Polarization and local disorder effects on the properties of Er3+-doped XBi(YO4)2, X = Li or Na and Y = W or Mo, crystalline tunable laser hosts

Pure and Er-doped ([Er](crystal) <= 2.4 X 10(20) cm(-3)), NaBi(WO4)(2) (NBW), NaBi(MoO4)(2), and LiBi(MoO4)(2) crystals have been grown by the Czochralski method. The three crystal hosts have similar structural and optical properties. The noncentrosymmetric space group I (4) over bar (No. 82) crystallographic structure has been established through 300 K single-crystal x-ray and neutron (for NBW only) diffraction. Er3+ energy levels were determined experimentally and simulated in the S-4 symmetry through a crystal-field analysis. With this background, the large spectroscopic bandwidths observed were ascribed to the presence of two 2b and 2d sites for Er3+ and to different short-range Na+ and Bi3+ distributions around both sites. The radiative properties of Er3+ are described by the Judd-Ofelt theory achieving branching ratios and radiative lifetimes for transitions useful as laser channels. The I-4(13/2) -> I-4(15/2) laser channel (lambda approximate to 1.5 mu m) shows a peak emission cross-section sigma(EMI) (lambda approximate to 1530 nm) approximate to 0.5 X 10(-20) cm(2) and a quantum efficiency eta approximate to 0.68 to 0.74. The laser emission is envisaged to be tunable by Delta lambda approximate to 100 nm. (c) 2006 Optical Society of America.