Boosting the Er³⁺1.5 μm Luminescence in CsPbCl₃Perovskite Nanocrystals for Photonic Devices Operating at Telecommunication Wavelengths

CsPb(Cl1-xBrx)3 perovskite nanocrystals (NCs) doped with Yb3+ ions have recently attracted large attention for their applications in photovoltaics in view of the high quantum yield, exceeding 100% of Yb3+ emission at ∼1 μm. In contrast, the particularly relevant Er3+ emission at 1.5 μm in the third telecommunication window, of high interest in silicon integrated photonics, has been so far largely neglected in view of the weak emission performance displayed by Er3+-doped NCs. Comprehensive steady-state and time-resolved spectroscopic measurements provide insights into the underlying mechanisms of Yb3+ and Er3+ sensitization to rationalize the anomalous different behavior of these two emitters in singly doped NCs. We propose that single-photon excitation of two Yb3+ ions possibly occurs through a transient internal redox mechanism in the perovskite host, while this pathway is unviable for Er3+. In turn, Yb3+-bridged Er3+ sensitization, boosts the Er3+ luminescence at ∼1.5 μm by 104-fold compared to Er3+ singly doped NCs, and a relative high quantum yield of ∼6% and extremely long lifetime (∼3 ms) are obtained. The resulting high Er3+ excited state densities, combined with the large absorption cross-sections of the semiconducting CsPbCl3 matrix make Er3+-doped perovskite promising innovative materials to realize photonic devices operating at telecommunication wavelengths.