Luminescence and energy transfer mechanism in Eu3+/Tb3+-co-doped ZrO2 nanocrystal rods

Nanocrystal rods of Eu3+/Tb3+-co-doped ZrO2 were synthesized using a simple chemical precipitation technique. Both ions were successfully doped into the Zr4+ ion site in a mixed structure containing both monoclinic and tetragonal phases. The Eu3+ or Tb3+ singly doped zirconia produced red and green luminescence which are characteristics of Eu3+ and Tb3+ ions, respectively. The co-doped zirconia samples produced blue emission from defect states transitions in the host ZrO2, red and green luminescence from dopant ions giving cool to warm white light emissions. The phosphors were efficiently excited by ultraviolet and near-ultraviolet/blue radiations giving white and red light, respectively. The decay lifetime was found to increase with increasing donor ion concentration contrary to conventional observations reported by previous researchers. Weak quadrupole–quatdrupole multipolar process was responsible for energy transfer from Tb3+ (donor) ion to Eu3+ ion. No energy back-transfer from Eu3+ to Tb3+ ion was observed from the excitation spectra. Temperature-dependent photoluminescence shows the presence of defects at low temperature, but these defects vanished at room temperature and beyond. The Eu3+/Tb3+-co-doped ZrO2 nanocrystal rod is a potential phosphor for white light application using UV as an excitation source. Thermoluminescence measurements show that the inclusion of Tb3+ ion increases trap depths in the host zirconia.