Upconversion pumping with yellow cw and pulsed dye lasers was used to
produce uv and blue light arising from decxcitation of the 4D3/2 and P
-2(3/2) states of Nd3+ ions in BaY2F8:Nd3+. Upconversion excitation oc
curs via sequential two-photon absorption, which was probed by the ant
i-Stokes emission dynamics and by a two-color laser experiment. An ana
lysis of the steady-state populations as a function of pumping rates R
1 and R2 for the two-step excitation is developed. When the excitation
frequency is resonant with the F-4(3/2)=>4D3/2 excited-state absorpti
on transition, the power dependence of the anti-Stokes fluorescence in
tensity, plotted on a logarithmic scale, shows a straight line with a
slope of 1.8. This behavior is explained quite well by the model for a
mean-excitation-power regime where the second step is 4 orders of mag
nitude more efficient than the ground-state absorption.