons and being single crystals. In particular, a strong‐scattered light polarization dependence is reflected in the detected Raman modes. Luminescence of both Zn doped and undoped Ga2O3 samples is thoroughly studied by several techniques, exciting light with electrons or photons. Cathodoluminescence (CL) at a wide temperature range reveals that a band centered at around 2.7 eV, assigned to Zn doping in monoclinic Ga2O3, is thermally activated at temperatures above 200 K and dominates at room temperature. Besides, the characteristic bands at 3.4 and 3.0 eV of undoped Ga2O3 are obtained as well but with less relative intensity. Photoluminescence (PL) analysis at room temperature shows a similar set of bands, but slightly redshifted with respect to CL. Their relative intensities are strongly dependent on the excitation conditions and their time decays are studied by time‐resolved PL (TRPL).