The effects of Eu-concentrations on the luminescent properties of SrF2:Eu nanophosphor

SrF2:Eu nanophosphors were successfully synthesized by the hydrothermal method. The structure of the nanophosphors was investigated with x-ray diffraction. The average crystallite size calculated using the Scherrer equation was in the range of 7.0 nm. The photoluminescence of Eu doped as-prepared SrF2 nanophosphors were studied using different excitation sources. The samples showed emission from both the Eu oxidation states, Eu2+ and Eu3+. At low Eu concentrations the emission from Eu2+ centered at 416 nm was more dominant. While the narrow band of Eu3+ emission intensity increased with an increase in the Eu concentration. High resolution x-ray photoelectron spectroscopy results indicated that the Eu was indeed in both Eu2+ and Eu3+ valance states. The presence of Eu2+ and Eu3+ in the system largely enhanced the response of the Eu3+ under ultraviolet excitation. The time of flight-secondary ion mass spectrometry results suggested that the energy transfer between two ions was likely to occur. The relative photoluminescence intensity of the Eu2+ rapidly decreased with an increasing laser beam irradiating time. This result would make the current Eu2+ doped SrF2 samples unsuitable candidates for several applications, such as white light-emitting diodes and wavelength conversion films for silicon photovoltaic cells.