Hybridization of CdSe/ZnS Quantum Dots on InGaN/GaN Multiple Quantum Well Light-Emitting Diodes for Pink Light Emission

Pink light emission has been demonstrated from the hybrid CdSe/ZnS quantum dot-InGaN/GaN quantum well light-emitting diodes (LEDs). The QDs in toluene are blended in the resin matrix to become the nanophosphor. For the fabricated hybrid LED, it is found the light output power is greatly reduced due to the poor quantum yield (QY) of QDs (<50%). Besides, the comparison of the electroluminescence (EL) spectra of the InGaN blue LED and the hybrid pink LED exhibit over 90% of the blue light centered at 448 nm has been down-converted to the red light at 636 nm. Consequently, purplish pink light with CIE-1931 chromaticity coordinates of (0.374, 0.147) is obtained. Also observed is the significant blue-shift of luminescence peak from QD-resin composite with respect to the photoluminescence peak from QD-toluene solution, which is due to the less attack of reabsorption of photon energies from smaller to larger QDs rather than the Forster energy transfer. The current-dependent and temperature-dependent EL spectra are also characterized to evaluate the thermal stability of our hybrid LED. In this demonstration, CdSe/ZnS QDs with different sizes/colors can be used as nanophosphors to fabricate color-converted LEDs. Nevertheless, QDs with higher QYs or more efficient device packagings should be adopted to improve the device efficiency.