Synthesis, crystal structure and luminescent properties of Eu3+-activated halotungstates applied in W-LEDs

Abstract

The self-activated and Eu3+ ions activated halotungstates Ca3WO5Cl2 phosphors have been prepared by the facile solid-state reaction. The crystal structure, photoluminescence excitation (PLE) and emission (PL) spectra, temperature-dependent PLE, and decay curves were investigated. When excited by ultraviolet (UV) light, the pure Ca3WO5Cl2 shows blue emission, which can be ascribed to the typical self-activated emission of charge transfer band (CTB) transitions in [WO5Cl]5- groups. As the temperature increases from 10 to 480 K, the PL intensity decreases, and the emission band appears blue shift. The concentration dependent PL spectra of Ca3WO5Cl2:Eu3+ show several characteristic emission peaks of Eu3+ ions in the red emission region around 615 nm together with the host emission band in the blue emission region at around 450 nm. Accordingly, the broadband originates from the CT behavior in [WO5Cl]5- group, while the sharp lines originate from the 5D0-7F2 transitions in Eu3+ ions. The energy transfer process between Eu3+ and WO5Cl was discussed. All results indicate the possibility for UV to blue LED applications with multi-color emissions in a single stable host.