Fluorescent Temperature Sensing Techniques Based On The 5d-4f Broadband Emission Of Rare-earth Ions

Temperature plays an important role in the optical properties of phosphors. Such fluorescent temperature sensing has attracted more and more attention in the fields of biochemistry, power industry, and so on. Traditional fluorescent temperature sensing techniques mainly include fluorescence intensity, fluorescence intensity ratio（FIR） and fluorescence lifetime（FL） methods. The bandwidth and peak wavelength are also temperature-sensitive.In this article, various fluorescent temperature sensing techniques were summarized and compared. We developed two novel ratio-metric sensing techniques with broadband fluorescence offering the sensing signals. The techniques named selfreferenced intensity ratio technique and integral intensity ratio technique behave similarly like the traditional FIR technique. Furthermore, a new factor- barycenter energy of the emission band- was introduced to locate the band position for sensing purpose. Compared with the peak shift characterization, the precision of sensing was highly improved.Four phosphors with broadband emission have been studied as temperature sensor with above mentioned techniques. The findings are:（1） Yellow phosphor YAG:Ce³⁺: While the bandwidth narrows down with an increasing temperature, the band shifts towards red. The sensing equations were decided as Y = 17583- 0.98 X（barycenter）, Y = 32- 0.04 X（intensity ratio I（564nm）/I（684nm）） and Y = 1.2- 0.003 X（integral intensity ratio）. The repeatability and hysteresis characteristics were also investigated.（2） Green phosphor（Ba,Sr）₂SiO₄:Eu²⁺: While the bandwidth broadens with an increasing temperature, the band shifts towards red. The sensing equations were decided as Y = 19005- 0.15 X（barycenter）, Y = 72- 0.32 X（intensity ratio I（525nm）/I（465nm）） and Y = 1.0 + 0.0003 X（integral intensity ratio）.（3） Red phosphor Sr Si Al N3:Eu²⁺: While the bandwidths broadens with an increasing temperature, the band shifts towards blue. The sensing equations were decided as Y = 16741 + 1.35 X（barycenter）, Y = 2.5- 0.004 X（intensity ratio I（594nm）/I（634nm）） and Y = 0.8 + 0.003 X（integral intensity ratio）.（4） Blue phosphor Sr4Al14O25:Eu²⁺,Dy³⁺: while the bandwidths broadens with increasing temperature, the band shifts towards red. The sensing equations were decided as Y = 20013- 1.15 X（barycenter）, Y = 25- 0.07 X（intensity ratio I（495nm）/I（575nm）） and Y = 1.3 + 0.003 X（integral intensity ratio）.As a real application, we put forward to a differential fluorescent temperature sensing at the end of the text. Two temperature points can be monitored with fluorescent methods simultaneously in a single emission spectrum. The blue and red phosphors were selected as an example.