%0 Journal Article
%T One-Pot Solvothermal Synthesis of Highly Emissive, Sodium-Codoped, LaF3 and BaLaF5 Core-Shell Upconverting Nanocrystals
%A Joshua T. Stecher
%A Anne B. Rohlfing
%A Michael J. Therien
%J Nanomaterials
%D 2014
%I MDPI AG
%R 10.3390/nano4010069
%X We report a one-pot solvothermal synthesis of sub-10 nm, dominant ultraviolet (UV) emissive upconverting nanocrystals (UCNCs), based on sodium-codoped LaF 3 and BaLaF 5 (0.5%Tm; 20%Yb) and their corresponding core@shell derivatives. Elemental analysis shows a Na-codopant in these crystal systems of ~20% the total cation content; X-ray diffraction (XRD) data indicate a shift in unit cell dimensions consistent with these small codopant ions. Similarly, X-ray photoelectron spectroscopic (XPS) analysis reveals primarily substitution of Na + for La 3+ ions (97% of total Na + codopant) in the crystal system, and interstitial Na + (3% of detected Na +) and La 3+ (3% of detected La 3+) present in (Na)LaF 3 and only direct substitution of Na + for Ba 2+ in Ba(Na)LaF 5. In each case, XPS analysis of La 3d lines show a decrease in binding energy (0.08¨C0.25 eV) indicating a reduction in local crystal field symmetry surrounding rare earth (R.E. 3+) ions, permitting otherwise disallowed R.E. UC transitions to be enhanced. Studies that examine the impact of laser excitation power upon luminescence intensity were conducted over 2.5¨C100 W/cm 2 range to elucidate UC mechanisms that populate dominant UV emitting states. Low power saturation of Tm 3+ 3F 3 and 3H 4 states was observed and noted as a key initial condition for effective population of the 1D 2 and 1I 6 UV emitting states, via Tm-Tm cross-relaxation.
%K near-infrared to ultraviolet upconversion
%K photoluminescence
%K upconversion nanocrystals
%K impurity doping
%K lanthanide
%K LaF3
%K BaLaF5
%K core-shell
%U http://www.mdpi.com/2079-4991/4/1/69