Electro-Optical Evaluation of Cu ¹⁺ and Cu ²⁺ States in Copper-Doped CdSe Colloidal Quantum Wells

Resolving the ambiguous oxidation state of copper dopants responsible for the large Stokes-shifted emission in CdSe colloidal quantum wells (CQWs) is critical for harnessing their emerging optoelectronic properties. Employing carrier injection to tune the population distribution between Cu1+/Cu2+ centers and in situ monitoring of the copper-related emission (CE), we have revealed that the CE band undergoes blueshifting, intensity quenching, and line width broadening with gradually increased Cu2+ states. Time-resolved CE dynamics and intragap absorption further confirm that Cu2+ states generate narrow, inefficient emission with minimal Stokes shifts due to trap-mediated Auger recombination, reduced radiative center energy spanning, and Fermi-level shifts. Accordingly, we identify Cu1+ as the dominant species that produces the bright, broad CE band with its hallmark large Stokes shift. This work not only presents mechanistic clarifications but also provides an effective approach to electrically modulate defect emissions in CQWs.