Spectroscopic study of neodymium-doped sodium-yttrium double fluoride Nd3+:Na0.4Y0.6F2.2 crystals

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 sigma (a) = 0.96 x 10(-20) cm(2) and the bandwidth is Delta lambda = 17.5 nm. The most intense luminescence band is located at 1.05 mum and the radiative rime of the F-4(3/2) level is to = tau (exp) similar to 60 mus. It is shown that the P-2(3/2) and D-4(3/2) levels of Nd3+:NYF crystals are also radiative with lifetimes tau (exp) equal to similar to 110 and 9.5 mus, respectively. However, these radiative transitions are partially quenched due to nonradiative relaxation. The intensity parameters Omega (t) are determined by the Judd-Ofelt method to be Omega (2) = 1.18 x 10(-20), Omega (4) = 1.55 x 10(-20), and Omega (6) = 2.85 x 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. (C) 2000 MAIK "Nauka/Interperiodica".