Spectroscopic Study of Neodymium-Doped Sodium–Yttrium Double Fluoride Nd3+:Na0.4Y0.6F2.2 crystals

Abstract

Nd3+:Na0.4Y0.6F2.2 (Nd3+:NYF) crystals are grown by the Stockbarger–Bridgman method for a stoichiometric mixture prepared by the solid-phase method and containing neodymium up to 20 at. %. The absorption spectrum of Nd3+:NYF crystals exhibits bands located in the emission region of laser diodes. The peak absorption cross section of the 796.8-nm band is σ a = 0.96 × 10–20 cm2 and the bandwidth is Δλ = 17.5 nm. The most intense luminescence band is located at 1.05 μ m and the radiative time of the 4F3/2 level is τ0 = τexp ~ 960 μ s. It is shown that the 2P3/2 and 4D3/2 levels of Nd3+:NYF crystals are also radiative with lifetimes τ exp equal to ~110 and 9.5 μ s, respectively. However, these radiative transitions are partially quenched due to nonradiative relaxation. The intensity parameters Ω t are determined by the Judd–Ofelt method to be Ω2 = 1.18 × 10–20, Ω4 = 1.55 × 10–20, and Ω 6 = 2.85 × 10–20 cm 2. Using these parameters, the probabilities of radiative transitions and branching ratios are calculated, and the probabilities of nonradiative transitions are estimated. A conclusion is made that Nd3+:NYF crystals are promising as active media for diode-pumped tunable lasers, in particular, up-conversion-pumped lasers.