Dual functionality luminescence thermometry with Gd2O2S:Eu3+,Nd3+ and its multiple applications in biosensing and in situ temperature measurements.

Luminescence thermometry using sharp line emission of lanthanide ions has become an active area of research as it offers the advantages of remote temperature sensing with high sensitivity and superior spatial resolution. The most widely applied method relies on the temperature dependence of the luminescence intensity ratio of emission lines from two thermally coupled levels. However, the usable temperature range for this type of Boltzmann thermometer is limited. In addition, the weak and narrow line absorption of the parity forbidden 4f-4f transitions of lanthanides forms a serious drawback. To solve both problems, we here report a new dual functionality luminescence thermometer: Gd2O2S co-doped with Eu3+ and Nd3+. This material combines Boltzmann and energy transfer thermometry to extend the temperature range and uses the strong and broad charge transfer absorption band of Eu3+ for sensitization. In the T-range of 300-500 K efficient energy transfer from Eu3+ to Nd3+ allows for charge transfer-sensitized luminescence thermometry using near infrared emission from the thermally coupled 4F3/2 and 4F5/2 levels of Nd3+. Above 500 K a high temperature sensitivity is obtained using the strong temperature dependence of the luminescence intensity ratio of red Eu3+ to near infrared Nd3+ emission. The dual-functionality provides a single thermometer combining strong absorption and high relative sensitivity (0.6 - 1.4%) over a wide temperature range (300 to 650 K). Finally, it is proposed that this dual-function luminescent thermometer has promising potential for multifunctional applications in biosensors and in situ temperature measurements of chemical reaction process.