Research On The Thermometric Behaivor In Er³⁺ Doped Upconversion Luminescent Materials

Temperature is one of the basic physical parameters, which is crucial in scientific research, industial manufacturing, medical and daily life. Traditional thermometers are based on the principle of liquid and metal expansion, which is realized by heat flow to an invasive probe, such as mercury, alcohol, resistance and thermocouple thermometer, etc. However, the traditional temperature sensor could not meet requirements in many areas with the development of science and engineering, such as the measurement in acid corrosion environment, biological cells, electromagnetic interference environment and fast moving objects, etc. Therefore, it is necessary to develop the new temperature sensors with rapid response in some special environment. Recently, the non-contact temperature measurement technique based on the physical optical response has attracted more attention. In particular, the fluorescence intensity ratio ?FIR? technique is regarded as the most promising. In this work, we selected NaLnTiO₄:?Ln= Y, Gd? and NaLa?MoO₄?₂ as hosts and rare earth ions Yb³⁺/Er³⁺ as doping ions to develop optically temperature sensor. The sol-gel and hydrothermal methods were used to prepare a series of up-conversion ?UC? phosphors.The Yb³⁺/Er³⁺ ions co-doped NaLnTiO₄ ?Ln= Y, Gd? up-conversion ?UC? phosphors were synthesized by sol-gel method. The phase purity and the structure of the samples were characterized by powder X-ray diffraction ?XRD?, and the optimal composition was also determined according to their UC emission intensities. The obtained emission spectra consist of two green emission ?530 and 550 nm? bands and a red emission ?668 nm? band, which are assigned to 2H11/2?4I15/2,4S3/2?4I15/2 and 4F9/2?4I15/2 the characteristic inner shell transitions of Er³⁺. The UC mechanism and processes responsible for the emissions were investigated to involve two-photon absorption. The lifetime of green emission in Er³⁺ singly doped and Yb³⁺-Er³⁺co-doped were measured to prove the existence of energy transfer. Finally, the temperature-dependent fluorescence intensity ratios ?FIR? for the NaLnTiO₄:?Ln= Y, Gd? were measured, and the maximum sensitivity was approximately 0.0045 K^-1. It indicates that Yb³⁺/Er³⁺ ions co-doped NaLnTiO₄ ?Ln= Y, Gd? phosphor is potential candidates for optical temperature sensors.Yb³⁺/Er³⁺ co-doped NaLa?MoO₄?₂ up-conversion mono-disperse shuttle-like microcrystals were prepared by hydrothermal method. The phase purity, structure and morphologies of the samples were characterized by X-ray diffraction ?XRD?, field emission scanning electron microscope ?FE-SEM? and a deduction for the growth mechanism of shuttle-like microcrystals was also made. UC luminescence spectra was reseached at room temperature of phosphors annealed at 600? for 1 h and un-annealed samples with the excitation of 980 nm laser. Temperature sensing properties of NaLa?MoO₄?₂:Er³⁺/Yb³⁺ shuttle-like microcrystals without and with calcination at 600? for 1 h were investigated. The maximum sensitivity for the sample without sintering reach 0.0135 K^-1 and the maximum sensitivity reaches 0.0131 K^-1 for sample with sintering. This result indicates that the different luminescence intensity for NaLa?MoO₄?₂:Er³⁺/Yb³⁺ samples with same crystal morphology and size distribution has no remarkable effect on the value of sensitivity. In order to verify the above conclusions, a series of different doping concentrations of NaLa?MoO₄?₂:0.01Er³⁺, x Yb³⁺ were successfully synthesized by sol-gel method. The different doping concentration on temperature dependence was studied and the results show that different doping concentration has no effect on the value of the temperature sensitivity. The maximum sensitivity is higher than the values reported in literatures. Moreover, the molybdate have excellent features, such as photo electromagnetic illustrate that the micron size NaLa?MoO₄?₂:Er³⁺/Yb³⁺ can be used as a temperature sensor applied in biomedicine.