The Effect of Li on the Spectrum of Er³⁺ in Li- and Er-Codoped ZnO Nanocrystals

Abstract

Infrared-to-visible upconversion emission intensities are investigated in Li+ and Er3+ codoped ZnO nanocrystals. Li+ ions doped in ZnO/Er3+ nanocrystals can greatly enhance the upconversion emission intensity of Er3+ ions. The extended X-ray absorption fine structure spectroscopy data show that both the Er−O bond length and coordination number of the Er−Er bond have been altered by introducing Li+ ions in the ZnO/Er3+ nanocrystals. The variation of Er−O bond length leads to the change in the local asymmetry around Er3+ ions. Meanwhile, the greater coordination number of the Er−Er bond causes stronger interaction between neighboring Er3+ ions and, hence, strengthens the reaction Er3+ (4F7/2) + Er3+ (4I11/2) → 2Er3+ (4F9/2). In this process, the 4F9/2 state is a metastable state that could be excited to the 2H9/2 state by absorbing one photon at high excitation power. Li+ ions also can reduce the OH groups in specimen, which is the other reason for enhancing the upconversion emission intensities.

Enhance upconversion photoluminescence intensity by doping Li+ in Ho3+ and Yb3+ codoped Y2O3 nanocrystals

“…We find that the UC-PL intensity of Er 3+ could be greatly enhanced by doping Li + in Y 2 O 3 :Er 3+ and ZnO:Er 3+ [12,13]. And we further study the effect of Li + on the spectrum of Er 3+ in ZnO:Er 3+ /Li + nanocrystals [14]. The causes for the enhancement are attributed to the modification of the local symmetry around the Er 3+ ion and the reducing OH groups.…”

Enhancement of upconversion emission in Y3Al5O12:Er3+ induced by Li+ doping at interstitial sites

“…But, the forbiddance can be partially broken when the rare-earth ion situates at low symmetry sites [7][8][9][10]. Hence, the modification of rare-earth ions' local environment can be a promising route to enhance their luminescence intensity.…”

Upconversion luminescence enhancement and temperature sensing behavior of F− co-doped Ba3Lu4O9:Er3+/Yb3+ phosphors

“…Therefore, enhancing the UC luminescence intensity is one of the signicant issues and great challenge for its actual application. Recently, many kinds of techniques were adopted to improve the UC emission intensity, such as changing the crystal phase of host materials, 8,9 adding Nb to reduce phonon energy, 10 incorporating impurities such as Li + , Zn 2+ to modify the local crystal eld around RE 3+ ions, [11][12][13] introducing core-shell structure, 14 and crystal surface coating. 15 It is well-known that the UC emission intensity of RE 3+ doped phosphor is strongly dependent on their intra 4f-4f transition possibility.…”