We report on the light-emitting diode (LED) characteristics of core-shell CdSe/ZnS nanocrystal quantum dots (QDs) embedded in $TiO_2$thin films on a Si substrate. A simple p-n junction could be formed when nanocrystal QDs on a p-type Si substrate were embedded in ${sim}5;nm$ thick $TiO_2$ thin film, which is inherently an n-type semiconductor. The $TiO_2$ thin film was deposited over QDs at $200^{circ}C$ using plasma-enhanced metallorganic chemical vapor deposition. The LED structure of $TiO_2$/QDs/Si showed typical p-n diode currentvoltage and electroluminescence characteristics. The colloidal core-shell CdSe/ZnS QDs were synthesized via pyrolysis in the range of $220-280^{circ}C$. Pyrolysis conditions were optimized through systematic studies as functions of synthesis temperature, reaction time, and surfactant amount.