Songtao Guo's research while affiliated with Shanghai Jiao Tong University and other places

In this study, the effect of oxygen partial pressure on phosphorescence was investigated for different lanthanide ion-doped (Ln = Eu, Dy, Sm, Er) yttria-stabilized zirconia (YSZ). Samples of YSZ powders doped with 1 mol% Ln³⁺ were prepared using the sol-gel method. A measurement system comprising a pressure and temperature calibration chamber, a 405 nm laser, a spectrometer, a photo-multiplier tube (PMT) and related optics was established. The phosphor emission spectra were measured first to verify the sample fabrication method. Then, the phosphorescence lifetime of the Ln³⁺-doped YSZ (YSZ:Ln) were obtained at different oxygen partial pressures and temperatures. These data showed that all the YSZ:Ln aside from the YSZ:Er exhibited a negative correlation between phosphorescence lifetime and oxygen partial pressure in high-temperature environments. The oxygen sensitivity was enhanced as temperature increased, and further analysis showed that this oxygen sensitivity was related to the energy levels of the phosphor‘s excited state and charge transfer state. That is, an excited state at a high energy level and a change transfer state at a low energy level would lead to oxygen sensitivity. These findings not only provide a useful reference for the evaluation of the oxygen effect on YSZ:Ln³⁺-based phosphor thermometry but may also serve as a basis for developing optical pressure sensors suitable for high-temperature environments.

The quantitative relationship between stress and mechanoluminescence (ML) intensity ratio in an elastic domain was established in SrAl2O4:Eu²⁺, Dy³⁺ (SAOED) resin samples. The stress on the resin sample (macro stress) was directly measured and the stress on the SAOED (micro stress) was calculated by the Eshelby method. The macro and micro stresses keep a linear relationship, and the ML intensity ratio is proportional to stress. Even though the relationship between macro stress and ML intensity ratio is dependent on SAOED concentration and the elastic modulus of the matrix, a universial relationship exists between the micro stress and ML. Based on these results, a generalized equation, which could describe the relationship between the stress, ML intensity and ML sensor matrix, was established, which can then be applied in situations of different SAOED concentrations or even different matrix materials. This generalized relationship could provide guidance for the development and application of SAOED-based ML sensors.

This study examined the effect of ambient pressure on the luminescent lifetime of Mg4FGeO6:Mn phosphors in different morphologies. To evaluate the pressure sensitivity of phosphor in the form of particle, agglomerated particle and chemically bonded coating, samples including phosphor powder, pressed phosphor disc, and chemically bonded phosphor coating were fabricated and calibrated using a PMT-based measurement system for a pressure range of 20-200 kPa and a temperature range of 298-873 K. The results showed no obvious pressure effect on the lifetime of the chemically bonded Mg4FGeO6:Mn coating. However, the lifetime of the phosphor powder and pressed phosphor disc decreased as pressure increased. This pressure effect was most obvious for the pressed phosphor disc, which was further aggravated at higher temperatures. The atomic distance between manganese ion and other atomics reduced as pressure increased, which induced the movement of excited state in the configuration coordinate. Considering this dependency of pressure sensitivity on phosphor morphology, it is important to adopt the same fabrication procedure for calibration and temperature measurement using Mg4FGeO6:Mn. In addition, for in-flow measurement using Mg4FGeO6:Mn tracer particles, the influence of environmental pressure must be considered.

A novel pressure-sensitive paint has been developed by mixing phosphor Sr4Al14O25:Eu,Dy with pressure-sensitive luminophore PtTFPP in a polyethylene binder. The phosphor particles served as hostsforPtTFPPmoleculeswhileprovidingexcitationlightviatheirbrightblue/greenluminescence. The unique long afterglow of Sr4Al14O25:Eu,Dy allows the coating to be charged by a light source (UV-LED or even sunlight) in advance, and then the luminescent signals can be collected by using a colorcameraforpressuremeasurement(withoutanexternallightsource).Thepersistentluminescence and the pressure-sensitive signal correspond to the green and red channels, respectively. The errors due to time-varying persistent luminescence can be removed by taking an intensity ratio between the two channels. The current formulation of this light-charged pressure-sensitive paint (LC-PSP) has been optimized for the maximum signal level. It showed similarQ2 pressure sensitivity to typical pressure-sensitive paints (PSPs), and its capability was demonstrated through a nitrogen jet impingementexperiment.Thislight-chargedPSPcanbetrulyfreeoflightsourceduringmeasurement,which greatly simplifies the optical system and avoids errors due to the inconsistent illumination field, and thus provides a solution for PSP applications in facilities with limited optical access.

The mechanoluminescent (ML) sensor is a newly developed non-invasive technique for stress/strain measurement. However, its application has been mostly restricted to qualitative measurement due to the lack of a well-defined relationship between ML intensity and stress. To achieve accurate stress measurement, an intensity ratio model was proposed in this study to establish a quantitative relationship between the stress condition and its ML intensity in elastic deformation. To verify the proposed model, experiments were carried out on a ML measurement system using resin samples mixed with the sensor material SrAl2O4:Eu2+, Dy3+. The ML intensity ratio was found to be dependent on the applied stress and strain rate, and the relationship acquired from the experimental results agreed well with the proposed model. The current study provided a physical explanation for the relationship between ML intensity and its stress condition. The proposed model was applicable in various SrAl2O4:Eu2+, Dy3+-based ML measurement in elastic deformation, and could provide a useful reference for quantitative stress measurement using theMLsensor in general.