Photoluminescence and chemical properties of ZnS:Mn²⁺ nanocrystal powder synthesized in the AOT reverse micelles modified with lauryl phosphate

A transparent colloidal solution of the ZnS:Mn²⁺ nanocrystal was prepared in hybrid reverse micelles comprising two kinds of surfactants: sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and lauryl phosphate (HLP). Then, the powdered sample was obtained from the colloidal solution by coagulation of these micelles. Modification of HLP surfactant increases the photoluminescence (PL) intensity due to the d-d transition of Mn²⁺ ions for both of the colloidal solution and the powder. FT-IR spectra and energy dispersive X-ray analysis (EDX) data reveal that HLP modifies ZnS:Mn²⁺ nanocrystals more preferentially than AOT. The detailed investigation on chemical interaction between HLP molecules and ZnS nanocrystals with and without Mn²⁺ is performed by solid-state nuclear magnetic resonance (NMR) techniques of ³¹P inversion recovery and ¹H → ³¹P cross-polarization (CP) in a magnetic field of 11.7 T using magic angle spinning (MAS) at a high spinning rate of 19 and 28 kHz, respectively. These NMR results suggest that most of HLP molecules strongly interact with nanocrystals through coordination bonds and/or hydrogen bonds.