Fig. 4

i XRD patterns of the prepared 2%Er³⁺, 20%Yb³⁺-codoped BaYF₅ synthesized at 200 °C for 24 h; 5% PEI was added for conducting convenient comparison. (a) and (b) fluoride source was NH₄F and NaF, respectively. The standard XRD pattern of BaYF₅ (JCPDS no.46-0039) is also given for conducting the comparison. ii UC emission spectra of samples. (a) NaBF₄. (b) NH₄F. (c) NaF. iii SEM images of the products (A) NH₄F. (B) NaF