  We discuss photo-luminescence characteristics of CdSe core/shell quantum dots
at cryogenic temperatures using a hybrid system of a single quantum dot and an
optical nanofiber. The key point is to control the emission species of quantum
dot to charged excitons, known as trions, which have superior characteristics
to neutral excitons. We investigate the photocharging behavior for the quantum
dots by varying the wavelength and intensity of irradiating laser light, and
establish a method to create a permanently charged situation which lasts as
long as the cryogenic temperature is maintained. The present photocharging
method may open a new route to applying the CdSe quantum dots in quantum
photonics, and the hybrid system of photocharged quantum-dot and optical
nanofiber may readily be applicable to a fiber-in-line single-photon generator.
