Well-tuned white-light-emitting behaviours in multicenter-Ln polyoxometalate derivatives: A photoluminescence property and energy transfer pathway study.

Abstract

White light-emitting diodes (WLEDs) are of scientific significance in terms of their wide applications, and few uminescent materials based on white-light-emitting polyoxometalate (POM) derivatives have been reported till now. Herein, a series of organic chromophores modified POM derivatives [N(CH3)4]3K2Ln(C7H5O2)(H2O)2(α-PW11O39)]·11H2O (Ln3+ = Eu3+ (1), Tb3+ (2), Tm3+ (3), Lu3+ (4)) and multicenter-Ln analogues [N(CH3)4]3K2EuxTbyTm1-x-y(C7H5O2)(H2O)2(α-PW11O39)·11H2O (5-11) were synthesized successfully and were characterized by various physico-chemical analysis. The investigations indicate the white-light-emitting behavior can be well tuned by adjusting the molar ratio of Eu3+/Tb3+/Tm3+ = 0.06:0.10:0.84 in 9. The energy transfer process from organic benzoic and POM ligands to Eu3+, Tb3+ and Tm3+ emitting centers were detected through time-resolved emission spectroscopy (TRES) and the comparison of excitation of single-, double-, treble-Ln3+ mixed, indicating the energy can transfer from the photoexcitation O → M LMCT state of POM components and π → π* transition of organic ligand to sensitize the emissions of Ln3+ ions via intramolecular energy transition mechanism. The energy transfer between Eu3+ and Tb3+, Tm3+ and Eu3+, Tm3+ and Tb3+ ions also have been recorded and carefully studied by TRES and variations of Tm3+ luminescence lifetime in this context, and the results show a low-effectively process of energy transfer between Tm3+/Eu3+, Tm3+/Tb3+ ions and a relatively good energy transfer efficiency between Eu3+/Tb3+ ions.