1. Multibubble sonoluminescence and sonochemistry of f-transition elements Pflieger R., 1 Virot M., 1 Chave T., 1 Schneider J., 2 Nikitenko S.I., 1 1 ICSM, Marcoule, France, 2 MPI, Potsdam, Germany Institute for Separation Chemistry of Marcoule (ICSM), Laboratory of Sonochemistry in Complex Fluids (www.icsm.fr) August 13-16, 2012, Singapore

2. Fluorescence of uranyl ions Uranyl ion UO 2 2+ is a major chemical form of uranium in aqueous solutions Absorption and emission spectra of UO 2 2+ in 0.1M HClO 4 at 25°C (used in analysis) Why U and lanthanides (Tb)?  U is a principal element of nuclear industry  Ln are the important fission products and also they are widely used in industry (catalysis, optics, medical diagnostics, etc.)

3. 3 Multifrequency reactor for MBSL and sonochemistry

4. 4 In HClO 4 UO 2 2+ exhibits extremely weak MBSL MBSL of 0.1M UO 2 2+ in HClO 4 and in H 3 PO at 203 kHz, 10°C, Ar. The inset shows the emission spectrum of 0.2M UO 2 2+ in 0.2 M HClO 4 after photoexcitation at λ = 427 nm. In H 3 PO 4 MBSL of UO 2 2+ is much stronger than that in HClO 4 Strong effect of acid

5. 5 UO 2 2+ SL intensity is strongly influenced by the ultrasonic frequency The strongest intensity of UO 2 2+ SL is observed at 203 kHz ultrasound exhibiting the highest total SL (0.5M H 3 PO 4, Ar)

6. 6 Ultrabright SL of UO 2 2+ in H 3 PO 4 can be seen by the unaided eye! 30 sec

7. 7 The difference between HClO 4 and H 3 PO 4 is attributed to UO 2 2+ quenching Intramolecular quenching with coordinated water: (UO 2 2+ )* + H 2 O → UO 2 + + H + + OH Intermolecular quenching : (UO 2 2+ )* + H 2 O 2 → UO 2 + + H + + HO 2 UO 2 + + OH (HO 2, H 2 O 2 ) → UO 2 2+ Quenching of UO 2 2+ MBSL with 110 -2 M H 2 O 2. 203 kHz, 86 W, 7.210 -3 M UO 2 2+ 0.5 M H 3 PO 4, 10°C, Ar. Stable phosphate complexes UO 2 H x (PO 4 ) n +(2-3n+x) strongly decrease both intra- and intermolecular quenching

8. 8 Effect of UO 2 2+ concentration – an effective tool to elucidate the mechanism of excitation SL photons are totally absorbed by UO 2 2+ (>10 -4 M) Sonophotoluminescence In diluted solutions Contribution of collisional mechanism in concentrated solutions

9. 9 MBSL of Tb(III) in aqueous solutions There is no SL of Tb(III) in diluted (<0.05 M) solutions Tb(III) absorption MBSL spectra of 0.1M TbCl 3 in water (11°C, Ar) Tb(III) emission ________________________ f, kHz P ac, W QY, a.u. ________________________ 20 24 0.40 203 47 0.17 607 41 0.10 PL 0.08 ________________________ In solutions Tb(III) is excited mostly via collisional mechanism Collisional excitation is stronger at low-frequency?

10. 10 MBSL of Tb(III) at the extended solid-liquid interface (Ce 0.9 Tb 0.1 )PO 4 sintered pellet, water, 20 kHz, Ar, 10°C Tb(III) at the interface is excited via sonophotoluminescence mechanism Pellet

11. 11 CONCLUSIONS  MBSL of UO 2 2+ is the first observation of SL for radioactive elements  MBSL of UO 2 2+ and Tb(III) is extremely sensitive to ultrasonic frequency and to the presence of complexing reagents.  Intramolecular and intermolecular quenching strongly influence the intensity of UO 2 2+ and Tb(III) MBSL  The mechanism of UO 2 2+ MBSL seems to vary with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation would add its contribution at higher UO 2 2+ concentration  MBSL of Tb(III) in solutions is triggered mostly by collisional mechanism and by sonophotoluminescence at the extended solid/liquid interface ============================== This work was supported by French ANR program (ANR-10-BLAN-0810) NEQSON

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