A novel method for uniform dispersion of the rare earth ions in SiO2 glass using zeolite X

A novel method for uniform dispersion of the rare earth ions in SiO2 glass is presented. Nd doped SiO2 laser glass has been made by aluminum co-doping to avoid quenching due to Nd clustering. Previous works with aluminum co-doping were passive methods because uniform dispersion of the rare earth ions in SiO2 glass depended only on aluminum co-doping effect. Concentration quenching of Nd laser glass is explained by cross-relaxation process and depends on Nd-Nd distance in the glass. The shorter the Nd-Nd distance the stronger is quenching, so the distance should be greater than some minimum. Homogeneous rare earth doped SiO2 glass is achieved by a modified sol-gel method using zeolite X. Zeolite X (Na-86[(AlO2)(86). (SiO2)(106)] . 264H(2)O, faujasite-type structure) is a suitable material because Nd ions are selectively exchanged at the D6R segment structure in zeolite X, and the distance between Nd ions in the D6R is 0.88 nm. This distance is three times larger than the critical range of cross-relaxation process which causes quenching. If the Nd-Nd distance is kept at 0.88 nm, the ratio of cross-relaxation probability to radiative decay probability will be 0.23%. Quantum yield is an adequate quantity for confirming uniform dispersion of the rare earth ions in Nd doped laser media. For a newly prepared Nd doped SiO2 glass using zeolite X, quantum yield increased to 50 +/- 3.4% at 1.0 wt%, while an ordinary produced one was 7 +/- 0.5%. (C) 1997 Elsevier Science B.V.