Up- and down-conversion photoluminescence properties of Ho2O3 doped YbAG single crystals prepared by optical floating zone method

Abstract

Single crystals of garnets with composition Yb2.96-xYxHo0.04Al5O12 (x = 0, 2.92, 2.96) were grown by optical floating zone method, and shown by XRD measurements to be in the cubic phase. EDS spectra show that Ho3+ and Yb3+ were homogenously distributed in the structure. As shown by the transmission and absorption spectra, the Yb2.96-xYxHo0.04Al5O12 crystals are highly transparent and can function as excellent optical crystals. Compared to the Y2.96Ho0.04Al5O12 crystal, the Yb2.96Ho0.04Al5O12 crystal has an additional strong broad absorption in the 836–1070 nm range, which increases its absorption of 980 nm photons. The optical band gaps of the Yb2.96-xYxHo0.04Al5O12 crystals decrease with increasing Yb2O3 concentration. Furthermore, differences with Yb2O3 concentrations in the Yb2.96-xYxHo0.04Al5O12 crystals were observed for the first time in the up- and down-conversion photoluminescence. Under excitation with a 980 nm laser, the up-conversion PL spectra of the Yb2.96-xYxHo0.04Al5O12 crystals show several emission peaks at 548 nm, 665 nm and 775 nm, and their intensities increase with Yb2O3 concentrations. In the Yb2.96Ho0.04Al5O12 crystal, Yb3+ not only is a component of the garnet structure, but it also acts as a sensitizer. In regards of down-conversion, under excitation at 454 nm, the down-conversion PL spectra of the Yb2.96-xYxHo0.04Al5O12 crystals show strong emission peaks at 550 nm, and their intensities decrease with increasing Yb2O3 concentrations, which is considered to be the consequence of increasing matrix density.