Highly Efficient Exciton Modulation in MoSe$_2$/PdSe$_2$ Heterostructures
Controlling exciton recombination in atomically thin semiconductors is central to their optoelectronic functionality, as the competition between radiative and non-radiative decay channels governs emission efficiency. Existing approaches, such as defect passivation, chemical doping, dielectric engineering, and strain tuning, primarily aim to suppress non-radiative losses. Here, we report a pronounced $\sim$6-fold enhancement of room-temperature A-exciton emission in a type-I MoSe$_2$/PdSe$_2$ van der Waals heterostructure, yielding a photoluminescence quantum yield of 6 %, compared to $\sim$1 % for as-exfoliated monolayer MoSe$_2$. This enhancement is accompanied by strong quenching of the B-exciton, consistent with interlayer electronic coupling that redistributes exciton populations toward the radiative A-exciton channel. Power- and temperature-dependent measurements reveal a suppression of exciton-exciton annihilation and a crossover to quenched emission at low temperature, indicating a redistribution of exciton relaxation pathways. Photoluminescence excitation spectroscopy further reveals a broadband enhancement spanning 450-725 nm, ruling out a resonance-specific mechanism. These results demonstrate that interlayer electronic coupling can be used as an efficient means to redirect exciton populations toward radiative channels, enhancing emission efficiency in two-dimensional semiconductors without chemical modification or strain.