Comment On 'distribution Of Oxidation States Of Cr Ions In Ca Or Ca/mg Co-doped Cr:y_3al_5o_(12) Single Crystal Fibers With Nitrogen Or Oxygen Annealing Environments' By C.-n. Tsai Et Al. [j. Crystal Growth 310 (2008) 2774]

摘要

In their paper [1], Tsai et al. present a detailed experimental study of chromium oxidation states in Cr-doped YAG (Y_3Al_5O_(12)) crystal fibers, co-doped with Ca or Ca/Mg, which underwent high-temperature annealing in oxygen or nitrogen ambient atmospheres. The purpose of our present communication is to raise some queries, and to point out some errors in the said paper. In Fig. 2 of Ref. [1], an approximate increase in factor 2 in fluorescence emissions of both Cr_(oct)~(3+) and Cr_(tetr)~(4+) ions upon high-temperature annealing (1350 ℃) in an oxygen ambient is measured; (Cr_(oct)~(3+) is a triply-ionized chromium occupying octahedral a-sites, Cr_(tetr)~(4+) is a quarterly ionized chromium occupying tetrahedral d-sites of the YAG lattice). The increase in fluorescence is an obvious measure of a parallel increase in concentration of the said ions.