In this work, we present preliminary results of the fabrication and characterization of 1D Fabry–Perot microcavity realized on Yb3+ activated SiO2-SnO2 glass-ceramic (SiO2-SnO2:Yb3+). A radiofrequency-sputtering/sol-gel hybrid deposition process was developed for the microcavity fabrication. The fabrication included (i) radiofrequency-sputtering (rf-sputtering) of SiO2/HfO2 Bragg reflectors and (ii) sol-gel deposition of the active SiO2-SnO2:Yb3+ defect layer. A good control and enhancement of the spontaneous emission for Yb3+ luminescence sensitized by SnO2 nanocrystals was achieved exploiting microcavity properties. Such results are valuable for development of low-threshold rare-earth-based coherent light sources, pumped by broadband UV diodes.
SnO2-based glass-ceramics activated by rare earth ions have been extensively investigated because of the need to develop reliable fabrication protocols and clarify some interesting optical, structural, and spectroscopic features of the system. There is one important weakness in glass photonics when the rare earth ions are employed as luminescent sources. This is the low absorption cross section of the electronic states of the rare earth ions. A sensitizer is therefore requested. In the last years, we demonstrated that SiO2-SnO2 glass ceramics, presenting a strong absorption cross section in the UV range due to the SnO2 nanocrystal, are effective rare earth ions sensitizers. Another interesting property of the SiO2-SnO2 system is its photorefractivity. The high photorefractivity of sol-gel-derived SnO2-SiO2 glass-ceramic waveguides has been demonstrated in several papers published by our consortium. It has been shown that the UV irradiation induces refractive index change allowing the direct writing of both channel waveguides and Bragg gratings.
The results presented in this communication not only demonstrate the viability and outstanding properties of the SiO2- SnO2 glass-ceramics for photonic applications but also put the basis for the fabrication of solid state and integrated lasers. The next steps of the research are the fabrication of the channels and mirrors exploiting the photorefractivity as well as to draw glass ceramic fiber, checking the lasing action and corresponding functional characteristics. Finally, it is worth noting that the dynamic of the energy transfer from the nanocrystals to the rare earth ions is still an exciting open question.
Looking at the literature of the last years is evident that glass-based rare-earth-activated optical structures represent the technological pillar of a huge of photonic applications covering Health and Biology, Structural Engineering, Environment Monitoring Systems and Quantum Technologies. Among different glass-based systems, a strategic place is assigned to transparent glass-ceramics, nanocomposite materials, which offer specific characteristics of capital importance in photonics. These two-phase materials are constituted by nanocrystals or nanoparticles dispersed in a glassy matrix. The respective composition and volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramics. The key to make the spectroscopic properties of the glass-ceramics very attractive for photonic applications is to activate the nanocrystals by luminescent species as rare earth ions. From a spectroscopic point of view the more appealing feature of glass-ceramic systems is that the presence of the crystalline environment for the rare earth ions allows high absorption and emission cross sections, reduction of the non-radiative relaxation thanks to the lower phonon cut-off energy and tailoring of the ion-ion interaction by the control of the rare earth ion partition. Although the systems have been investigated since several years, chemical and physical effects, mainly related to the synthesis and to the ions interactions, which are detrimental for the efficiency of active devices, are subject of several scientific and technological investigations. Here we focus on fabrication and assessment of glass-ceramic photonic systems based on rare earth activated SiO2-SnO2 glasses produced by sol-gel route.
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