Spectroscopic properties and energy transfer of Nd^(3+)/Ho^(3+)-doped Ga_2O_3-GeO_2 glass by codoping Yb^(3+) ion

This study presented the luminescence properties of Nd^3＋/Yb^3＋/Ho^3＋ dopant ions inside a host based on Ga_2O_3-GeO_2-Li_2O（GGL） glass. The measured differential scanning calorimetry result showed that GGL glass exhibited excellent stability against devitrification with ？T=135 oC. Obvious 543 and 657 nm emissions were observed in Nd^3＋/Ho^3＋-codoped sample. The incorporation of Yb^3＋ into Nd^3＋/Ho^3＋-codoped glass system had resulted in enhanced upconversion emission intensity under the excitation of 808 nm and/or 980 nm laser diode（LD）. The possible mechanisms and related discussions on this phenomenon were presented. It was noted that the presence of Yb^3＋ yielded an enhancement about 7 and 11 times in the 543 and 657 nm emission intensities respectively under 808 nm excitation due to the energy transfer from Nd^3＋ to Ho^3＋ via Yb^3＋ ion. Here Yb^3＋ played a major role as a bridging ion. While enhanced 543 and 657 nm emission intensities under the excitation of 980 nm LD originated from the sensitization effect of Yb^3＋. Our results showed that Nd^3＋/Ho^3＋/Yb^3＋ triply doped GGL glass might be a promising candidate for the development of visible-laser materials.

Preparation and upconversion luminescence of monodisperse Gd_2O_3:Ho^(3+),Yb^(3+)nanocrystals

Gd2O3：Ho^3＋,Yb^3＋ nanocrystals were synthesized via solvothermal method. X-ray diffraction （XRD）, transmission electron microscopy （TEM）, absorption and upconversion spectra were employed to characterize the synthesized nanocrystals. The results of XRD and TEM showed that obtained Gd2O3：Ho^3＋,Yb^3＋ nanocrystals were cubic in crystal structure and uniform spherical in morphology. The average crystallite size was calculated to be 7.5 nm. Green and red up-conversion emissions corresponding to （^5F4, ^5S2）→^5I8 and ^5F5→^5I8 transition were observed upon 980 nm excitation at room temperature. The results indicated that both green and red luminescence were based on the two-photon processes. Laser power and doping concentration dependence of the up- converted emissions were studied to understand the upconversion mechanisms. Excited state absorption and energy-transfer processes were discussed as the possible mechanisms for the visible emissions.