Li+ Co-Doping Effect on the Photoluminescence Time Decay Behavior of Y2O3: Er3+ Films

The incorporation of rare earth ions in metal oxides has received considerable attention for great variety of applications such as, biomedical, optical amplifier, active waveguide, solar cell, etc. In particular, Er³⁺ ion shows interesting characteristic emissions in the 520-580, 640-700, 1520-1580 nm ranges, which are suitable for most of the applications mentioned above. The use of thin film phosphors offers some advantages over bulk powders such as a better thermal stability, better adhesion, and good uniformity coverage of substrate surfaces. However, the main drawback of phosphor films has been their low brightness in comparison with bulk powders. Recently, it has been reported that the incorporation of Li⁺, Na⁺ and K⁺ alkali ions enhances considerably the luminescent efficiency of rare earths. In this work, the effect of Li⁺ co-doping on photoluminescent time decay characteristics of Y₂O₃: Er³⁺ is reported for films deposited by ultrasonic spray pyrolysis at 500°C. The Er³⁺ content was fixed at 1.5 at% while the Li⁺ content in the spraying solution was varied from 1 to 4 at% in relation to Y³⁺. It is observed that the addition of Li⁺ content up to 2 at%, besides resulting in an increase of the luminescence emission intensity, modifies the luminescence time decay behavior as well. In general, the decay profiles under 207 and 414 nm excitation are not fitted to a simple exponential. They seem to be composed by an initial slow decay followed by a faster decay. This behavior is associated with a charge transfer process.  A simple model in which charge transfer from localized centers to the Er³⁺ ions is used to describe the evolution with time of the luminescence emission. The introduction of Li⁺ ions in the Y₂O₃: Er³⁺ seems to have an impact on both the effectiveness of the charge transfer process and on the total number of Er³⁺ ions contributing to the luminescence emission.