Blue,green and red up-conversion luminescence at around 490,545 and 650 nm,which result from the Ho^(3+):~5F_3(?)~5I_8,(~5F_4,~5S_2)(?)~5I_8 and ~5F_5(?)~5I_8 transitions,respectively,were observed in Nd^(3+)-Ho^(3+) co-doped oxyfluorotellurite glasses under 800 nm excitation.Among these up-conversion luminescence,the green emission was extremely strong and the blue and red emission intensities were very weak.Selectively strong green up-conversion luminescence of these glasses indicate a high possibility for realizing a green up- conversion laser.Up-conversion processes for the blue,green and red emissions are two-photon processes assisted by Nd^(3+)→Ho^(3+) energy transfer.It is proposed that the up-conversion mechanism for the blue and green emissions is different from that for the red emission.The respective mechanisms are discussed.
Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·(1.95-x)GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 (x=0.02,0.05,0.08,0.11,0.14,0.17)in mole percent.Intense blue(476 nm),green(524 and 546 nm)and red(658 nm)emissions which identified from the 1G 4 →3H 6 transition of Tm3+and the(2H 11/2 ,4S 3/2 )→4I 15/2 ,4F 9/2 →4I 15/2 transitions of Er3+,respectively,were simultaneously observed under 980 nm excitation at room temperature.The results show that multicolor luminescence including white light can be adjustably tuned by changing doping concentrations of Er3+ion or the excitation power.In addition,the energy transfer processes among Tm3+,Er3+and Yb3+ions,and up-conversion mechanisms are discussed.
In vitro dissolution kinetics of a-tricalcium phosphate (α-TCP) cement andα-TCP cement containing tetracycline Hydrochloride(TTCH) were studied in the present paper.It shows that dissolution process ofα-TCP cement and TTCH-loadedα-TCP cement accords with Avrami dissolution kinetics model: x=1-exp(-kt^n),and Avrami constant n is 0.5 and 0.4 respectively,which means dissolution process is diffusion control.Apparent dissolution activation energy ofα-TCP cement and TTCH-loadedα-TCP cement is about 9.87 kJ/moland 7.17 kJ/mol respectively.Comparing withα-TCP cement,activation energy and Avrami constant of TTCH-loadedα-TCP cement decrease slightly,but its [Ca^(2+)] solubility decreases from 40 ppm to 11.5 ppm, which could result from the change of interfacial property and morphology of hydrated apatite crystal caused by absorption of TTCH on the apatite.
