Fig. 7: Temperature-dependent Boltzmann populations.

Boltzmann populations of the Kramer’s doublets of 4F3/2 (\(\Gamma\) and \(\Gamma^{\prime}\)) for 6Nd, showing the population distribution without considering the anti-thermal quenching effect (empty symbols) where the sum of populations is constant, and with the anti-thermal quenching effect, which causes an increase in the overall 4F3/2 population with temperature (full symbols). The trend is consistent with the observed in Fig. S8e.