Doped Glasses And Glass-Ceramics For Photonic Applications

In recent decades,upconversion(UC)luminescence in oxy-fluoride glass-ceramics(GCs)doped with rare earth(RE)ions has been extensively investigated due to their potential applications in the fields of upconverting laser,solar cell,color display and optical fiber.After heat treatment,a part of RE ions migrates from oxide region to the precipitated fluoride nanocrystals(NCs),resulting in the increase of luminescence efficiency by reducing the rate of nonradiative transitions.The UC luminescence in these kinds of materials can be improved by maximize the energy transfer between RE ions or tailoring the local environment of RE ions with transition metal ions or metal nanoparticles,while,the UC quantum efficiency is relatively low(?<1%)and the improvement of UC luminescence of oxy-fluoride GCs is still challenge to meet the requirement of most optical applications.To this end,we aim to understand the improvement of UC luminescence in RE doped oxy-fluoride GCs through investigating the local environments around RE ions and the local structure of the glass and GCs which have a strong influence on the UC emissions.We anticipate further enhancement of the UC luminescence by better understanding the detailed structure of the glass and GCs.In chapter 3,large enhancement in UC luminescence was verified in a transparent aluminosilicate GCs containing CaF2 NCs co-doped with Er3+ and Yb3+ ions.Based on the joint spectroscopic and structural characterizations,we suggest that the precipitation of fluoride NCs is correlated with the pre-existence of the fluoride-rich domains in the as-melt glass,which is supported by scanning transmission electron microscopy and reproduced by molecular dynamics simulation.The precipitation of the fluoride NCs starts from a phase-separated as-melt glass consisting of fluorine-rich and oxygen-rich domains,while the spatial distribution of RE ions and the vibration energies of the bonds connecting RE ions remain almost unchanged after crystallization.In the GCs,both the fluoride domain and the oxygen containing polyhedrons surrounding RE ions experience significant ordering which may affect the UC emission for both glasses and GCs.We therefore attribute the enhanced UC emissions of the GCs to the long-range structural ordering and the change of site symmetry surrounding RE ions,rather than the preference of RE ions in migrating from oxide-rich phase to the fluoride NCs.In chapter 4;we show that the observed UC luminescence enhancement in the GCs containing CaF2:Yb3+,Er3+NCs is greater than those doped with LaF3:Yb3+,Er3+NCs.Our joint experimental and theoretical studies suggest the larger enhancement of UC emission in CaF2-GCs is associated with the difference in the microstructures,the crystal size,the local coordination environment around RE ions as well as the structural rigidity in the silicate region of the GCs.There is no connection between low phonon energy and the observed highly efficient UC luminescence.In addition,it was found that a more symmetric ligand field around RE ions in a smaller size crystal which distributed more homogeneously within the highest ordering silicate region favors stronger UC emission by facilitating the energy transfer process and minimizing the rate of non-radiative relaxation process.In chapter 5,in case of oxide GCs,where the difference of phonon energy compared with that of glass can be neglected,we report UC luminescence enhancement in LaBGeO5:Yb3+,Er3+ GCs,surface crystallized glass-ceramics(SCGCs)and ceramics compared with its corresponding as-melt glass.Based on structural investigations,we find that the nucleation and crystallization of trigonal stillwellite LaBGeO5:Yb3+,Er3+ NCs occur first at the glass surface before the following volume crystallization.The local site symmetry around RE ions which is evaluated using the Eulu ions as a probe together with Judd-Ofeit theory calculations exhibits a clear increase with the devitrification of the glass.Consequently,complete crystallization of the glass leads to largest enhancement in the UC emissions of the LaBGeO5:Yb3+,Er3+ ceramics.We ascribe the enhancement of UC luminescence in the LaBGeO5:Yb3+,Er3+ GCs,SCGCs and ceramics to the structural ordering and the improvement of site symmetry surrounding RE ions that minimizes the rate of non-radiative relaxation process.Generally,our results may enrich our understanding about UC process in both of oxy-fluoride and oxide GCs and provide a general picture for the photophysical processes that contribute to the increase of UC luminescence efficiency in similar GCs systems for photonic applications such as solar cells and upconverting lasers.Integration of plasmonic nanostructures into solid state devices is a crucial step to realize numerous applications such as nanophotonics,biomedicine and energy.In addition to colloidal assembly and nanofabrication process like electron beam lithography,it is also possible to directly precipitate plasmonic nanoparticles(NPs)from solid transparent media,but curren tly remains limited to a few noble metal based systems.In chapter 6,we show that plasmonic Cu2-xSe NPs with an ultra-small size(?2 nm)can be precipitated from a borosilicate glass matrix through a self-conrinement solid state reaction between Cu+ and Se2-.The near infrared(NIR)localized surface plasmon resonance(LSPR)energy of the resultant plasmonic glasses is tunable by proper control of the reactions.The strong NIR-LSPR broadband of the Cu2-xSe NPs endows the plasmonic glass with strong nonlinear optical(NLO)response,which is characterized by an excitation-power dependent nonlinear absorption behavior.The intriguing NLO properties of the plasmonic glass doped with Cu2-xSe NPs may enable immediate applications such as optical switches and optical limiters.Metal-organic framework(MOF)glasses are a newly discovered family of melt-quenched glasses.In chapter 7,we show the discovery of the luminescent behavior of a MOF glass,i.e.,the cobalt doped zeolitic imidazolate frameworks-62(ZIF-62)glass(Zn1-x Cox(Im)1.9(bIm)0.1,x=0,0.1 and 0.5),which was obtained by melt-quenching of the corresponding ZIF-62 crystal.The synthesized crystal was precipitated in the form of spherical nano/micro-crystalline structure,which collapses structurally to form laminated glass with ultrahigh glass forming ability and the same short range molecular structure of the parent crystalline MOF.We observed the super-broadband mid-infrared(Mid-IR)luminescence(in the wavelength range of 1.5?m-4.8 ?m)both in the crystalline and amorphous phases.The observed Mid-IR emission originates from d-d transition of Co2+ ions that is protected by the strong Co-N coordination.The discovery of the luminescent MOF glasses may pave the way towards new photonic applications of bulk MOF glasses,such as Mid-IR lasers.