Photoluminescence and structure evolution of laser synthesized ZrO2:Eu3+ nanopowders depending on the dopant concentration

Abstract

Nanosized zirconia doped with europium (ZrO2:xEu3+, x = 0.07–9.95 wt%) and represented by weakly agglomerated spherical particles with the size of 9.7 ± 4.3 nm was synthesized by laser vaporization in an argon atmosphere using a cw CO2 laser. The specific surface area of the obtained nanoparticles is 92 ± 4 m2/g. The XRD study with Rietveld refinement revealed that the phase composition of the samples is represented predominantly by the tetragonal phase with a small content of monoclinic phase. At the concentrations above 4.57 wt%, stabilization of the cubic phase also occurs. The dependence of the PL intensity, PL lifetime, absolute quantum yield, and color coordinates of ZrO2:Eu3+ on the Eu concentration was studied. It was shown that the maximum PL intensity is observed at the concentration of 8.39 wt%. The Eu3+ lifetime decreases from 5.60 to 3.21 ms with a growth of the Eu content. Aging of the samples due to the adsorption of OH groups was revealed. The absolute quantum yield QY was measured for the 575–725 nm region corresponding to the luminescence of europium, and for the 410–725 nm region, which also includes the emission of oxygen vacancies. The QY was found to increase with the growth of Eu concentration, reaching the highest values for ZrO2:8.39Eu3+; it is equal to 1.6 and 17.6% for 575–725 and 410–725 nm regions, respectively. It was shown that variation of the Eu3+ concentration and excitation wavelength makes it possible to obtain color coordinates with red and close to white light. Along with the high QY for the region of 410–725 nm, this indicates that it is more promising to use ZrO2:Eu3+ as the white phosphor rather than the red one.