Reinterpretation of the red emission pathway in β-NaYF4:Yb3+, Er3+

Abstract

The β-NaYF4:Yb3+, Er3+ phosphor is well known as one of the high-efficiency upconversion (UC) phosphors. Of the three main emission bands (blue, green and red), the red emission belongs to the “optical window” that can penetrate the biological tissues. For this reason, this phosphor has been received much attention as a luminescent probe for biomedical imaging. This study interpreted the red emission mechanism by energy back transfer (EBT) process by analyzing both the photoluminescence and upconversion photoluminescence properties. Herein, the another pathway of red emission in β-NaYF4:Yb3+, Er3+ phosphor was demonstrated, which belongs to two EBT processes such as 4S3/2→4I13/2 (Er3+):2F7/2→2F5/2 (Yb3+) and 4G11/2→4F9/2 (Er3+):2F7/2→2F5/2 (Yb3+). Since two EBT routes play a key role for generating the red emission, the currently accepted UC mechanism for this phosphor should be modified accordingly.