New Family of Luminescent Tetranuclear Lanthanide-Based Germsesquioxanes: Luminescence and Temperature Sensing

We report the synthesis, structures, magnetic, and luminescence properties of a new series of tetranuclear lanthanide-based germsesquioxanes [NEt 4 ] 2 [(Ph 4 Ge 4 O 8 ) 2 (Ln 4 )(NO 3 ) 6 (EtOH) 2 (MeCN) 2 ]· n (CH 3 CN) (where Ln = Eu 3+ ( 1 ), Tb 3+ ( 2 ), Tb 3+ /Eu 3+ ( 3 ), Dy 3+ /Y 3+ ( 4 ), and Dy 3+ ( 5 )). These paramagnetic compounds exhibit characteristic Ln 3+ -based emission in solid state at room and liquid nitrogen temperature. Temperature-dependent luminescence investigated between 293 and 373 K reveals that mixed Tb 3+ /Eu 3+ ( 3 ) compound works as a self-referenced ratiometric optical thermometer with a maximum relative sensitivity of 0.87%·°C –1 achieved at 57.6 °C.