Up-conversion Luminescence Of Yb³⁺/Mn²⁺ Co-doped Transparent Oxyfluoride Glass Ceramics

Up-conversion（UC）is an anti-stokes luminescence process that can emit short-wavelength photon by absorbing long-wavelength photon,which have found significant applications on solid-state lasers,biomarker,laser materials and so on.In recent years,optical functional materials based on UC have steadily become as the main research direction and hotspot in the field of luminescence owing to the rapid development of novel laser and nanotechnology.In most cases,UC materials were focused on rare earth（RE）ions doped systems.Unfortunately,the fixed emission peaks and narrow emission bandwidths inevitably restricts the further development of RE ions activated UC materials.Rare earth/transition metal ion co-doped systems,such as Yb³⁺/Mn²⁺co-doped in the single host,can realize tunable broadband UC emission under the excitation of a 980 nm laser diode（LD）,which is expected to make up for the weaknesses of UC materials based on RE ions.However,for a long time,the Mn²⁺-UC emission occurred only in microtherms and was quenched at room temperature.So far,such room-temperature UC luminescence is limited to a few cases in Yb³⁺/Mn²⁺co-doped powder materials,which is urgent to expand its host species.Comparing to powder materials,transparent glass ceramics benefit from the excellent luminescent properties of nanocrystals in combination with the high physic-chemical stability of glass matrix,are considered as most promising host materials.Thus in this dissertation,we focus on researching of Yb³⁺/Mn²⁺co-doped transparent glass ceramics with oxyfluoride nanocrystals.The tunable broadband emission performance was observed by controlling Mn²⁺contents and heated temperature.The crystallization behavior,microstructure,and（high temperature）UC spectral characteristics of the prepared glass ceramic samples were systematically analyzed using X-ray powder diffraction,high-resolution electron microscopy,absorption spectroscopy,and fluorescence spectroscopy.The paper is divided into four chapters.The 1st chapter depicts the mechanism of UC luminescence,the recent progress and current state of RE or transition metal ion doped luminescent materials and Yb³⁺/Mn²⁺co-doped luminescent materials.This chapter also emphatically summarizes the characteristics and application prospect of glass ceramic,and then points out the research contents of this work.The 2nd and 3rd chapters introduce the related investigation on broadband luminescence and mechanism of Yb³⁺/Mn²⁺doped transparent glass ceramics.The conclusion part is described in the 4th chapter and the principal achievements are summarized as follows:1)Yb³⁺/Mn²⁺co-doped transparent glass ceramic containing β-YF₃andγ-Ga₂O₃nanocrystals have been successfully prepared using the melt-quenching method.XRD and TEM techniques indicate two nanophases,i.e. β-YF₃ andγ-Ga₂O₃,precipitate in the glass matrix.Under 980 nm pumping,tunable dual-emission visible bands peaking around 520 nm and 605 nm,associated with|²F_7/2,⁴T₁（⁴G）>→|²F_7/2,⁶A₁（⁶S）>transitions of Yb³⁺-Mn²⁺dimers in the tetrahedral and octahedral coordination sites,respectively,were obtained from the resultant glass ceramic.Based on the in-depth analysis of spectral characteristics and fluorescence lifetimes measurements,a ground state/excited state absorption UC mechanism based on the Yb³⁺-Mn²⁺dimer is proposed.2)Yb³⁺/Mn²⁺/Tm³⁺tri-doped dual-phase transparent glass ceramic containingβ-YF₃andγ-Ga₂O₃nanocrystals have been synthesized by a melt-quenching method.Upon excitation of a 980nm LD,the Yb³⁺/Mn²⁺co-doped glass ceramic shows tunable luminescence between the light yellow and the orange region.After blue emitter Tm³⁺ion was introduced into the co-doped system,tunable emitting color between the blue and the orange region has been obtained by varying the content of Mn²⁺,and a perfect white-light emission with CIE coordinates（x=0.335,y=0.314）was realized,which is ascribed to the energy transfer from Tm³⁺→Yb³⁺-Mn²⁺.Detailed UC spectroscopy analysis and mechanism explanation were given for the above processes.In addition,the temperature dependent UC emission spectra presented a good thermal recoverability for the resultant Yb³⁺/Mn²⁺/Tm³⁺tri-doped glass ceramics.In this work,the crystallization behavior,luminescence characteristics and energy transfer process of Yb³⁺/Mn²⁺co-doped oxyfluoride transparent glass ceramics were studied in detail.The research focuses on studying the effect of heat treatment temperature and type of the precipitated nanocrystals in glass ceramics as well as the concentration of dopants on the UC luminescence properties.The tunable broadband UC emission and white-light output were obtained by designing the Mn²⁺doping content and precipitation of crystals of transparent glass ceramics.The exchange-coupled Yb³⁺-Mn²⁺dimer and involved UC mechanism were thoroughly investigated.This research contributes to a better understanding of the UC process of Yb³⁺/Mn²⁺in transparent hosts and provides a good guiding significance for expanding the application of transparent glass ceramics in the field of UC luminescence.