Electrochemiluminescence behaviors of Eu3+-doped CdS nanocrystals film in aqueous solution

Eu3+ doped CdS nanocrystals (CdS:Eu NCs) were synthesized via a co-precipitation method. The doping of Eu3+ ions caused a 4-fold enhancement in electrochemiluminescence (ECL) intensity and more stable cathodic signals compared to pure CdS NCs. Such enhancement was mostly ascribed to doping-induced improvement in the stability of reduced NCs. A new emission peak around 620 nm was observed in ECL spectra of the doped NCs, which belongeded to the D-5(0) -> F-7(2) transition of Eu3+ ions in CdS NCs. Correspondingly, a pair of oxidation and reduction peaks occurred at +1.01 V and +0.61 V because of the formation of Eu3+-surface states complex when the CdS:Eu NCs solution underwent cyclic voltammogram scanning. Benefiting from the strong ECL emission of the doped NCs and high affinity of the doped Eu3+ ions to oxygen, the CdS:Eu NCs film showed a great oxygen-sensitivity. The intense red luminescence of the characteristic transitions of Eu3+ in CdS:Eu NCs would also have enormous potential in bioanlytical systems.