Core-shell structure ZnS:Tb/CdS nanocrystals(NCs) with sizes of about 4 nm were synthesized via reverse microemulsion technique. The structures

shapes and characteristic optical properties of ZnS:Tb/CdS NCs were characterized by means of X-ray powder diffraction(XRD)

transmission electron microscopy(TEM) and F-4500 Fluorescence spectrometer. The XRD pattern of ZnS:Tb/CdS NCs was shown that the crystals (exhibit) zinc-blend crystal structure. The three diffraction peaks are corresponding to (111)

(220)

and (311) planes of the cubic crystalline ZnS

respectively. Due to the size effect

the XRD peaks were broadened and their widths become larger as the crystals become smaller. From the XRD analysis

no characteristic peaks of impurity phases were observed. The average sizes of ZnS:Tb/CdS NCs were calculated from the Debye-Scherrer equation to be around 3 nm. From typical TEM image

it is noticed that the average size of the ZnS:Tb/CdS NCs is about 4 nm. So the thickness of CdS shell is evaluated to be about 0.5 nm. The PL spectra of ZnS:Tb/CdS excited by 379 nm are composed of three peaks located at 489

543

and 583 nm

which is assigned respectively to

5

D

4

7

F

6

5

D

4

7

F

5

and

5

D

4

7

F

4

electron transitions of Tb

3+

ions. An electroluminescent (EL) device having a hybrid organic/inorganic multilayer structure of ITO/ poly(3

4-ethylene dioxythiophene):poly (styrene sulfonate)(PEDOTPSS)(70 nm)/poly(vinylcobarzale)(PVK)(100 nm)/ZnS:Tb/CdS NCs (120 nm)/2

9-dimethyl -4

7-diphenyl-1

10-phenanthroline (BCP)(30 nm)/LiF (1.0 nm)/Al (100 nm) was fabricated. The two peaks located at 546 nm (

5

D

4

7

F

5

) and 577 nm (

5

D

4

7

F

4

) of the Tb

3+

center were observed when the EL device was driven at applied bias of 13 V. It is also noticed that EL emission from PVK in the device was not observed

indicating that the electron-hole would be recombined in ZnS:Tb/CdS NC layer. The maximum luminance of 19 cd/m

2

was obtained under the applied bias of 25 V.