In this paper, the upconversion luminescent properties of Y2O3:Er3+(1%)/Yb3+(4%) nanoparticles with different sizes (13−55 nm) and its corresponding bulk material as a function of excitation power were studied under 978-nm excitation. Red (4F9/2 → 4I15/2), green (2H11/2, 4S3/2 → 4I15/2), and blue (2H9/2 → 4I15/2) transitions were observed. The results indicated that the relative intensity of the blue as well as the red to the green increased gradually with decreasing particle size. As a function of excitation power, the slope in the ln−ln plot for the red emission changed between 2.0 and 1.0 and gradually decreased with increasing particle size, which was attributed to competition between linear decay and upconversion processes for the depletion of the intermediate excited states. As the particle size decreased to 13 nm, a three-photon populating process occurred for the green emission. As the excitation power varied in different paths, gradually increasing or gradually decreasing, a hysteresis loop appeared in the power dependence of emission intensity, which was mainly caused by a local thermal effect induced by laser irradiation. The intensity ratio of 2H11/2 → 4I15/2 to 4S3/2 → 4I15/2 (R HS ) varied complicatedly with excitation power, which was theoretically explained considering the thermal distribution and relaxation processes. Two novel cross-relaxation paths were proposed on the basis of the variation of R HS under excitation at different wavelengths, 488 and 978 nm.

In this paper, the upconversion luminescent properties of Gd2O3:Er3+,Yb3+ nanowires as a function of Yb concentration and excitation power were studied under 978-nm excitation. The results indicated that the relative intensity of the red emission (4F(9/2)-4I(15/2)) increased with increasing the Yb3+ concentration, while that of the green emission (4S(3/2)/2H(11/2)-4I(15/2)) decreased. As a function of excitation power in ln-ln plot, the green emission of 4S(3/2)-4I(15/2) yielded a slope of approximately 2, while the red emission of 4F(9/2)-4I(15/2) yielded a slope of approximately 1. Moreover, the slope decreased with increasing the Yb3+ concentration. This was well explained by the expanded theory of competition between linear decay and upconversion processes for the depletion of the intermediate excited states. As the excitation power density was high enough, the emission intensity of upconversion decreased due to thermal quenching. The thermal effect caused by the exposure of the 978-nm laser was studied according to the intensity ratio of 2H(11/2)-4I(15/2) to 4S(3/2)-4I(15/2). The practical sample temperature at the exposed spot as a function of excitation power and Yb3+ concentration was deduced. The result indicated that at the irradiated spot (0.5 x 0.5 mm2) the practical temperature considerably increased.

A bio-based epoxy resin (denoted TEIA) with high epoxy value (1.16) and low viscosity (0.92 Pa s, 258C) was synthesized from itaconic acid and its chemical structure was confirmed by 1H NMR and 13C NMR spectroscopy. Its curing reaction with poly(propylene glycol) bis(2-aminopropyl ether) (D230) and methyl hexahydrophthalic anhydride (MHHPA) was investigated. For comparison, the commonly used diglycidyl ether of bisphenol A (DGEBA) was also cured with the same curing agents. The results demonstrated that TEIA showed higher curing reactivity towards D230/MHHPA and lower viscosity compared with DGEBA, resulting in the better processability. Owing to its high epoxy value and unique structure, comparable or better glass transition temperature as well as mechanical properties could be obtained for the TEIA-based network relative to the DGEBA-based network. The results indicated that itaconic acid is a promising renewable feedstock for the synthesis of bio-based epoxy resin with high performance.