Temperature dependence of temperature sensitive luminophores at cryogenic temperatures

In the present study, the temperature dependence of luminescence properties of 9 different metal complex temperature sensitive luminophores (Eu(hfc)3, Eu(tfc)3, EuTTA, Ru(phen)3, Ru(dpp)3, PtTFPP, PtOEP, PdTFPP, PdOEP) were investigated at cryogenic temperatures (0 °C ~ -190 °C). Luminescence was excited by the third harmonics of a pulsed Nd:YAG-laser (355 nm) and recorded by a compact size CMOS spectrometer. The luminescence decay after excitation was detected by a photodiode and temporally recorded by an oscilloscope. Common to all investigated luminescent materials, the emission intensity tended to increase as the temperature decreased. It was found that the emission intensity was extremely high, and temperature measurement with a high signal-to-noise ratio was achievable, because there was no noise caused by radiated heat at cryogenic temperatures. The rate of change in emission intensity at the peak wavelength of the emission spectrum of all luminophores, while temperature changed from 0 °C to -190 °C, exceeds 100 %. Two-color ratiometric method, which uses the ratio of integral of relative intensity at two wavelength bands, can also be applied for high precision temperature determination by some of these luminophores. The investigated luminescent materials with particularly high temperature sensitivity for two-color ratiometric method were Ru(phen)3 and Ru(dpp)3. The tested luminophores, which are suitable for the lifetime-based method, were Eu(hfc)3, Eu(tfc)3, EuTTA and PtTFPP.