Abstract
Yellow and green upconversion fluorescence is observed at room temperature in Nd:YLiF4 by pumping with a high power diode laser around 795 nm (12.6 × 103 cm-1). The upconversion fluorescence was found to be strongest with the pump light polarized parallel to the crystallographic a-axis and was found to be weaker than the 4F3/2 → 4I11/2 near infrared (NIR) fluorescence by about five orders of magnitude. At room temperature, Nd:YLiF4 absorbs strongly between 780 nm and 815 nm because of the 4I9/2 → 4F5/2 and 4I9/2 → 4F3/2 transitions. The 4F5/2 level relaxes non- radiatively to the metastable 4F3/2 level, which is in turn responsible for the NIR fluorescence transitions occurring between 9.2 x 103 and 11.6 x 103 cm–1. The green upconversion emission lies between 18.5 × 103 and 19.3 × 103 cm–1, and the yellow upconversion emission lies between 16.7 × 103 and 17.4 × 103 cm-1. Considerable structure is visible in the spectrum. A possible route to the observed upconversion is absorption of a second laser photon from the 4F3/2 metastable level into the 2D(1)5/2 and/ or 2P1/2 levels. We will present power dependent and time resolved studies of these fluorescence bands and discuss the dynamics of the upconversion process.
© 1992 Optical Society of America
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