Upconversion luminescence of Er3+-doped YSZ single crystals

The upconversion luminescence of erbium-doped yttria stabilized zirconia single crystals was studied upon excitation in the near-infrared region inside the I-4(9/2) level. Direct excitation in the visible region was also carried out. A strong green luminescence from the S-4(3/2) level, and a less intense red emission from the F-4(9/2) level, were observed for both visible and upconversion excitations. Absorption measurements and direct site-selective emission measurements revealed the presence of different types of optical Er3+ centers. Pulsed and continuous IR excitation experiments show that different optical centers undergo upconversion processes. Cw infrared excitation, compared with both pulsed infrared excitation and direct visible excitation, seems to be a more sensitive site-selective technique. High power continuous excitation 'saturates' the upconverted emission, while high power pulsed excitation increases the rate of the upconversion luminescence. It is concluded that the upconversion mechanisms are not the same for high power pulsed and continuous excitation. (C) 2001 Elsevier Science B.V. All rights reserved.