 
 <prompt> Flourescence dey come out from where? Given di last question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: The arrangement of QD-LEDs wey dem use for the electrical-excitation scheme dey similar to the basic design of OLEDs. One layer of quantum dots dey sandwiched between layers of electron-transporting and hole-transporting materials. When electric field dey applied, electrons and holes dey move enter the quantum dot layer and come together to form an exciton wey go excite a QD. People dey commonly study this arrangement for quantum dot display. The ability to change emission wavelengths and the small bandwidth dey useful as excitation sources for fluorescence imaging. Dem don demonstrate the use of Fluorescence near-field scanning optical microscopy (NSOM) wey dey use an integrated QD-LED. 