Quantum Dots: Next Generation of Electronic Phosphors

Current CRT phosphors rely upon 3-12 micron sized semiconductor grains to convert the electron beam emitted by the cathode into light. These phosphors suffer from low conversion efficiencies (25%), and efforts to improve these systems over the past few decades by altering the stoichiometry have resulted in only minor improvements. Quantum Dot Phosphors(TM) (QDP(TM)) of doped and undoped II-VI semiconductor compounds have the potential of becoming the next generation of phosphor materials, clearing the way for larger, brighter screens with higher spatial resolution. Surface passivated, direct band gap emission QDP(TM) differ from bulk grains in that their small dimensions (diam. of 3 nm) result in a highly localized electron hole pair. With the defect surface states of the nanocrystal passivated, the probability of the localized electron hole pair recombining radiatively is greatly enhanced. The quantum dots, which are more than 1000 times smaller than standard phosphor grains, provide better spatial resolution. In addition, the doped nanocrystals can result in an increased number density of active centers, which is likely to yield higher saturation values under high current density excitation. The goal of the Phase I effort is to develop direct band gap semiconducting quantum dots of CdS along with doped ZnS dots with activator ions including Ag+ and a host of transition metal ions. We will synthesize the quantum dots with proprietary wet chemistry methods and evaluate the electrical and optical properties with a phosphor evaluation CRT system, donated by Sony Corporation.