A new class of luminescent nanoprobes based on main-group Sb³⁺ emitters

Inorganic luminescent nanocrystals (NCs) doped with main-group ns²-metal ions have evoked tremendous interest in many technological fields owing to their superior optical properties. Herein, we report a new class of luminescent nanoprobes based on 5s²-metal Sb³⁺-doped CaS NCs that are excitable by using a near ultraviolet light-emitting diode. The optical properties and excited-state dynamics of Sb³⁺ in CaS NCs are comprehensively surveyed through temperature-dependent steady-state and transient photoluminescence (PL) spectroscopies. Owing to the strong electron–phonon coupling of Sb³⁺ in CaS NCs, Sb³⁺ ions experience a dynamic Jahn-Taller distortion on the excited state, which results in bright green PL of Sb³⁺ with a broad emission band, a large Stokes shift, and a high PL quantum yield up to 17.3%. By taking advantage of the intense PL of Sb³⁺, we show in proof-of-concept experiments the application of biotinylated CaS: Sb³⁺ NCs as sensitive luminescent nanoprobes for biotin receptor-targeted cancer cell imaging and zebrafish imaging with a high imaging contrast. These findings provide fundamental insights into the excited-state dynamics of Sb³⁺ in CaS NCs, thus laying a foundation for future design of novel and versatile luminescent nanoprobes via main-group ns²-metal doping.