Temperature Dependent Fluorescence of Ce-doped Garnets For Use as Thermographic Phosphors

Four samples of (Y1−xCex)3(Al1−yGay)5O12 (where x=0.01, 0.02 and y=0, 0.5) were synthesized via the simple, efficient combustion synthesis method in order to determine the effect of substituting Ga for Al on the temperature-dependent fluorescent lifetime. X-ray diffraction(XRD) data show that the average crystallite size is 20-30nm and that the gallium-doped samples have longer lattice constants and smaller average crystallite sizes relative to the singledoped samples. Transmission electron images confirms the average crystallite size from XRD data and reveal large agglomerates composed of nanocrystalline particles. Photoluminescence data reveals that the addition of gallium into the YAG:Ce matrix induces a red shift in the absorption spectra and a blue-shift in the emission spectra. The emission spectra of the gallium-doped samples shows an intense broad-band emission centered at approximately 520nm and a low-intensity, broad-band emission centered at 700nm. The laser-induced fluorescent lifetime was determined as a function of temperature over the range of 0-125◦C using red and green emission filters. Increasing the amount of dopant ultimately results in a decrease of the fluorescent lifetime. The quenching temperatures for the Ga-doped samples were lower than the samples without gallium. The lowest quenching temperatures were observed when using the red emission filter. The results of this work show that a simple, inexpensive combustion synthesis reaction is viable method for making highly luminescent, nanocrystalline TGPs. In addition, we have shown that the quenching temperature of YAG:Ce can be altered by substituting ions which alter the location of the charge transfer state and by collecting emission at a longer wavelengths.