Combustion Synthesis and Optical Property Tuning of Cerium Activated Gadolinium Aluminum Garnet (GAG) Phosphor Powders

Cerium-doped gadolinium aluminum garnet (GAG:Ce) can be used to improve the efficiency of white-light LEDs (light emitting diodes). The Rogers group has gained expertise in combustion synthesis of yttrium aluminum garnet doped with Ce and/or Eu, however the process procedure does not produce good quality, pure phase GAG.  This project focused on developing a gel-combustion synthesis of GAG:Ce.  Photoluminescence (PL) spectroscopy, powder x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) were used to characterize the effects of processing conditions on the resulting materials’ properties. Fuel type, combustion temperature, annealing temperature and annealing time were investigated.  XRD showed that nearly pure phase GAG was formed by using citric acid as the fuel, a combustion temperature of 500°C, and a 4.5 hour, 1100 °C anneal.  The trends observed in our results are consistent with phase diagrams that indicate pure-phase GAG should be formed at 1200 °C and above. Material combusted at 400 °C and annealed for 14 hours at 1100 °C had the most intense PL emission but did not contain the most garnet phase of the materials produced. This observation indicates PL emission intensity depends on factors in addition to crystal phase. We investigated the effects of substituting host ions on GAG PL intensity. Yttrium was substituted for gadolinium, and gallium was substituted for aluminum in the GAG lattice. XRD and XPS analyses were used to interpret the trends in PL emission of these host-doped materials.