Fig. 1

i XRD patterns of the prepared 2%Er³⁺, 20%Yb³⁺-codoped BaYF₅, pH is equal to 9 except (a), whose pH equals 4. (a) 200 °C, 16 h. (b) 200 °C, 12 h. (c) 200 °C, 16 h. (d) 200 °C, 24 h. (e) 180 °C, 16 h. (f) 220 °C, 16 h. The standard XRD pattern of BaYF₅ (JCPDS no.46-0039) and BaF₂ (JCPDS no.85-1342) is also given for comparison. ii EDS of the product corresponding to XRD (d). iii UC emission spectra of the samples synthesized at 200 °C, (a) 12 h, (b) 16 h, (c) 24 h. iv UC emission spectra of the products synthesized for 16 h. (a) 180 °C, pH = 9. (b) 200 °C, pH = 9. (c) 220 °C, pH = 9. (d) 200 °C, pH = 4. v SEM images of the prepared BaYF₅ synthesized under different conditions. (A) 200 °C, 16 h. (B) 220 °C, 16 h. (C) 200 °C, 24 h