In a few samples, we also detected a peak at ≈566 nm upon CW laser illumination (Figure ). These emissions indicate contributions from 5 D1 → 7 F2 (≈566 nm) and 5 D1 → 7 F3 (≈579 nm) transitions to the PL spectrum of the ALD/MLD films when direct excitation of the 5 D1 level occurs. Interestingly, the green emission at ≈566 nm was observed only on pristine and TPO graphene and was absent on Si and SiO2. Note that 532 nm excites the 5 D1 level and we do not consider transitions from higher energy states. When excited by a 532 nm CW laser, the intensities of the PL peaks at ≈566 nm and ≈579 nm, relative to the peak at ≈612 nm, are significantly higher for Eu-BDC on graphene compared to the 100 nm Eu-BDC film on Si, which was excited at 250 nm (Figures and). Therefore, the emission from the 5 D1 level is enhanced compared to the emission from the 5 D0 level for Eu-BDC films on pristine and TPO graphene. The 7 F0 → 5 D1 pure magnetic dipole transition, excited by a 532 nm laser, populates the 5 D1 level. One possible enhancement mechanism could be the suppression of non-radiative relaxation to the 5 D0 level, but it is difficult to identify any graphene-induced process responsible for this. Another possibility is an enhanced radiative rate from the 5 D1 state to 7 Fj, however, we are not aware of any graphene-induced mechanism behind this. A third possibility is a thermally activated enhancement of the 5 D1 state population, potentially caused by laser-induced heating of graphene. We tested this hypothesis by measuring the PL spectra at different excitation powers (Figure ), but the results did not show enhanced emission with increased power. Additionally, the PL intensity of the peak at ≈612 nm after 532 nm CW laser excitation demonstrates a linear response (Figure ), showing that no two-photon absorption processes are involved in signal generation. Thus, the mechanism behind this enhancement remains unclear.