Citric acid trisodium salt dihydrate

Rare earth (RE) oxides: Er₂O₃ and Yb₂O₃ (99.99%, Stanford Materials, United States) were dissolved separately in hydrochloric acid, HCl (ultra-pure, Sigma-Aldrich, 37%, Poland) in order to obtain respective rare earth chloride solutions in a concentration of 1 or 0.25 M. Ammonium fluoride, NH₄F (98+%, Sigma-Aldrich, Poland) was used as the source of fluoride ions. Strontium chloride hexahydrate SrCl₂·6H₂O (Sigma-Aldrich, 99+%, Poland), citric acid trisodium salt dihydrate, (Sigma-Aldrich, 97%, Poland) and ammonium citrate tribasic, (Sigma-Aldrich, ≥97%, Poland), phosphate buffered saline (BioShop), poly(ethylene glycol) bis(carboxymethyl) ether (average M_n 250, Sigma-Aldrich, Poland), polyacrylic acid (average M_w 1800, Sigma – Aldrich, Poland) were used as received, without further purification. Deionized water was used for the synthesis.

All chemicals were purchased from commercial suppliers and used without further purification. CTAB (Bioxtra, ≥99.0%), BDAC (cationic detergent), cetyltrimethylammonium chloride, citric acid trisodium salt dihydrate (≥99.5%, BioUltra, for molecular biology) (CTAC, ≥98.0%), hydrogen tetrachloroaurate trihydrate (HAuCl₄·3H₂O) and L-ascorbic Acid (Bioxtra, ≥98.0%) were purchased from Sigma Aldrich. Silver nitrate (AgNO₃, ≥99.8%) and sodium borohydride (NaBH₄, ≥99%) were purchased from Fluka. Hydrochloric acid (HCl, 1 N) was purchased from Fisher scientific. Nanopure water (18.2 MΩ, Barnstead Nanopure, Thermo Scientific, MA, USA) was used in all experiments. The glass vials were purchased from Kimble chase (4 and 20 ml, NJ, USA). All glasswares were cleaned using freshly prepared aqua regia (HCl:HNO₃ in a 3:1 ratio by volume) followed by rinsing with copious amounts of water. RCT Basic (IKA, NC, US) was used for magnetic stirring. Ultraviolet–vis–near-infrared spectra were measured with Synergy H4 (Biotek, VT, USA) and Cary 5000 ultraviolet–vis–near-infrared (Agilent, CA, USA). The formvar/carbon-coated copper grid (Ted Pella, Inc. Redding, CA, USA) and TEM (Tecnai G2 F30 Super Twin microscope, 300 kV and Tecnai G2 Spirit, 200 kV, FEI, OR, USA) were used for the TEM analysis.