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The implantation of bismuth during pulsed laser deposition (PLD) has been directly observed and investigated. Bi was deposited on amorphous aluminum oxide (Al[SUB2]O[SUB3]) and the laser energy density on the Bi target was varied by one order of magnitude (0.4 to 5 J cm[SUP-2]). Cross-sectional transmission electron micrographs reveal that, for laser energy densities above 2 J cm[SUP-2], in addition to the formation of Bi nanocrystals, there is a dark and apparently continuous layer in the Al[SUB2]O[SUB3] underneath them. From previous velocity measurements, the kinetic energy of the Bi species in the plume generated at laser energy densities above 2 J cm[SUP-2] has been estimated to be around 200 eV, which gives a calculated implantation range of 1.8 nm in Al[SUB2]O[SUB3]. This is in good agreement with the position of the Bi-rich layer. [ABSTRACT FROM AUTHOR]

Materials, and particularly glasses, with a tailor-made spectral optical response that can be switched in a controlled way using external stimuli excitation are of interest for the development of active optical devices, such as active filters or all-optical switching components. Based on the dielectric functions of solid and liquid bismuth (Bi), it is expected that both solid and liquid Bi nanostructures will show optical resonances with relevant different features in the near ultraviolet to near infrared. In addition, Bi has a low melting point that enables the solid–liquid phase change under moderate heating. Profiting of these singular properties we present and review in this paper the main results that have been obtained in our laboratory concerning the thermo-optical response of bulk germanate glasses and amorphous Al 2 O 3 thin films with embedded Bi nanoparticles (NPs). In both materials the optical transmission as a function of the temperature shows broad hysteresis loops. The optical contrast and width of these cycles depend on the Bi content and NP size. From the successful modelling of the optical properties of the Bi NPs-doped glasses, it is proposed that the observed material thermo-optical response arises from the change in the dielectric function of the Bi NPs upon melting, which induces relevant changes in the resonant optical behaviour of the Bi NPs. These results suggest that glasses with embedded Bi NPs are promising for the design of spectral-selective thermo-optical devices. [ABSTRACT FROM AUTHOR]

The optical transmission at a fixed visible wavelength of Bi nanoparticles embedded in a dielectric is known to show a sharp hysteretic evolution as a function of the temperature due to the reversible melting-solidification of the nanoparticles. In this work, we explore the temperature-dependent optical response of Bi nanoparticles embedded in a doped germanate glass (GeO2-Al2O3-Na2O) in a broad range from the visible to the near infrared. The transmission contrast induced by melting of the nanoparticles is shown to be strongly wavelength-dependent and evolves from positive to negative as the wavelength increases. This behaviour is well modelled using effective medium calculations, assuming that the nanoparticles size, shape, and distribution are unmodified upon melting, while their dielectric function turns from that of solid Bi to that of liquid Bi thus modifying markedly their optical response. These results open a route to the spectral tailoring of the thermo-optical response of Bi nanoparticles-based materials, which can be profitable for the engineering of wavelength-selective thermo-optical modulators and filters with optimized amplitude of modulation and wavelength dependence. [ABSTRACT FROM AUTHOR]

This work shows the influence of conditioning the Bi target previous to the pulsed laser deposition of Bi nanocomposite films on their optical and thermo-optical properties. The nanostructured films prepared by alternate pulsed laser deposition at room temperature in vacuum consist of Bi nanostructures (NSs) with different characteristic sizes that are organized in layers and embedded in an amorphous AlO host. Preablation of the Bi target prior to deposition leads to higher Bi concentration and Bi NSs with larger average sizes. As a result a lower optical transmission and an enhanced thermo-optical contrast are observed. [ABSTRACT FROM AUTHOR]

The synthesis by pulsed laser deposition of a bismuth nano-plane embedded in an amorphous germanium matrix is reported. The structural changes were studied by Raman spectroscopy as a function of temperature. Upon heating, the Bi nano-plane melts and, as the sample is cooled, it re-crystallizes at a temperature well below the melting point. The results show a broad melting–solidification hysteresis cycle (170 K) that is compared to the ones obtained earlier on nanoparticles. Furthermore, a metal-induced crystallization effect was also observed in the germanium matrix. [ABSTRACT FROM AUTHOR]

Structural properties as a function of temperature of bismuth nanocrystals embedded in amorphous germanium thin films, synthesised by laser ablation are investigated by Raman spectroscopy and X-ray diffraction. In addition to temperature anharmonic effects, Raman spectroscopy results reveal a melting solidification hysteresis, which takes place below the melting point of bulk bismuth. Furthermore, preliminary X-ray diffraction results suggest that the nanocrystals change in structure upon heating until melting occurs. However, the nanocrystals recover their original structure once the sample is cooled at room temperature. [Copyright &y& Elsevier]

Abstract. Bi nanoclusters embedded in an amorphous Ge matrix have been produced by alternate pulsed laser deposition in a vacuum. The resulting thin films have been analyzed by high resolution electron microscopy, and the images show that the Ge matrix is amorphous and that Bi nanocrystals are formed. The size of the nanoclusters was easily changed within the range 2 nm to 25 nm by varying the number of pulses on the Bi target. Both the dependence of the nanocrystal size on the number of laser pulses on the Bi target and the results of tilting experiments in the electron microscope show that the nanocrystals have an oblate ellipsoidal shape with a much shorter axis in the direction of the film normal. This particular shape is related to their growth mechanism after nucleation at the substrate. [ABSTRACT FROM AUTHOR]

Abstract: This work reports optical transmission changes in layered Bi nanostructures (NSs) upon heating–cooling cycles up to temperatures above the melting temperature. The nanostructured films prepared by pulsed laser deposition consist of Bi NSs with different characteristic sizes that are organised in layers and embedded in an amorphous Al2O3 host. The spectral dependence of the optical transmission as well as its changes upon heating are reported. The combination of Bi NSs layers with more than one characteristic size allows controlling the width of the melting–solidification transition. Eventually, it is shown how a multiple temperature thermo-optical film can be designed and prepared. [Copyright &y& Elsevier]

Melt-quenched borosilicate glasses, co-doped with Bi and V ions, exhibited broad visible spectrum emissions. Bi ions primarily existed as Bi3+, acting as network modifiers, lowering the glass transition temperature linearly with increasing Bi content. V5+ ions adopted tetrahedral coordination as [VO 4 ]3- units. Photoluminescence of Bi ions is shifted from blue to longer wavelengths with higher Bi content, associated with the stabilization of Bi2+ and the presence of Bi3+ in different local environments. Combined with V ions, the glasses emitted light covering the entire visible spectrum, offering the potential for white LED applications with correlated color temperatures ranging from 6135 to 4010 K. The highest QY was 11.9 and 8.0 % upon excitation at 325 and 340 nm. [ABSTRACT FROM AUTHOR]