Infrared-laser-induced upconversion from Nd3+: LaF3 heteroepitaxial layerson CaF2(111) substrates by molecular beam epitaxy

This paper reports a systematic analysis on the upconversion fluorescence f rom a Nd3+-doped LaF3 planar waveguide grown on (111) oriented CaF2 substra tes by molecular beam epitaxy. A spectroscopic study of upconversion emissi on has been carried out at low temperature. Upon infrared excitation into t he H-2(9/2), F-4(5/2), or F-4(3/2) multiplets of Nd3+, strong uv upconversi on emissions originating from D-4(3/2) to I-4(J) (J = 9/2, 11/2, and 13/2) transitions by a three-photon process have been observed. In addition, othe r upconversion emissions in the green and orange regions due to two-photon processes were also obtained and attributed to the (4)G(7/2) -->I-4(9/2), ( 2)G(7/2) + (4)G(5/2) --> I-4(9/2), and (4)G(7/2) --> I-4(11/2) transitions, respectively. In accordance with our experimental results, two kinds of en ergy-transfer processes are proposed as upconversion mechanisms responsible for the different emissions, and which are supported by a rate-equation an alysis. The green and orange upconversions originate from an energy-transfe r process involving two Nd3+ ions excited in the F-4(3/2) state. For the th ree-photon upconversion, two successive energy cross-relaxation are suggest ed to populate the D-4(3/2) level. The concentration dependence study has s hown that the optimum concentration for a Nd3+ dopant is about 1 at. % for all the upconversion emissions. Owing to a guided configuration, upconversi on emissions that are hardly detectable in a nonguided configuration at tem perature higher than 100 K have now been recorded at room temperature.