yb3+ doped aluminophosphosilicate fiber preforms have been prepared by modified chemical vapor deposition (mcvd) with organic chelate precursor doping technique (ocd). it was found that the flow ratio of yb(thd)(3)/pocl3 had an important influence on partial crystallization in the preform cores. the wholly transparent core was obtained when the flow ratio of yb(thd)(3)/pocl3 ranged in 0.71: 1-0.82:1. crystallization occurred during etching process when the yb(thd)(3)/pocl3 flow ratio was over 0.83:1, corresponding to a doping ratio of yb2o3/p2o5 larger than 1.01:1, as characterized by electron probe microanalysis (epma). x-ray photoelectric spectroscopy (xps) analysis indicated exsistence of p in the quasi-metaphosphate [po4] bond structures in the crystallized area. raman spectra displayed characteristic peaks of silica glasses except 1330 cm(-1) raman peaks, which can be assigned to p=o bond due to the presence of quasi-metaphosphate [po4] units. when the content ratio of yb2o3/ p2o5 exceeded 1.01: 1, al was depleted and p was enriched, and the yb3+ ions was mainly connected with the quasi-metaphosphate [po4] units, which weakened the role of p and al preventing yb3+ ions clustering. as a result, crystallization occurred. and this schematic glass structural model was proposed for the partially crystallized preform core. (c) 2017 the electrochemical society.