Anomalous preparation, intense 5D0 → 7F4 emission and adjustable double center emission of Eu3+ and Eu2+ codoped Ca2Al2SiO7

A series of Eu3+ /Eu2+ codoped Ca2Al2SiO7 were synthesized by traditional solid-state synthesis in reducing atmosphere. In this work, XRD powder diffraction proved that the obtained sample was pure. Photoluminescence properties are characterized by excitation, emission spectra and decay curves. Double center emission is achieved by adjusting excitation wavelength and concentration. Under the 394 nm excitation, the emission spectra Ca2Al2SiO7: Eu phosphors exhibit two bands situated at blue emission of 4f5d-4f transition from Eu2+ ion and red emission of 4f-4f transition coming from Eu3+ ion. The red and yellow light can be obtained when the concentration of doped europium ions is at 0.5% and 1%, respectively. When the excitation wavelength was 394, 280 and 584 nm, the emission color change from yellow to blue, respectively. The bond energy theory explains Eu2+ and Eu3+ ion occupy Cal site in the Ca2Al2SiO7 lattices. In addition, the spectra show that the abnormal intensity peaks of europium ion at 701 nm can be found. Analysis of the related intensity D-5(0)-F-7(2)(618 nm) transition peak is similar to that of D-5(0)-F-7(4)(701 nm) transition peak in the emission spectra with the Judd-Ofelt theory.