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Quenching green and enhancing red upconversion emissions of Er3+ by reducing tetragonality in Yb3+ co-doped ferroelectrics

Tung-Ching Huang ,  Wen-Feng Hsieh 

Department of Photonics, Institute of Electro-Optical Engineering, National Chiao Tung Univ, Hsinchu 30050, Taiwan

Abstract

As increasing Yb3+ co-doped concentrations in 6 mol% Er3+ doped PbTiO3, BaTiO3, and SrTiO3 polycrystalline powder samples, we have observed the room-temperature green upconversion (UC) emission at 550 nm being quenched by the simultaneously enhanced red UC emission at 660 nm under the 980-nm laser excitation. For codoping Yb3+ ions up to 6 mol% in PbTiO3 and only Er3+ doped PbTiO3 samples, which still possess relatively large tetragonality, the green UC emission is still much stronger than red one. In these cases, both the UC emissions are dominated by the two-photon process. But, as further increasing the Yb3+ ion concentration, the crystal structures tend to become cubic phase with enhancing red UC emission and almost diminishing in green emission. Since the pure BaTiO3 crystal exhibits weaker tetragonality than PbTiO3, the stronger red emission and weaker green one were expected at the lower codoped Yb3+ concentration in BaTiO3 system than in PbTiO3 one.  The observed quench of green radiation accompanied with enhancement of red radiation should be due to the efficient energy back-transfer (EBT) process as reported by Chen, et al. by raising Yb3+ concentration [1]. The efficient EBT process requires not only level match of 4S3/24I13/2 in Er3+ and 2F7/22F5/2 in Yb3+ but also resonant match of the laser photon energy with the transitions of 4I15/24I11/2 and 4I13/24F9/2 in Er3+ as well as 2F7/22F5/2 in Yb3+. As a result, declining tetragonality results in the centrosymmetric crystal field for high Yb3+-ion concentration to achieve the level matches that is difficult to be fulfilled with asymmetric crystal field in ferroelectric phase.

[1] G. Chen, G. Somesfalean, Y. Liu, Z. Zhang, Q. Sun, and F. Wang, Phys. Rev. B 75, 195204 (2007).

 

 

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium I, by Tung-Ching Huang
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-08 07:24
Revised:   2009-06-07 00:48