Observation of a red Ce3+ center in SrLu2O4:Ce3+ phosphor and its potential application in temperature sensing

Abstract

In Ce³⁺ activated SrLn₂O₄ type phosphors (Ln = Y, Lu, Sc, etc.) only one Ce³⁺ center was previously reported to show a blue emission band. In this paper, we report the observation of a second Ce³⁺ center in SrLu₂O₄:Ce³⁺. The new center shows a red emission band peaking at 600 nm with an excitation band at 485 nm. We attributed the new center (Ce(II)) to the substitution of the Lu³⁺ site and the original blue center (Ce(I)) to the substitution of the Sr²⁺ site. Spectroscopy studies indicate that Ce(I) centers are preferentially formed at a low doping concentration and the number ratio of Ce(I)/Ce(II) decreases with increasing Ce³⁺ concentration until beyond 0.002. The fluorescence lifetimes of the two centers were measured for various doping concentrations. Energy transfer from Ce(I) to Ce(II) was observed. It was found that the emission intensity of Ce(II) centers reduces much faster than that of Ce(I) with increasing temperature from 83 K up to 350 K, implying their potential application in temperature sensing based on their temperature dependent intensity ratios. A relative sensing sensitivity as high as 2.28% K⁻¹ at 283 K was achieved.