Study of Sensitivity vs. Excitation Time of LED Excited Thermographic Phosphors

The rise time method is a time-resolved temperature measurement technique based on phosphorescence. Its short measurable time and high uncertainty limit its application. In this study, a long-term excitation on the millisecond level was used on the phosphor Mg 4 FGeO 6 :Mn 4+ to realize a low uncertainty rise-time-based phosphor thermometry. A 385 nm UV-LED was used as excitation light and a high-speed camera was used as the detector. The results of calibration show that Mg 4 FGeO 6 :Mn 4+ has a long rise time from 1140 ms to 2920 ms which is directly related to the temperature and has a low uncertainty of 1.2% in the temperature range of 293 K to 623 K. High absolute sensitivity of 3.02 µs K −1 was found at 623 K, and it increased with the decrease of temperature, reaching 7.65 µs K −1 at 293 K. To evaluate the effort of the excitation light on the rise time, the rise time of Mg 4 FGeO 6 :Mn 4+ was measured with different excitation time and excitation energy. The results show that the rise time of Mg 4 FGeO 6 :Mn 4+ is stable with different excitation times and decreases a little with the increase of the excitation energy. Finally, the rise time-based phosphor thermometry using Mg 4 FGeO 6 :Mn 4+ was successfully applied on a 2D temperature measurements of jet impingement cooling. This is the first time of using MFG with a long-term excitation as the rise time-based phosphor thermometry. The high sensitivity and low-uncertainty demonstrate that Mg 4 FGeO 6 :Mn 4+ has excellent performance for rise-time-based phosphor thermometry.

Section: Introductionmentioning

confidence: 99%

Rise time-based phosphor thermometry using Mg₄FGeO₆:Mn⁴⁺

Cai

Park

Mohammadshahi

et al. 2020

“…Their approach demonstrated advantages for 2D thermometry. They performed uncertainty measurements between 473 and 833 K and showed the superior performance of the dualgate method above 750 K. Westphal et al [6] conducted calibrations of Mg 3 F 2 GeO 4 :Mn for excitation times of 1, 2, 3, 4, and 5 µs, much shorter than the characteristic decay of a few milliseconds. They state results were slightly different but did not quantify or give a correlation with pulse duration.…”

Section: Introductionmentioning

confidence: 99%

On the role of excitation pulse duration on luminescence measurements

Allison¹

2021

Described here is an investigation into the effects of excitation pulse duration on the temporal character of luminescence of three characteristic thermographic phosphors: Mg4FGeO6:Mn, La2O2S:Eu, and YAG:Dy. Attention is first given to the build-up of the emission while the excitation pulse is on and its relation to temperature. Next, effects after pulse termination are addressed. For emission comprised of two or more characteristic decays, increasing the pulse duration will enhance the longer components relative to the shorter. For La2O2S:Eu, increasing the duration increases emission of successively longer-lived emitting states; and they display pronounced temperature dependence. For YAG:Dy, as excitation duration is increased, the main decay component used for thermometry is enhanced relative to two shorter components of less interest.

“…The typical source for excitation of thermographic phosphors is a laser emitting in the UV or visible range [7]. Light emitting diodes emitting in this range have also been employed for phosphor excitation [13][14][15][16]. In certain applications, however, it may be beneficial to explore the use of x-rays as an alternate source for excitation of thermographic phosphors.…”

Section: Introductionmentioning

confidence: 99%

Visible emission spectra of thermographic phosphors under x-ray excitation

Westphal

Brown

Quintana

et al. 2021

Thermographic phosphors have been employed for temperature sensing in challenging environments, such as on surfaces or within solid samples exposed to dynamic heating, because of the high temporal and spatial resolution that can be achieved using this approach. Typically, UV light sources are employed to induce temperature-sensitive spectral responses from the phosphors. However, it would be beneficial to explore x-rays as an alternate excitation source to facilitate simultaneous x-ray imaging of material deformation and temperature of heated samples and to reduce UV absorption within solid samples being investigated. The phosphors BaMgAl10O17:Eu (BAM), Y2SiO5:Ce, YAG:Dy, La2O2S:Eu, ZnGa2O4:Mn, Mg3F2GeO4:Mn, Gd2O2S:Tb, and ZnO were excited in this study using incident synchrotron x-ray radiation. These materials were chosen to include conventional thermographic phosphors as well as x-ray scintillators (with crossover between these two categories). X-ray-induced thermographic behavior was explored through the measurement of visible spectral response with varying temperature. The incident x-rays were observed to excite the same electronic energy level transitions in these phosphors as UV excitation. Similar shifts in the spectral response of BAM, Y2SiO5:Ce, YAG:Dy, La2O2S:Eu, ZnGa2O4:Mn, Mg3F2GeO4:Mn, and Gd2O2S:Tb were observed when compared to their response to UV excitation found in literature. Some phosphors were observed to thermally quench in the temperature ranges tested here, while the response from others did not rise above background noise levels. This may be attributed to the increased probability of non-radiative energy release from these phosphors due to the high energy of the incident x-rays. These results indicate that x-rays can serve as a viable excitation source for phosphor thermometry.