Luminescent Thermometer Systems Dy3+/Eu3+ and Tb3+/Sm3+ Based on Coordination Compounds: New Pairs to the Approved Tb3+/Eu3+?

This work addresses a comprehensive study of six new complexes of the constitution [Ln(MeDPQ)(2)Cl-3] (Ln(3+) = Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, and Y3+; MeDPQ-2-methyldipyrido-[3,2-f:2 ',3 '-h]-quinoxaline) with good thermal stability up to 446 degrees C. Statistical substitution of Sm3+, Tb3+, Gd3+, and Dy3+ with a second Ln(3+) ion led to [Ln(1-x)Ln '(x)(MeDPQ)(2)Cl-3] solid solutions, which exhibit temperature-dependent luminescent properties. Their visible emission and intensity ratios of transitions vary with temperature in the range of 253-353 K. In the case of the composition [Tb1-xEux(MeDPQ)(2)Cl-3], the maximum relative thermal sensitivity S-r values were determined as 3.77% K-1, 3.97% K-1, and 3.97% K-1 for x(Eu3+) = 0.01, 0.05, and 0.1, respectively. The compositions [Dy1-xEux(MeDPQ)(2)Cl-3] and [Tb1-xSmx(MeDPQ)(2)Cl-3] also showed significant performance. For the pair Dy3+-Eu3+, the S-r values were determined as 3.88%K-1, 3.91% K-1, and 3.80% K-1 for x(Eu) = 0.01, 0.05, and 0.1, respectively. For the pair Sm3+-Tb3+, the S-r values are 3.28% K-1 and 3.82% K-1 for x(Sm) = 0.9 and 0.1, respectively. The largest thermal sensitivity value S-r of 4.11% K-1 was achieved for the composition [Gd0.8Tb0.18Eu0.02(MeDPQ)(2)Cl-3]. In addition, patterns of thermometric performance are bound to the energy transfer efficiency Tb3+ -> Eu3+, Dy3+ -> Eu3+ -> Dy3+, and Tb3+ -> Sm3+, as this characteristic is strongly temperature-dependent in the studied range.