Intense green upconversion emission by photon avalanche process from Er3+/Yb3+ co-doped NaBi(WO4)2 phosphor

Abstract

The Er3+/Yb3+ co-doped NaBi(WO4)2 (NBW) phosphor has been synthesized by conventional solid state reaction technique. The XRD analysis confirms the tetragonal crystal structure of NaBi(WO4)2. An intense green upconversion (UC) emission by photon avalanche (PA) process has been observed under excitation with 980 nm laser at room temperature. The observed green emission is due to 2H11/2, 4S3/2→4I15/2 (523, 548 nm) transitions of Er3+ ion. The green emission dominate because the intensities of other peaks are very small. The average number of photons involved in the UC process is 8.4 for 523 nm emission, the rise time of 2H11/2 level decreases with increasing the laser power and the power versus emission intensity plot is concave type. These are the characteristics of PA process. The PA process has been explained by looping energy transfer mechanism. In the present case, the PA appeared at very low power (<30 mW). This material may be applicable in intense green emission, finger printing, green component of white light and other optical devices.