Dong Yanming

Determination of degree of substitution for N-acylated chitosan using IR spectra

Chitosans with various degrees of deacetylation (D.D.), which were used as standard sample for FTIR determination, were prepared from completely deacetylated chitosan by homogeneous N-acetylation reaction. By combining four probable probe bands, i.e. 1655, 1560, 1380 and 1320 cm−1, eight probable reference bands, i.e. 3430, 2920, 2880, 1425, 1155, 1070, 1030 and 895 cm−1 and two baseline methods, the most suitable ratiosA probe band/A reference band from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to beA 1560/A 2880,A 1560/A 2920 andA 1655/A 3430(A 1560/A 2880 is mostly recommended). The second baseline method, i.e. linking between adjacent two valleys, was better for measuring the absorbances of 1560 and 1655 cm?1 bands. The determination range of the D.D. (1%–100%) covered almost the whole range. The standard curves withA 1560/A 2880 andA 1655/A 3430were also suitable for the determination of degree of substitution of other N-acylated chitosan, such as N-propionyl chitosan, N-butyryl chitosan and N-hexanoyl chitosan.

不同掺杂浓度Tm 3+ ：LiLuF 4 单晶的1800 nm荧光发射

LiLuF4 single crystals doped with molar fractions of 0.45%, 0.90%, 1.63%, and 3.25% (x, molar fraction) Tm3+ ions were fabricated by an improved Bridgman method. Absorption spectra in the 400-2000 nm region of the crystals were measured. The emissions from 1400 to 2000 nm under excitation of an 808-nm laser diode (LD) were carried out and compared. Two emission bands at 1470 and 1800 nm were observed. First, the emission intensity at 1800 nm increased with the increase in Tm3+ concentration, reaching a maximum value when the Tm3+ concentration was ca 0.90%. Thereafter, it decreased considerably as the Tm3+ doping levels further increased to 3.25%. However, the emission intensity at 1470 nm showed the contrary tendency to that at 1800 nm. It was found that the 1800-nm emission lifetime of the Tm3+:F-3(4) manifold systematically decreased with an increase in Tm3+ concentration. The trend in the fluorescent intensity change can be explained by the cross-relaxation (H-3(6), H-3(4)-> F-3(4), F-3(4)) between the Tm3+ ions and the concentration quenching effect of Tm3+. Meanwhile, the emission cross-section was calculated, providing a maximum of 0.392x10(-20) cm(2) at 1890 nm for the 0.90% doped sample. Based on the measured lifetime and calculated radiative lifetime, the largest quantum efficiency between Tm3+ ions reached similar to 120%.