The Preparation And Luminescence Properties Of Silver/rare-earth Ions Doped Luminescent Glass And Glass Ceramics

Molecular-like silver nanocluster?[Agm]ⁿ+?,with size between silver atom?Ag⁰?or silver ions?Ag⁺?and silver nanoparticles?Ag NPs?which is comparable to electron Fermi wavelength?sub-nanometer?,possesses discontinuous energy levels due to the quantum effect and exhibits advantages of high luminous efficiency,tunable band emission,excellent photochemical stability,etc.It shows broad application prospects in fields like spectral conversion,biosensing,energy and catalysis.However,how to stabilize the size of[Agm]n+ clusters and to disperse the clusters evenly remains a major challenge for researchers.In this thesis,inorganic glass network structure was used to stabilize silver clusters:[Agm]n+ with greenish white emission was formed by controlling the solubility of Ag+in glass matrix while[Ag²]²⁺ with red-orange emission was stabilized by negatively charged tetrahedrons.Furthermore,energy transfer between silver clusters and rare earth ions(Ln³⁺)in glass is utilized to broaden the excitation band of rare earth ions.This Ag/Ln co-doped luminescent glass might find its application for solar spectral conversion.In the multiphase glass ceramics,silver was selectively enriched in the boron-rich glass while the rare-earth ions were selectively enriched in the fluoride nano-crystal.This enrichment could effectively suppress the energy transfer between silver and rare-earth ions and largely enhance the luminous efficiency.These co-doped glass ceramic might find its application in white LED lighting.The thesis here is mainly based on the research of Ag/Ln doped oxyfluoride boroaluminosilicate system.The base glasses were prepared via high temperature melt-quenching method while the corresponding multiphase glass ceramics?containing silica-rich and boron-rich glass phases and fluoride crystalline phase?by the subsequent heat-treatment.The crystallization behavior of the glass was studied by differential thermal analysis?DTA?and X-ray diffraction?XRD?.The microstructure of the glass ceramic was studied by transmission electron microscopy?TEM?,scanning transmission electron microscopy?STEM?,energy dispersive X-ray spectroscopy?EDX?and selected area electron diffraction?SAED?.The local coordination of the glass network structure was studied by nuclear magnetic resonance?NMR?and X-ray photoelectron spectroscopy?XPS?.The spectroscopic characteristics of the glass and glass-ceramic were studied by absorption spectroscopy?UV-Vis-NIR?,photo-luminescence?PL?and time-resolved spectroscopy?TRES?.In glass matrix,silver was shown to exist in the form of Ag+,[Agm]n+,[Ag²]²⁺ or Ag NPs,while each of them exhibits characteristic luminescent properties due to its unique energy level structure.The transformation between different forms could be conducted by glass chemical methods.Finally,this thesis summarized the glass chemical conditions that needed to achieve heavy doping and high efficiency luminescence,and established the relationships among the composition,the structure and the luminescence properties in Ag/Ln co-doped glass and glass ceramic.1.By tuning the composition of the base glass,the solubility of Ag+ was adjusted effectively,[Agm]n+ was obtained through aggregation of Ag⁺ and Ag⁰.The main control measures are:?1?introduce B₂O₃ with high Ag+ solubility to achieve Ag heavy doping;?2?conduct appropriate heat treatment to reduce Ag⁺ to Ag⁰;?3?introduce Ag+ higher than its solubility.2.To achieve local charge balance,[Ag₂]²⁺ was formed by forcing two Ag+ to close attach to each other.In the glass network,[BO₄]-,[AlO₄]-and[ZnO₄]^2-are non-equilibrium charged,near[ZnO₄]^2-or two neighbored[BO₄]/[AlO₄]-two Ag+,by forming[Ag2]2+,can act as charge compensator to achieve local charge balance.Glass with composition 56SiO₂-15Al₂O₃-14CaF₂-10ZnF₂-5B₂O₃-1AgNO₃ exhibits typical[Ag₂]²⁺ red-orange emission with QY as high as 81.2%.When introduced into glass system,other monovalent ions would compete with Ag+ for the charge-compensating position and inhibit the formation of[Ag₂]^2-.Herein,through fine adjustment of Ag+doping host glass composition,the emission color could be tuned in a wide range.3.To broaden the excitation of Ln³+ through energy transfer from silver clusters to Ln³+ in the glass.By silver/rare-earth co-doping,the luminescence intensity and spectral response of Ln³+ were improved effectively owing to energy transfer from Ag⁺,[Ag_m]ⁿ⁺ or[Ag₂]²⁺ to the rare-earth ions(Ln³⁺).This sort of materials could be used to realize solar spectrum conversion to improve the efficiency of silicon solar cell.4.To improve the luminous quantum efficiency of the glass ceramics by selectively enrichment of Ag and Ln into different phases.Based on this principle,Ag/Er,Ag/Ho,Ag/Nd co-doped glass ceramics can obtain about 2 times the luminous quantum efficiency of the precursor glass.