Upconversion luminescence modulated by alkali metal (Li, Na, and K) induced crystallization in Er3+/Yb3+ co-doped β-PbF2 oxyfluoride glass ceramics. Issue 4 (20th December 2019) - Guo, Yuao
Abstract : Upconversion luminescence of Er 3+ /Yb 3+ co-doped β-PbF2 oxyfluoride glass ceramics modulated by alkali metals (Li, Na, and K). Abstract : Alkali metal ions (Li +, Na + and K + ) are introduced into oxyfluoride glass ceramics (GCs) by a traditional melt-quenching and thermal treatment method to regulate crystallization behavior and upconversion luminescence (UCL) of β-PbF2 :Er 3+ /Yb 3+ nanocrystals (NCs). The crystallization behavior of β-PbF2 :Er 3+ /Yb 3+ NCs in GCs is characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), EDX analysis, Raman spectroscopy and photoluminescence (PL) spectroscopy with Eu 3+ ions as structural probes. Li +, Na + and K + ions are inserted into a glass matrix to destroy its glass network structure, which results in fluoride crystallization even without thermal treatment. Compared with alkali metal ion-free doped GCs, crystallization behavior and UCL properties of β-PbF2 :Er 3+ /Yb 3+ NCs in Li + doped GCs are almost unchanged because Li + ions are too small to incorporate into the β-PbF2 :Er 3+ /Yb 3+ NCs. Na + and K + ions are believed to enter the β-PbF2 lattice by substituting Pb 2+ ions due to their similar ionic radii. Na + ions as charge compensation ions doped into the β-PbF2 :Er 3+ /Yb 3+ NCs result in sharp lattice shrinkage due to their smaller ionic radius than Pb 2+ ions. β-PbF2 :Er 3+ /Yb 3+ NCs doped with Na + ions become more crowded because of a tight network structure limited by a Si–O layer. The crowded growth of β-PbF2 :Er 3+ /Yb 3+ NCs results in a very small distance between Er 3+ and Yb 3+ ions, which leads to a strong EBT process between Er 3+ and Yb 3+ ions, then a nearly pure red UCL emission (the maximum intensity ratio of red to green (RRG)) was obtained. Meanwhile, K + ions as charge compensation ions doped into the β-PbF2 :Er 3+ /Yb 3+ NCs result in slight lattice expansion of the β-PbF2 :Er 3+ /Yb 3+ NCs due to the larger ionic radius of K + ions than that of Pb 2+ ions. K + ions could act as a self-promoting agent for the enhanced crystallization of the β-PbF2 :Er 3+ /Yb 3+ NCs. UCL intensity of β-PbF2 :Er 3+ /Yb 3+ NCs doped with K + ions increases by about 30 times due to high crystallinity and lattice distortion around Er 3+ ions. The results show that simultaneous co-doping of alkali metal ions (Li +, Na + and K + ) in oxyfluoride GCs is a very effective way to integrate this material for advanced photonic applications.