Beyond the Energy Gap Law: The Influence of Selection Rules and Host Compound Effects on Nonradiative Transition Rates in Boltzmann Thermometers

Apart from the energy gap law, control parameters over nonradiative transitions are so far only scarcely regarded. In this work, impact of both covalence lanthanoid–ligand bond and varying distance on magnitude intrinsic decay rate between excited 6P5/2 6P7/2 spin–orbit levels Gd3+ is investigated in chemically related compounds Y2[B2(SO4)6] LaBO3. Analysis temperature-dependent luminescence spectra reveals that transition rates 6PJ ( J = 5/2, 7/2) order 10 ms−1 (Y2[B2(SO4)6]:Gd3+: 8.9 ms−1; LaBO3:Gd3+: 10.5 ms−1) differ due to different degree GdO bonds two compounds. Comparison established luminescent Boltzmann thermometer Er3+ reveals, however, three orders slower despite a similar presence single resonant phonon mode. This hints fundamental magnetic dipolar character coupling Gd3+. These findings can pave way how tune dynamic range thermometers.