| Developing a single material inheriting both the FIR ratio and lifetime-based temperature sensing performances is going to be of vital importance in optical temperature sensing.A multi-phase glass ceramic have the added advantage of Ln3+and TM ions co-doped into a single host material which realizes both the FIR for Ln3+and luminescence lifetime for TM ions together for effective temperature sensing.Although,multi-phase GC exhibits simultaneous realization of both FIR and luminescence decay lifetime providing effective temperature sensing,but at the same time,doping both Ln3+ and TM ions into same host material results into quenching of the luminescence due to adverse energy transfers between the different active centers.The characteristic host for co-doped Ln3+/TM ions is oxy-fluoride GC,where Ln3+ and TM ions could be partitioned into different host environments and it suppresses energy transfer between different active ions without compromising the individual ions original luminescence efficiencies.So it is highly enviable to develop a multi-phase GC optical temperature sensor that could provide accurate temperature sensing over a wide temperature range.In this thesis,two different glass formulations were used,respectively((44+x)SiO2-(26.95-x)Al2O3-10ZnF2-20CaF2-3ErF3-0.05CrF3,(42+x)Si02-(24.90-x)Al2O3-10ZnF2-20SrF2-2YbF3-1 ErF3-0.10CrF3.Different concentrations of Yb3+/Er3+/Cr3+-doped fluorosilicate glass were prepared by high-temperature melting method.Thermal analysis(DTA),X-ray powder diffraction(XRD)and transmission electron microscopy(TEM)were used to study the heat treatment of the glass structure and micro-morphology.Through the fluorescence emission spectrum and fluorescence lifetime test methods,the position of Yb3+/Er3+/Cr3+ in the glass matrix was studied.By fitting a series of fluorescence intensity ratio and fluorescence lifetimes to the corresponding temperatures,relevant parameters about the temperature sensing performance of the test sample are obtained.1.Oxyfluoride transparent glass-ceramics(GC)containing CaF2 and ZnAl2O4 nanocrystals have been fabricated with melt-quenching method.By carrying out the heat treatment of the precursor glass(PG),Er3+ and Cr3+ were selectively partitioned into CaF2 and ZnAl2O4 nanocrystals,respectively.The partitioning of the Er3+ and Cr3+ions into CaF2 and ZnAl2O4 nanocrystals,respectively,suppressed the energy transfer between different active ions without compromising the individual ions original luminescence efficiencies.The obtained multi-phase GC thus exhibited strong upconversion(UC)fluorescence of Er3+ as well as intense down-conversion(DC)fluorescence of Cr3+.Further,under 980 nm excitation,the green UC fluorescence of Er3+due to 2H11/2,4S3/2?4I15/2 transition and the red DC fluorescence lifetime of Cr3+due to E,4T2?4H2 transition were found to be highly dependent on the temperature and making them possibly suitable for Optical Thermometry.With least square fitting methods,the FIR of Er3+ from thermally coupled energy states(2H11/2 and 453/2)produced maximum temperature sensing sensitivity values of 0.33%K-1 at 437 K and 0.36%K"1 at 267 K,respectively.Similarly,fluorescence lifetime of Cr3+ attributed to the parity forbidden(2E?4A2)and spin allowed(4T2?4A2)produced the maximum temperature sensor sensitivity value equal to 0.67%K-1 at 535 K.2.An Oxy-fluoride precursor glass(PG)obtained via melt-quenching method was converted into a transparent multi-phase oxy-fluoride glass-ceramic(GC)having SrF2 and ZnAl2O4 nanocrystals to explore its potential application in optical thermometry.Heat treatment strategy was utilized to convert PG into GC that selectively partitioned Yb3+/Er3+ and Cr3+ into SrF2 and ZnAl2O4 nanocrystals,respectively.The partitioning of the Yb3+/Er3+ and Cr3+ into SrF2 and ZnAl2O4 nanocrystals,respectively,suppressed the energy transfer between different active ions without compromising the individual ions original luminescence efficiencies.The obtained multi-phase GC thus exhibited strong upconversion(UC)fluorescence of Er3+ as well as intense down-conversion(DC)fluorescence of Cr3+.Under 980 nm excitation,intense green(UC)luminescence attributed to Er3+:2H11/2,4S3/2?4115/2 transition and under 535 nm excitation,enhanced red down-conversion(DC)luminescence lifetime of Cr3+ due to 2E,4T2 ? 4A2 transition were realized.Both the UC and DC transition processes were found to be highly reliant on the temperature,making them a possible choice for Optical Thermometry.With least square fitting analytics,the FIR of Er3+ from thermally coupled energy states(2H11/2 and 4S3/2)produced maximum temperature sensing sensitivity values of 1.11%K-1 at 334 K and 0.66%K-1 at 275 K,respectively.Similarly,luminescence lifetime of Cr3+ attributed to the parity forbidden(2E? 4A2)and spin allowed(4T2?4A2)produced the maximum temperature sensor sensitivity value equal to 0.19%K-1 at 435 K. |
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