Role of electron transfer in Ce3+ sensitized Yb3+ luminescence in borate glass

Abstract

In a Ce[3+]-Yb[3+] system, two mechanisms are proposed so far namely, the quantum cutting mechanism and the electron transfer mechanism explaining Yb[3+] infrared luminescence under Ce[3+]excitation. Among them, the quantum cutting mechanism, where one Ce[3+] photon (ultraviolet/blue) gives rise to two Yb[3+] photons (near infrared) is widely sought for because of its huge potential in enhancing the solar cell efficiency. In present study on Ce[3+]-Yb[3+] codoped borate glasses, Ce[3+]sensitized Yb[3+] luminescence at ∼1 μm have been observed on Ce[3+] 5d state excitation. However, the intensity of sensitized Yb[3+] luminescence is found to be very weak compared to the strong quenching occurred in Ce[3+] luminescence in Yb[3+] codoped glasses. Moreover, the absolute luminescence quantum yield also showed a decreasing trend with Yb[3+] codoping in the glasses. The overall behavior of the luminescence properties and the quantum yield is strongly contradicting with the quantum cutting phenomenon. The results are attributed to the energetically favorableelectron transfer interactions followed by Ce[3+]-Yb[3+] ⇌ Ce[4+]-Yb[2+] inter-valence charge transfer and successfully explained using the absolute electron binding energies of dopant ions in the studied borate glass. Finally, an attempt has been presented to generalize the electron transfer mechanism among opposite oxidation/reduction property dopant ions using the vacuum referred electron bindingenergy (VRBE) scheme for lanthanide series.