Abstract
PbWO4: Er3+,Yb3+ nanocrystals (∼100 nm) were prepared by the hydrothermal method at different pH values (pH = 4, 7, and 9). Their structure and luminescence properties under 978-nm laser-diode excitation were studied. The results indicate that the practical ratio of W to Pb in the nanocrystals and the doping concentration of Yb3+ depended strongly on the pH value due to structure change. In upconversion, red (4F9/2→4I15/2) and green (2H11/2,4S3/2→4I15/2) emissions were observed, both of which occurred via a two-photon populating process. Biexponential upconversion dynamics were observed, which was attributed to luminescence centers surrounded by different local environments. The intensity ratio of 2H11/2→4I15/2 to4S3/2→4I15/2 (RHS) was explored to reveal the local thermal effect under the exposure of the laser diode, showing that the temperature at the exposed spot increased linearly with respect to excitation power density and Yb3+ concentration.
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