White colour emission from BaHfO3:Eu phosphor

Eu-doped barium hafnate powders, BaHfO3:Eu, prepared with ceramic method have quite peculiar spectroscopic properties, which can be significantly altered changing the dopant concentration as well as preparation atmosphere. When synthesis is performed in a reducing atmosphere, a fraction of Eu gets reduced and produces a broad-band emission peaking around 480 nm. Due to a partial overlapping of the excitation spectra of Eu3+ and Eu2+ luminescence, the emission colour can vary between bluish green, when only Eu2+ is excited, red when solely Eu3+ is stimulated and white upon simultaneous excitation of both Eu3+ and Eu2+ activator ions around 290 nm. Upon X-ray excitation only Eu3+ luminescence is produced. Radioluminescence of undoped BaHfO3 consists of a broad-band peaking around 410 nm, which disappears when Eu enters the host. Materials prepared in a reducing atmosphere do not show any phase separation even for higher Eu concentrations.