Upconverting crystals are being currently actively studied for applications in engineering and biomedicine due to their high infrared-to-visible conversion efficiency. Near-field microscopy is used for the first time to measure the luminescence distribution over the area of β-NaYF4:Yb/Er microcrystals. It is shown that the luminescence intensity generally decreases from the crystal center to its periphery, which may be due to erbium depletion during crystal growth. The obtained information may be useful for improving the growth technology of upconverting crystals and enhancing their luminescence.
Krotova et al. (Mon,) studied this question.