Orientation of molecular spins in colloidal quantum dots: toward hybrid spinphotonics – HSP

The HSP-project aims at contributing to the development of new opto-magnetic systems for information treatment or information storage in the frame of spin-photonics. Indeed, we intend to exploit the ultra-fast formation of magnetic polarons reported in Diluted Magnetic Semiconducting (DMS) nanoparticles while improving the efficiency and the versatility of the process. This phenomenon exists in Mn(II)-doped quantum dots but the synthesis of Mn-doped CdSe nanoparticles is hampered because Mn(II) ions are not prompt to intercalate in the hexagonal wu¨rtzite structure of CdSe. To circumvent this issue, we propose to synthesize CdSe nanocrystals (NCs) decorated at their surface by paramagnetic coordination complexes. These hybrid NCs that we call HDMS-NCs, will allow for the formation of magnetic polarons and will therefore present a spontaneous magnetization under irradiation.
For the synthesis of these hybrid systems, we will develop a versatile three-step strategy, which has already been used with success for the synthesis of Mn(DTPA)-CdSe nanosystems. The first step consists of synthesizing the CdSe QDs core by well-know hot-injection procedures. The second step involves ligand exchange at the surface of the QDs to graft short bridging ligands able to further coordinate a complex. Finally the complexes will be linked to the QDs’ surface by a solution route. With this approach we will have access to an easier and versatile synthesis because various metal complexes with various magnetic properties could be grafted at the surface; and this will lead to the tuning of the magneto-optic properties of the hybrid nanoparticles. This strategy will also yield a better ratio Mn/CdSe leading to higher magnetization, the tuning of the magnetic properties depending on the choice of the coordination complexes grafted at the surface of the hybrids. Moreover, the use of organic ligand at the surface of the hybrid particles will be a strong asset for the processing of the particles as thin films in order to integrate these hybrid particles into devices intended to ultra-fast information treatment or storage.
The steady state properties of HDMS-NCs will be studied by photo-SQUID magnetometry and photo-EPR spectroscopy as well as Optically Detected Magnetic Resonance (ODMR). In addition, time-resolved photoluminescence and time-resolved absorption spectroscopies will enable to get a fine understanding of the dynamics and kinetics of the magneto-optical properties of HDMS-NCs.
At last, HDMS-NCs will be integrated on gold and silicon substrates in order to foreshadow future integration in devices.