Abnormal Blueshift of Mn d−d Emission Unlocked by Decreasing Phonon Coupling under High Pressure

Mn d-d emission has been a star transition-metal activated phosphors that were extensively used in optoelectronic devices. However, due to the complex and elusive luminescence mechanism, the full potential of this material remains largely untapped. Here, we designed a core-shell structure of MnS@CdS quantum dots (QDs) to investigate the effect of the internal strain on the Mn emission. Upon pressure processing, an unexpected blueshift of Mn emission was achieved. When the pressure reached a pressure of 2.1 GPa, the conventional redshift of Mn emission reappeared. Remarkable color transition from red to orange and then back to red was observed during pressure treatment. Further analysis revealed that the application of external pressure facilitated the diffusion of Mn atoms into the CdS shell, strengthened host-dopant coupling and mitigated the lattice mismatch rate within the MnS@CdS QDs. These factors resulted in a reduction in phonon coupling strength and an increase in energy transfer efficiency from the exciton of the CdS host lattice to the Mn dopants, thus ultimately accounting for the abnormal blueshift of Mn d-d emission. Our findings represent a significant breakthrough in the quest for precise control and regulation of Mn-related emission, offering insights into the underlying luminescence mechanism of Mn emission.