Effect of Bi3+ addition on the upconversion luminescence properties of NaYbF4:Er

In this study, Bi(3+) incorporation in NaYbF4 :Er lattice and its influence on upconversion luminescence properties have been investigated in detail using techniques such as temperature-dependent luminescence, Fourier transform infrared spectroscopy and X-ray diffraction (XRD). The study was carried out to develop phosphors with improved upconversion luminescence. From photoluminescence and lifetime measurements it is inferred that luminescence intensity from NaYbF4 :Er increases with Bi(3+) addition. The sample containing 50 at.% Bi(3+) ions exhibited optimum upconversion luminescence. Increased distance between Yb(3+) -Yb(3+) and Er(3+) -Er(3+) due to Bi(3+) incorporation into the lattice and associated decrease in the extent of dipolar interaction/self-quenching are responsible for increase in lifetime values and luminescence intensities from Er(3+) ions. Incorporation of Bi(3+) into NaYbF4 :Er lattice reduced self-quenching among Yb(3+) -Yb(3+) ions and this facilitated energy transfer from Yb(3+) to Er(3+) . This situation also explains decrease in the extent of temperature-assisted quenching of emission from thermally coupled (2) H11/2 and (4) S3/2 levels of Er(3+) . Based on Rietveld refinement of XRD patterns it was confirmed that a maximum of 10 at.% of Bi(3+) added was incorporated into the NaYbF4 :Er lattice and the remaining complex co-exists as a BiOF phase. These results are of significant interest in the area of development of phosphors based on Yb(3+) -Er(3+) upconversion luminescence.