Abstract
Optical thermometry based on the up-conversion intensity ratio of thermally coupled levels of rare earth ions has been widely studied to achieve an inaccessible temperature measurement in submicron scale. In this work, a novel optical temperature sensing strategy based on the energy transfer from charge transfer bands of W-O and Eu-O to Eu3+-Dy3+ ions is proposed. A series of Eu3+/Dy3+ co-doped SrWO4 is synthesized by the conventional high-temperature solid-state method. It is found that the emission spectra, emission intensity ratio of Dy3+ (572 nm) and Eu3+ (615 nm), fluorescence color, lifetime decay curves of Dy3+ (572 nm) and Eu3+ (615 nm), and relative and absolute sensitivities of Eu3+/Dy3+ co-doped SrWO4 are temperature dependent under the 266 nm excitation in the temperature range from 11 K to 529 K. The emission intensity ratio of Dy3+ (572 nm) and Eu3+ (615 nm) ions exhibits exponentially relation to the temperature due to the different energy transfer from the charge transfer bands of W-O and Eu-O to Dy3+ and Eu3+ ions. In this host, the maximum relative sensitivity Sr can be reached at 1.71% K−1, being higher than those previously reported material. It opens a new route to obtain optical thermometry with high sensitivity through using down-conversion fluorescence under ultraviolet excitation.
Highlights
White light emitting diode (LED) technology has attracted much attention in the solid-state lighting industry, due to the advantages of white LEDs including power saving, long lifetime, and environmental benefit[1,2,3]
Zhou reported that the emission intensity ratio of 5D1 to 5D0 of Eu3+-doped transparent MF2 (M = Ba, Ca, Sr) glass ceramics increased with the temperature increase[12]
Compared with the pure SrWO4, the diffraction peaks of the Eu3+, Dy3+ single-doped and Eu3+/Dy3+co-doped SrWO4 exhibit a slight shift toward high-angle side, due to substitution of Sr2+ (1.26 Å, CN = 8) ions by smaller size Dy3+ (1.03 Å, CN = 8) and Eu3+ (1.07 Å, CN = 8) ions, which revealing that Dy3+ and Eu3+ ions have been successfully doped into the system[18, 19]
Summary
White light emitting diode (LED) technology has attracted much attention in the solid-state lighting industry, due to the advantages of white LEDs including power saving, long lifetime, and environmental benefit[1,2,3]. Das and co-authors reported the controllable white light emission from Dy3+-Eu3+ co-doped KCaBO3 phosphor[6]. Laguna reported the shape controlled white light emission from Dy3+-Eu3+ co-doped CaMoO4 microarchitectures[7]. Hirai obtained the white light emission from Dy3+-Eu3+ co-doped Sr2CeO48. Zhou reported that the emission intensity ratio of 5D1 to 5D0 of Eu3+-doped transparent MF2 (M = Ba, Ca, Sr) glass ceramics increased with the temperature increase[12]. The temperature dependent optical property of Dy3+-Eu3+ co-doped materials has not been studied so far. It is necessary to explore the spectra and energy transfer of Dy3+-Eu3+ co-doped materials at high temperature. It is observed that the fluorescence intensity ratio between Eu3+ and Dy3+ emissions are strongly dependent on the temperature at the temperature range from 11 K to 529 K. The Eu3+/Dy3+ co-doped SrWO4 phosphors are proved as an excellent materials used for optical thermometry, due to its maximum value of Sr as high as 1.71% K−1
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