Design,Synthesis And Property Tuning Of Doped Olivine-Germanate Luminescent Materials

Inorganic luminescent materials doped with transition and rare earth ions hold significant research value and extensive applications in various fields such as lighting and displays.In recent years,the exploration of new materials has extended to the near-infrared(NIR)and near-ultraviolet(NUV)invisible light ranges due to people’s pursuit of a healthier lifestyle.The former primarily focuses on the preparation of broadband NIR-emitting materials,which are used in applications such as non-destructive analysis and night vision illumination.The latter targets the development of NUV persistent luminescent materials for applications in encryption,anti-counterfeiting,and biomedical areas.Additionally,highly sensitive Boltzmann optical thermometers which utilize coupled energy levels of rare earth ions has also become a research hit in recent years.The development of new materials based on crystal structure models is an important guideline for the research of luminescent materials.Olivine as a common mineral type,it’s surprising that very limited-investigations have been reported on its optical properties.This thesis systematically investigates the relationship between structure and properties of olivine-type luminescent materials.It achieves all-round design of different types of luminescence based on olivine-type materials,thereby enriching their applications in the aforementioned fields.The details are as follows:(1)A series of broadband NIR-emitting materials(Mg1-xLix)(Mg1-xScx)GeO4:1%Cr3+were designed and prepared.By precise control of the crystallographic sites,the NIR luminescence can be largely tuned from 940 to 1110 nm,and the full width at half maximum(FWHM)can be modified from 236 to 300 nm.By adjusting the charge compensation and sintering temperature,the controllable valence states of Cr3+/Cr4+ ions in Mg2GeO4 can be achieved,leading to ultra-broadband NIR emission(FWHM up to 500 nm).Moreover,the relative intensity ratio of stark level transitions of Yb3+ exhibits potential applications in low-temperature(110-200 K)optical thermometry,with a relative sensitivity of approximately 1.69%K-1 at 110 K.(2)A series of excellent and stable upconversion luminescent materials LiAGeO4:Yb3+,Er3+(A=Sc,In,Lu,Y)were designed and synthesized.These samples exhibit unique upconversion luminescence properties,in which rare earth ions have abundant and resolvable Stark level splittings.By using the intensity ratio of the coupled 2H11/2/4S3/2→4I15/2 transitions and parts of the 4F9/2→4I15/2 Stark energy level transitions,sensitive optical thermometer(>1%K-1)within a wide temperature range spanning from 50 to 325 K can be realized.This offers new insights for the development of novel optical temperature sensing materials.(3)LiLuGeO4:Bi3+,Yb3+was designed as a NUV persistent luminescent material,with the peak emission wavelength around 356 nm and an afterglow duration longer than 15 hours.The investigation on afterglow mechanism indicates that the charging of the traps mainly comes from the charge transfer transition from Bi3+to the conduction band,and the redistribution of electrons from deep traps to shallow traps can be realized through the photostimulation process.