Novel erbia-yttria co-doped zirconia fluorescent thermal history sensor

Abstract

Thermochromic pigments are commonly used for off-line temperature mapping on components from systems operating at a temperature higher than 1073 K. However, their temperature resolution is often limited by the discrete number of color transitions they offer. This paper investigates the potential of erbia-yttria co-doped zirconia as a florescent thermal history sensor alternative to thermochromic pigments. Samples of yttria-stabilized zirconia powder (YSZ, 8.3 mol% YO 1.5) doped with 1.5 mol% ErO 1.5 and synthesized by a sol-gel route are calcined for 15 minutes under isothermal conditions between 1173 and 1423 K. The effects of temperature on their crystal structure and room temperature fluorescence properties are then studied. Results show a steady increase of the crystallinity of the powders with temperature, causing a significant and permanent increase of the emission intensity and fluorescence lifetime which could be used to determine temperature with a calculated theoretical resolution lower than 1 K for intensity. The intensity ratio obtained using a temperature insensitive YSZ:Eu 3+ reference phosphor is proposed as a more robust parameter regarding experimental conditions for determining thermal history. Finally, the possibilities for integrating this fluorescent marker into sol-gel deposited coatings for future practical thermal history sensing applications is also discussed.

On the thermal sensitivity and resolution of a YSZ:Er3+/YSZ:Eu3+ fluorescent thermal history sensor

“…YSZ:Er 3+ powder of composition (YO 1.5 ) 0.083 (ErO 1.5 ) 0.015 (ZrO 2 ) 0.902 and YSZ :Eu 3+ powder of composition (YO 1.5 ) 0.078 (EuO 1.5 ) 0.02 (ZrO 2 ) 0.902 were synthesized by a sol-gel route using the protocol described in reference [27]. Samples of the YSZ:Er 3+ powder, in a partially crystalline state after calcination at 973 K for two hours, were further annealed for 15 min under isothermal conditions at various temperature between 1173 K and 1423 K with 50 K steps.…”

“…The YSZ:Eu 3+ powder, also in a partially crystalline state after calcination at 973 K for two hours, was simply annealed for 2 h at 1373 K to ensure full crystallization [27], as this phosphor was selected to play the role of a reference with little sensitivity of its fluorescence emission properties to thermal history when further calcined for 15 min between 1173 K and 1423 K.…”

“…Over the last few years, the Institut Clément Ader has been developing YSZ phosphors and coatings prepared by a sol-gel route for high temperature sensing in thermal barrier coatings, such as YSZ:Eu 3+ and YSZ:Er 3+ [24][25][26]. In particular, the latter was found to be a suitable candidate for thermal history sensing [27]: the continuous enhancement of crystallinity of YSZ:Er 3+ powders produced by a sol-gel route with temperature for 15 min long heat treatments between 1173 K and 1423 K induced substantial and consistent increases of their green emission intensity and fluorescence decay time in the ranges 1223 K-1423 K and 1173 K-1373 K respectively [27]. As shown in Fig.…”

“…1. Evolution of the relative intensity increase of the fluorescence emission of a sol-gel synthesized YSZ:Er 3+ powder with the temperature of exposure after 15 min long heat treatments [27]. The position of the main emission peaks of YSZ:Eu 3+ , which could be used as a reference because of its little sensitivity to temperature of exposure when fully crystallized, is also indicated.…”

“…In particular, the interest of this YSZ:Er 3+ /YSZ:Eu 3+ coating is discussed in the view of the physical properties of sol-gel deposited YSZ coatings, the selection of an appropriate excitation wavelength and the practical measurement of coatings fluorescence properties. The sensitivity and the resolution of a hybrid YSZ:Er 3+ /YSZ:Eu 3+ phosphor for both an intensity ratio and lifetime analysis based approaches, determined from temperature calibration curves from earlier work [27], are investigated and compared with standard methods for measuring temperature.…”