Spectroscopic Characterization of Ca3Y2Si3O12:Eu2+,Eu3+ Powders in VUV-UV–vis Region

Ca3Y2Si3O12 powders activated with Eu (0.1–25%) were prepared by means of ceramic method. Their spectroscopic properties in VUV-UV–vis region were investigated. Luminescence measurements indicated that Ca3Y2Si3O12 prepared in a strongly reducing atmosphere of 20%N2–80%H2 mixture contained both Eu2+ and Eu3+ ions, and both were able to generate their characteristic emissions. A superposition of the broad band luminescence of Eu2+ and narrower 4f → 4f luminescent features of Eu3+ upon excitation with 395 nm light-emitting diode covered almost the whole visible part of spectrum. The ratio between Eu2+ and Eu3+ emissions was reproducible, and, with increasing content of Eu, the relative intensity of the red component from Eu3+ became systematically stronger. The Eu2+ luminescence in Ca3Y2Si3O12 was characterized by an extraordinary large Stokes shift of ∼8960 cm–1 and most probably had an anomalous character with a defect, presumably O-vacancy located in the vicinity of Eu2+, being involved in the emission generation. Excitation into the VUV-UV region with synchrotron radiation revealed that at 10 K, despite Eu3+ and Eu2+ ions, two kinds of intrinsic emissions, peaking around 340 and 420–440 nm, contributed to the luminescence of Ca3Y2Si3O12:Eu. Luminescence measurements in the range of 293–573 K and decay kinetics of Eu3+ and Eu2+ emissions revealed that the continuously decreasing fraction of Eu2+ ions contributed to the emission with increasing temperature, yet the thermal quenching of emission monitored by changes in its decay time could merely be seen above 500 K. The unusual temperature behavior of Eu2+ luminescence in Ca3Y2Si3O12:Eu2+,Eu3+ was assigned to the instability of exciton-like state diffused over [Eu2+-Ovac] defect cluster involved in the luminescence of Eu2+. Although the performance of the phosphor was not optimized, 40–44% of the quantum efficiency of the overall luminescence upon near-UV excitation was measured, proving its high potential.