Inhomogeneous-Broadening-Induced Intense Upconversion Luminescence in Tm3+ and Yb3+ Codoped Lu2O3-ZrO2 Disordered Crystals.

Near-infrared (980 nm) to near-infrared (800 nm) and blue (490 nm) upconversion has been studied in 0.2% Tm3+ and 10% Yb3+ codoped Lu2O3-ZrO2 solid solutions as a function of the ZrO2 content in the range of 0-50%, prepared by a high-temperature solid-state reaction. The continuous enhancement of upconversion luminescence is observed with increasing ZrO2 content up to 30%. Analyses of the Yb3+ emission intensity and lifetime indicate enlarged absorption of a 980 nm excitation laser and enhanced energy transfer from Yb3+ to Tm3+ with the addition of ZrO2. The spectrally inhomogeneous broadening of the dopants in this disordered solid solution is considered to play the main role in the enhancement by providing better matches with the excitation laser line and increasing the spectral overlap for efficient energy transfer from Yb3+ to Tm3+. In addition, the inhomogeneous broadening is also validated to improve energy migration among Yb3+ ions and energy back transfer from Tm3+ to Yb3+. Hence, it is understandable that a drop in the upconversion luminescence intensity occurs as the concentration of ZrO2 is further increased from 30% to 50%. This work indicates the possibility of disordered crystals to achieve intense upconversion luminescence for biological and optoelectronic applications.