Site Selective Excitation and Upconversion in Er3+:KLiYF5

KLiYF5 is a promising new laser host crystal. Nd3+:KLiYF5 forms the basis of a low threshold infrared laser1, and has also been characterized for its potential as an upconversion laser.2 We have measured the low temperature excitation and emission spectra of a single crystal of 1% Er3+: KLiYF5. The rare earth ions reside in two similar but optically separable sites. The similarity of the centers is obvious because of one to one correlation in the number of spectral lines, similar strengths and polarisations of transitions, and very small shifts in energy (typically less than 10cm1) between corresponding levels. Selective excitation and emission experiments have been performed using a pulsed tunable dye laser in the wavelength range 450nm to 700nm. With a combination of excitation and emission experiments, positions of all levels below 25,000cm-1 have been determined. Lifetimes relevant to the upconversion work have been measured.