Preparation And Luminescence Modulation Of Glass Ceramics Based On Rare Earth Ion Induced In Situ Crystallization

In recent years,rare earth ion doped upconversion luminescent materials have been widely used in solar cells,solid state lasers,3D displays,optical data storage due to their multiple luminescence wavelengths and long emission lifetimes.Among them,rare earth doped oxyfluoride glass ceramics,combining the advantages of amorphous glass and fluoride crystals,are considered to be one of the most promising upconversion luminescent materials.However,the photoluminescence quantum yield of upconversion luminescence for conventional glass ceramic are always low（<1.0%）due to the mismatch of ionic radii and valence states during ionic substitution process,which makes it difficult for rare earth ions to controllably enter the crystal structure.In order to address this problem,a new strategy called“rare earth ion-induced in-situ crystallization”is proposed in this work for the design and preparation of glass ceramics with high-efficiency luminescence.The strategy is applicable to the preparation of all rare-earth ion-doped glass ceramics.A large number of rare earth ions spontaneously enter the fluoride crystal during the crystallization process,solving the problem of insufficient incorporation of rare-earth ions into the crystal in conventional glass ceramics and greatly enhancing the luminescence and laser efficiencies of oxyfluoride glasses ceramics.The main research contents of this paper are listed as follows:（1）A novel glass ceramic embedded with KYb₃F₁₀ nanocrystals were prepared and the microstructures and luminescence properties were investigated in this work.The precipitation of KYb₃F₁₀ crystals makes a large number of Yb³⁺ions enter fluoride crystal environment and the ionic distance is drastically reduced,greatly facilitating the formation of Yb³⁺-Yb³⁺ion pairs and greatly increasing the upconversion luminescence efficiency of Yb³⁺ions.When Tm³⁺and Eu³⁺ions are co-doped into the glass ceramic with Yb³⁺,the rare earth ions all enter the fluoride crystal structures.The upconversion luminescence of Tm³⁺and Eu³⁺ions are both enhanced through the energy transfer process.The modulation of blue and NIR upconversion luminescence has been achieved in Yb³⁺/Tm³⁺co-doped glass ceramics to obtain pure NIR upconversion luminescence.Additionally,red,green and blue upconversion luminescence was obtained in Yb³⁺/Eu³⁺co-doped glass ceramics by adjusting the ionic distances.The KYb₃F₁₀glass ceramics possess high optical transmittance and high luminescence efficiency,providing an excellent gain material for optical devices such as upconversion lasers,solid state lighting and information storages.（2）A series of rare earth ion-doped glasses with micro-phase-separated structures were designed to prepare oxyfluoride glass ceramics via heat treatments.The structure of glass network,crystallization mechanism,microstructure and optical properties of glass ceramics were deeply studied to extract a rare earth ions induce in situ crystallization strategy.In this strategy,the network structure of the glass was adjusted to regulate the distribution of rare-earth ions,resulting in the controllable precipitation of rare-earth fluoride nanocrystals in the glass.The crystallization in the glass ceramic is entirely dominated by the doped rare-earth ions.Firstly,the rare earth ions were completely confined in the fluoride glass network benefiting from the phase-separated glass network structure.Then the ions in the glass rearrange around the rare earth ions under the heat treatments to precipitate rare earth fluoride nanocrystals.Rare earth ions are spontaneously incorporated into fluoride crystal environment,avoiding the ionic replacement process in conventional glass ceramics.In this way,a large number of rare earth ions enter the fluoride crystal featuring low phonon energy compact structures in the glass ceramics.Thus,the problems of inadequate incorporation of rare earth ions into the crystal in conventional glass ceramics were solved,resulting in a much higher upconversion luminescence quantum yield（2.77%）than the conventionalβ-Na YF₄ glass ceramic（0.78%）.More importantly,this crystallization strategy is applicable to design all rare-earth ions doped glass ceramic.Various rare-earth fluoride nanocrystals could be precipitated and the luminescence efficiencies were significantly enhanced in the rare-earth ions doped glass ceramics.Furthermore,a microsphere laser demonstration was performed by using rare earth doped glass and glass ceramic as the gain medium.Comparing to the glass microspheres,the output power and laser slope efficiency of the glass ceramic microsphere laser were both greatly enhanced.The glass ceramics we designed exhibit high optical transmission,good thermodynamic stability and high luminescence efficiency,having large potential for applications in high power lasers,multi-color displays and lighting,and 3D information storages.The strategy rare earth ion induced in-situ crystallization strategy proves a perfect solution to the problem of uncontrolled incorporation of rare earths into crystals in conventional luminescent materials and paves up a new path for the development of high-efficiency optical gain materials.