On the mechanism of persistent up-conversion luminescence in the ZrO2:Yb3+,Er3+ nanomaterials

• Yb3+,Er3+-doped ZrO2 nanomaterials show red and weak green up-conversion luminescence from Er3+.
• Along with conventional up-conversion, short persistent emission is detected upon NIR excitation.
• Charge compensation creates defects due to rare earths substituting for Zr in the ZrO2 host.
• Thermoluminescence glow curves yield traps with depths matching ambient persistent emission.
• Energy level positions in the band gap of ZrO2 suggest hole trapping near the top of valence band.

The up-converting ZrO2:Yb3+,Er3+ nanomaterials were prepared with the combustion and sol–gel methods. The structure of the materials was cubic except for the minor monoclinic and tetragonal impurities associated with the use of the sol–gel method. The XANES results revealed only the trivalent form for both the Yb and Er dopants. The distance distributions calculated from EXAFS confirm that Er3+ and Yb3+ occupy the ZrIV site in the structure. The nanomaterials show red (650–700 nm) and very weak green (520–560 nm) up-conversion luminescence due to the 4F9/2 → 4I15/2 and (2H11/2,4S3/2) → 4I15/2 transitions of Er3+, respectively. The nanomaterials obtained with the combustion synthesis yield the most intense luminescence though showing significant afterglow, as well. The thermoluminescence measurements revealed the existence of traps with depths between 0.68 and 1.03 eV well matching to room temperature persistent emission. Finally, the mechanism for the persistent up-conversion luminescence was introduced based on the experimental results and discussed.

Figure optionsDownload high-quality image (166 K)Download as PowerPoint slide