Upconversion Luminescent Glass-ceramics Based On Ternary Fluorosilicate Glass System

The up-conversion materials can convert long-wavelength light into short-wavelength light through two-photon or multi-photon absorption,for example,converting infrared light into visible light.Therefore,the up-conversion materials attracted broad attention in lighting display devices,solid-state lasers,solar cells,biomedicine and other fields.Rare earth ions has abundant emission levels and stable emission peaks.The excited state levels have long-lived characteristic and are often used as up-conversion luminescent dopants because their 4f-4f transitions are not allowed.Glass-ceramics is a new type of composite material,which consists of glass phase wrapped in nanocrystals.Glass-ceramics not only have the characteristics of easy preparation,low cost,excellent physical and chemical stability and mechanical properties,but also have good photoelectric properties of nanocrystals.By combining oxide glass with fluoride crystal,it not only solves the problem of high phonon energy of oxide glass,but also solves the problem of poor mechanical properties and stability of fluoride crystal.The obtained fluorine oxide glass-ceramics are especially suitable as rare earth ion doped matrix.In this paper,the upconversion luminescence properties of two rare earth doped fluorosilicates glass-ceramics with simple composition are studied.The upconversion luminescence of the sample after crystallization is greatly enhanced and has different characteristics.The details are as follows:The KMn F₃ glass-ceramics which has simple composition were designed and prepared（Si O₂-Mn F₂-KF）.It was found that the phase structure of glass-ceramics samples was characterized.After heat treatment,KMn F₃nanocrystals were precipitated in the glass.The average size of the crystals was about 4 nm,Because of the small size of the precipitated crystals in the GC（short for glass-ceramics）samples,Performance tests showed that the transmittance of GC samples was only slightly lower than that of the PG（short for precursor glass）samples.Especially in the red band.Transmissivity（T）is over 80%.The red upconversion luminescence of the Er³⁺is enhanced due to the regulation of the Mn²⁺on the luminescence of rare earth ions,which weakens the green upconversion luminescence,and makes the red-green ratio of the upconversion luminescence of the Er³⁺,R/G≈50,which makes the luminescence of the sample pure red.Meanwhile,due to the precipitation of KMn F₃ crystals,the upconversion luminescence intensity of GC samples is 10 times higher than that of PG samples,and the measured upconversion luminescence quantum efficiency is 0.10%±0.02%.A simple ternary fluoride glass-ceramics（Si O₂-YF₃-KF）was designed.Glass-ceramics containing KY₃F₁₀nanocrystals were obtained by conventional high temperature melting and heat treatment to control crystallization.Since KY₃F₁₀ nanocrystals have isotropic properties and the refractive index is highly matched with the glass matrix,although the GC samples has a high degree of crystallinity（～35%）,its transmittance is still good in the visible wavelength range of 300～700 nm（>90%）.High resolution transmission electron microscopy confirmed that the doped Yb³⁺/Er³⁺will enter the crystal phase.Due to the change of micro phonon environment,the green upconversion luminescence in the Er³⁺samples after heat treatment was significantly enhanced compared with the original glass（an increase of about 60 times）.At the same time,the luminescence properties of glass-ceramics with different ratios and the effect of preparation temperature on the properties of the samples were compared.At 10 W/cm² power density excitation source,green upconversion luminescence in glass-ceramics has a quantum efficiency of up to 0.41±0.02%.Under the same incentive conditions,its upconversion efficiency is comparable to that of ZBLAN:Yb³⁺/Er³⁺glass andβ-Na YF₄:Yb³⁺/Er³⁺glass-ceramics,almost twice as much as containing KYF₄:Yb³⁺/Er³⁺glass-ceramics.The developed high brightness upconversion luminescent glass-ceramics are expected to be used as a gain material in the field of solid laser and lighting.