Energy transfer between WO42- groups and Eu3+ in CaWO4：Eu3+ phosphor

Abstract

The pure CaWO4 and 1%Eu3+ doped CaWO4 phosphors are successfully prepared by the conventional solid state reaction method. The photoluminescence (PL) spectra, decay cures, and time-resolved PL spectra are measured at depend on different temperatures. Fluorescence spectra at room temperature (300 K) and low temperature (10 K) show that these two samples each have a broad band at about 430 nm, originating from the WO42- groups under 240 nm excitation, while the CaWO4:Eu3+sample exhibits the characteristic emission of Eu3+ corresponding to 5D0→7F1, 2, 3,4 transitions due to the absorbed energy transfer from WO42- groups to Eu3+ ions. And the red light at 616 nm of CaWO4: Eu3+ can be excited efficiently by UV (395 nm) and blue (465 nm) light. The decay curves at 300 K illustrate that the lifetime of WO42- group in pure CaWO4 is about 8.85 s but is shortened to 6.27 μs after Eu3+ions have been doped, which is a further good evidence for demonstrating the existence of WO42-–Eu3+ energy transfer process. The energy transfer efficiency (ηET)) and rate (ωET) between WO42- and Eu3+in CaWO4: 1%Eu3+ are 29.2% and 4:65×104 s-1 respectively, when T = 300 K. The energy transfer process is studied in detail by the time-resolved PL spectra, and the lifetime for the appearance of Eu3+ emission in CaWO4 decreases monotonically as temperature increases from 10 K to 300 K. The temperature dependence of luminescence decay time is performed and the results indicated that the lifetime of Eu3+ increases in a temperature range of 10-50 K, when the temperature is more than 50 K, thermal quenching of Eu3+ begins and the lifetime is shortened. However, the lifetime of WO42- reduces constantly with the increase of temperature.