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Principle of Fluorescence Lifetime Temperature Measurement
After being irradiated with light, the electrons in the sensitive material absorb photons and transition from low energy level to excited state high energy level, and then return to low energy level through radiation transition, emitting fluorescence. The sustained fluorescence emission after the excitation light is eliminated depends on the lifetime of the excited state. This emission typically decays exponentially, and the time constant of exponential decay can be used to measure the lifetime of the excited state, which is called the fluorescence lifetime or fluorescence decay time.
Fluorescence lifetime temperature sensor
The length of fluorescence lifetime depends on the temperature. Fluorescence lifetime temperature sensors emit linear spectra in the visible spectrum after certain rare earth fluorescent substances are irradiated and excited by ultraviolet light, که, fluorescence and its afterglow are the luminescence after the excitation stops. If a parameter of fluorescence is modulated by temperature and the relationship is monotonic, this relationship can be used for temperature measurement. The intensity of the linear spectrum is related to the intensity of the excitation light source and the temperature of the fluorescent material. If the light source is constant, the intensity of the fluorescent linear spectrum is a single value function of temperature and decays over time. Generally, the lower the external temperature, the stronger the fluorescence and the slower the decay of afterglow. By filtering out the excitation spectrum through a filter and measuring the intensity of the fluorescence afterglow emission spectral lines, the temperature can be determined. But this measurement method requires stable excitation light intensity and signal channel, which is difficult to achieve, so it is rarely used. به علاوه, the decay time constant of fluorescence afterglow is also a single value function of temperature.
From the perspective of semiconductor theory, the decay and disappearance of afterglow is the quenching process of light. The higher the temperature, the stronger the lattice vibration, the more phonons participate in absorption, and the faster the light quenching. بنابراین, the temperature of fluorescent materials determines the speed of light quenching, که, the size of the decay time constant.
The biggest advantage of using fluorescence lifetime for temperature measurement is that the temperature conversion relationship is determined by the fluorescence lifetime, and is not affected by other external factors such as changes in excitation light source intensity, fiber transmission efficiency, or coupling degree. بنابراین, it has significant advantages over the temperature measurement method using fluorescence peak intensity or intensity ratio as the temperature sensing signal, and is based on the principle of fiber optic temperature measurement.
