Tm~(3+)/Ho~(3+)/Yb~(3+) codoped tellurite glass for multicolor emission - Structure, thermal stability and spectroscopic properties

摘要

Tm~(3+), Ho~(3+) and Yb~(3+) codoped tellurite glasses (TeO_2-Bi_2O_3-ZnO-Na_2O) were prepared using conventional melt-quenching technique to realize the sensitized near-infrared to visible multicolor upconversion emission. The X-ray diffraction (XRD) curves, Raman spectra, differential scanning calorimeter (DSC) curves, absorption spectra and visible upconversion emission spectra were measured to characterize the structure nature, thermal stability and upconversion spectroscopic properties of rare earth (RE) codoped glass samples. Upon the excitation of 980 nm laser diode (LD), the multicolor upconversion emissions were experimentally observed from the prepared glass samples owing to the intense blue (~477 nm) upconversion fluorescence of Tm~(3+) and green (~544 nm) and red (~657 nm) upconversion emissions of Ho~(3+), which have been attributed to the result of the multi-step energy transfer (ET) from Yb~(3+) to Tm~(3+) (and Ho~(3+)) and excited state absorption (ESA). The ET mechanism between Yb~(3+):~2F_(5/2) and Tm~(3+):~3H_5 (and Ho~(3+):~5I_6) levels were further investigated by calculating the micro-parameters (energy transfer coefficient Cda and critical radius R_c). In addition, the glass transition temperature (T_g) increases with the RE doped concentration and the estimated difference (AT) between the onset crystallization temperature (T_x) and the glass transition temperature (T_g) for all glass samples is larger than 140℃, while the glass structure maintains the amorphous nature. The excellent thermal stability and multicolor emission characteristics with RE doped concentration indicate that the studied Tm~(3+)/Ho~(3+)/Yb~(3+) codoped tellurite glasses could be used in the fields of solid state multicolor displays and illumination devices.