Design,Fabrication And Optical Properties Of Transparent Nanocrystals-in-glass Composites

Applications of trivalent rare-earth(RE³⁺)doped light sources in solid-state laser technology,optical communications,biolabeling and solar energy management have stimulated a growing demand for programmable emission with flexible tunability and high efficiency.Codoping is a convention strategy for manipulate the photoluminescence of active RE³⁺ions.However,energy transfer between sensitizers and activators usually induces nonradiative migration depletion that brings detrimental luminescent quenching in the codoping systems.To solve the problem,we construct a nanoscopic heterogeneous architecture to spatially confine the RE³⁺clusters in the transparent framework via a“nanocrystals-in-glass composite”（NGC）structure.In this paper,we started with a theoretical stimulation to develop a designing principle for transparent broadband fluorescent NGC materials.The selection of activators,nanocrystals and glass matrix plays a crucial role in the fundamental characteristic and optical properties of NGC materials.Furthermore,we demonstrate how the incorporated nanocrystals chemically bonding to the glass matrix and the distribution of RE³⁺ions in NGC materials to manipulate energy depletion.Our detailed research includes the following three parts:1.Design principles of NGC materials and preparation of nanocrystals.Nanocrystal is the core of NGC materials which not only plays an important role for optical properties,but also manipulate the RE³⁺-ions distribution via selective spatial confinement,which provides new opportunities to block the migration-mediated depletion for enhanced efficiency.For NGC materials,it is significant to maintain the original fluorescence of nanocrystals while reduce the light scattering between nanocrystals and glass for high efficiency and transparency.In this chapter,we developed a design principle for transparent fluorescent NGC materials based on classic Mie theory.The relationship of theoretical transmittance of NGC between the particle size,refractive index and dopant concentration has been discussed in detail.Based on the simulation results,the diameter of individual nanocrystals in transparent NGC materials should be controlled to a critical value in which the scatter quenching induced by inhomogeneous boundary is not high and simultaneously reduces the thermal corrosion in nanocrystals.We also synthesized a serial of rare-earth based nanocrystals based on the optimal diameter.Evaluating by the thermal stability,microstructure and phonon energy,we selected YOF and YPVO₄ as nanocrystals matrix,which provides significant experimental support for subsequent preparation of transparent NGC materials.2.Tunable broadband near-infrared emission in transparent RE³⁺doped NGC via low- temperature co-sintering process.RE³⁺ions exhibit sharp spectral bands by the quantized 4fⁿ transitions,which exclude the extension applications in emerging areas that usually required a broadband and tunable emission.Great efforts have been made to expand the emission range of RE³⁺-doped materials,such as codoping.However,nonradiative energy transfer in homogeneous matrix could induce severe emission quenching since sensitizers and activators formed in broadband emission also have a matched resonant frequency.Energy migration process essentially relies on the interionic distance between sensitizers and activators.Therefore,it is possible to minimize the luminescent quenching by separating the RE³⁺emitters in a discrete spatial confinement with a distance larger than the fluorescence resonance energy transfer value.As a proof-of concept experiment,we choose the low-loss near-infrared optical communication window as the target model to demonstrate this bottom-up concept for tunable broadband emission with high efficiency.In this chapter,a NGC architecture is employed to assemble ordered RE³⁺-doped emitters to extend the emission spectral range by extracting photons from Nd³⁺,Tm³⁺and Er³⁺with a sequential energy gradient.The obtained RE³⁺-doped NGC materials with high emission intensity（nearly one order of magnitude enhancement）and broadband near-infrared emission from 1300 to 1600 nm,which covers nearly the whole low-loss optical communication window.3.Tunable multicolor generation in transparent NGC via solution-combustion process.In most cases,generating multicolor fluorescence in a single material needs to integrate heterogeneous structures with individual RGB emission into a monolithic architecture.Here,we report a simple and versatile bottom-up strategy to generate simultaneous multicolor emission with continuous tunability in a single monolithic material based on the NGC architecture.In our approach,a self-sustained low temperature solution combustion process enables homogeneous solvent dispersion and eventually stable immobilization of multiple nanocrystals in transparent matrix.By simply tuning the ratios of trichromatic nanocrystals,a full-range of emission colors with continuous tunability and optimized white light generation are demonstrated.With transparency of up to 80%,we further demonstrate drawing of fiber from the melt of these combustion-processed NGC materials.The optical spectral of the as-drawn glass fiber can be precisely tuned and clustering is effectively suppressed.Moreover,the NGC materials exhibit remarkable anti-thermal quenching behavior at temperatures of up to200^oC.The bottom-up strategy for NGC provides a versatile platform for the fabrication of high-performance multifunctional fiber-based devices for advanced applications in lasers,illumination,displaying and biophotonics.