Multilayer electroluminescent devices with a system in which red-emitting quantum dots doped PVK serves as the active layer is fabricated through non-treatment process, the device structure being ITO/PVK:QDs/Alq3/Al. Measuring the emission spectra and electrical characteristics of the devices we study the effect of different QDs doping concentration (mass fraction), and propose some possible solutions to optimize the PVK:QDs system after taking pure QDs for comparison. Experimental results show that changing QDs doping concentration would bring significant impact on the electroluminescence (EL) spectra, current density, brightness, and the stability of devices. When QDs doping concentration is low, we will mainly see the light of Alq3; when QDs doping concentration is 20%, saturated pure red light emission is observed and it is brighter than other devices. However, when the doping concentration is high, a slight red shift occurs in the EL spectra, and the performance of the device gets worse. With a suitable doping concentration, the PVK:QDs may increase the stability of devices.