EXCITED-STATE ABSORPTION IN BAY2F8-ND3+

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 occurs via sequential two-photon absorption, which was probed by the anti-Stokes emission dynamics and by a two-color laser experiment. An analysis of the steady-state populations as a function of pumping rates R1 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 absorption transition, the power dependence of the anti-Stokes fluorescence intensity, 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 magnitude more efficient than the ground-state absorption.