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One-Pot Solvothermal Synthesis of Highly Emissive, Sodium-Codoped, LaF 3 and BaLaF 5 Core-Shell Upconverting Nanocrystals

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ABSTRACT

We report a one-pot solvothermal synthesis of sub-10 nm, dominant ultraviolet (UV) emissive upconverting nanocrystals (UCNCs), based on sodium-codoped LaF3 and BaLaF5 (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 La3+ ions (97% of total Na+ codopant) in the crystal system, and interstitial Na+ (3% of detected Na+) and La3+ (3% of detected La3+) present in (Na)LaF3 and only direct substitution of Na+ for Ba2+ in Ba(Na)LaF5. In each case, XPS analysis of La 3d lines show a decrease in binding energy (0.08–0.25 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 2.5–100 W/cm2 range to elucidate UC mechanisms that populate dominant UV emitting states. Low power saturation of Tm3+3F3 and 3H4 states was observed and noted as a key initial condition for effective population of the 1D2 and 1I6 UV emitting states, via Tm-Tm cross-relaxation.

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XPS survey scans of (a1) (Na)LaF3 (pale Blue); (a2) LaF3 (pale Green); (a3) Ba(Na)LaF5 (Blue); and (a4) BaLaF5 (Green) indicating the presence and absence of Na-codopant; normalized XPS La 3d spectral region (b1) (Na)LaF3 (pale Blue); (b2) LaF3 (pale Green); (b3) Ba(Na)LaF5 (Blue); and (b4) BaLaF5 (Green) indicating a shift in binding energy in La 3d5/2 core orbital upon Na+ inclusion.
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nanomaterials-04-00069-f004: XPS survey scans of (a1) (Na)LaF3 (pale Blue); (a2) LaF3 (pale Green); (a3) Ba(Na)LaF5 (Blue); and (a4) BaLaF5 (Green) indicating the presence and absence of Na-codopant; normalized XPS La 3d spectral region (b1) (Na)LaF3 (pale Blue); (b2) LaF3 (pale Green); (b3) Ba(Na)LaF5 (Blue); and (b4) BaLaF5 (Green) indicating a shift in binding energy in La 3d5/2 core orbital upon Na+ inclusion.

Mentions: XPS characterization of Na-codoped LaF3 and BaLaF5 UCNCs, compared to their undoped controls (Figure 4), reveals insights into the surface composition and local crystal field environments of the host matrices. XPS analysis and Gaussian deconvolution of the of Na 1s and La 3d orbital spectra in (Na)LaF3 show a low energy component indicative of interstitial ion insertion into the crystal structure, that is clearly absent in the undoped LaF3 control (Table 2; Figure S3) [42,44]. The presence of this low energy shoulder in both Na 1s and La 3d orbital XPS spectral regions suggests that Na+ inclusion contributes to La3+ substitution, as evidenced by the presence of interstitial La3+ components. The Na 1s line also displays a low binding energy, interstitial component, though less in contribution (2.65%) in total Na+ incorporation versus La3+ substitution (~97%). Analysis and deconvolution of the Na 1s, La 3d, and Ba 3d orbital lines of Ba(Na)LaF5 display a low energy spectral shoulder exhibited in the Ba 3d orbital alone, indicating direct substitution of Na+ for Ba2+ and interstitial Ba2+ inclusion, with no observed La3+ substitution (Table 2).


One-Pot Solvothermal Synthesis of Highly Emissive, Sodium-Codoped, LaF 3 and BaLaF 5 Core-Shell Upconverting Nanocrystals
XPS survey scans of (a1) (Na)LaF3 (pale Blue); (a2) LaF3 (pale Green); (a3) Ba(Na)LaF5 (Blue); and (a4) BaLaF5 (Green) indicating the presence and absence of Na-codopant; normalized XPS La 3d spectral region (b1) (Na)LaF3 (pale Blue); (b2) LaF3 (pale Green); (b3) Ba(Na)LaF5 (Blue); and (b4) BaLaF5 (Green) indicating a shift in binding energy in La 3d5/2 core orbital upon Na+ inclusion.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5304608&req=5

nanomaterials-04-00069-f004: XPS survey scans of (a1) (Na)LaF3 (pale Blue); (a2) LaF3 (pale Green); (a3) Ba(Na)LaF5 (Blue); and (a4) BaLaF5 (Green) indicating the presence and absence of Na-codopant; normalized XPS La 3d spectral region (b1) (Na)LaF3 (pale Blue); (b2) LaF3 (pale Green); (b3) Ba(Na)LaF5 (Blue); and (b4) BaLaF5 (Green) indicating a shift in binding energy in La 3d5/2 core orbital upon Na+ inclusion.
Mentions: XPS characterization of Na-codoped LaF3 and BaLaF5 UCNCs, compared to their undoped controls (Figure 4), reveals insights into the surface composition and local crystal field environments of the host matrices. XPS analysis and Gaussian deconvolution of the of Na 1s and La 3d orbital spectra in (Na)LaF3 show a low energy component indicative of interstitial ion insertion into the crystal structure, that is clearly absent in the undoped LaF3 control (Table 2; Figure S3) [42,44]. The presence of this low energy shoulder in both Na 1s and La 3d orbital XPS spectral regions suggests that Na+ inclusion contributes to La3+ substitution, as evidenced by the presence of interstitial La3+ components. The Na 1s line also displays a low binding energy, interstitial component, though less in contribution (2.65%) in total Na+ incorporation versus La3+ substitution (~97%). Analysis and deconvolution of the Na 1s, La 3d, and Ba 3d orbital lines of Ba(Na)LaF5 display a low energy spectral shoulder exhibited in the Ba 3d orbital alone, indicating direct substitution of Na+ for Ba2+ and interstitial Ba2+ inclusion, with no observed La3+ substitution (Table 2).

View Article: PubMed Central - PubMed

ABSTRACT

We report a one-pot solvothermal synthesis of sub-10 nm, dominant ultraviolet (UV) emissive upconverting nanocrystals (UCNCs), based on sodium-codoped LaF3 and BaLaF5 (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 La3+ ions (97% of total Na+ codopant) in the crystal system, and interstitial Na+ (3% of detected Na+) and La3+ (3% of detected La3+) present in (Na)LaF3 and only direct substitution of Na+ for Ba2+ in Ba(Na)LaF5. In each case, XPS analysis of La 3d lines show a decrease in binding energy (0.08–0.25 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 2.5–100 W/cm2 range to elucidate UC mechanisms that populate dominant UV emitting states. Low power saturation of Tm3+3F3 and 3H4 states was observed and noted as a key initial condition for effective population of the 1D2 and 1I6 UV emitting states, via Tm-Tm cross-relaxation.

No MeSH data available.


Related in: MedlinePlus