Toward Optical Ceramics Based on Yb3+ Rare Earth Ion-Doped Mixed Molybdato-Tungstates: Part II - Spectroscopic Characterization

Investigations of spectroscopic properties were performed for Yb3+-doped solid solutions of chemical formulas based on mixed La2MoWO9 molybdato-tungstate powders that crystallize in the cubic system with the space group P2(1)3 (No. 198) and from which it was also possible to prepare the first translucent optical ceramics. Samples activated by the Yb3+ ion in a wide concentration range were synthesized by three various techniques: high-temperature solid-state reaction, the Pechini method, and the combustion method. The microcrystalline solid solutions obtained by the high-temperature solid-state reaction characterized by intense luminescence are useful for detailed fundamental analysis. The direct excitation of Yb3+ into F-2(7/2) -> F-2(5/2) absorption at 940-980 nm leads to reversed F-2(5/2) -> F-2(7/2) transitions giving Yb3+ emission lines in the 970-1100 rim range. The absorption and emission 0-phonon lines of Yb3+ ions were also used as structural probes at a low temperature, and the conjugation with SEM and TEM techniques was particularly useful here. The multisite character of Yb3+ was confirmed in high-resolution site selective emission spectra. In the case of microcrystalline ceramics, the grains are characterized by a wide 0-phonon line around 976 nm and a high number of multisites and white points by another sharper line around 968 nm. Based on the absorption and emission spectra, the Yb3+ electronic energy level diagram was proposed for the main site. The effect of dopant concentration as well as the grain size influence on the luminescent properties and the decay times were analyzed in order to attempt to understand the concentration quenching mechanism and estimate the parameters useful for a theoretical approach to laser potential first with cubic single crystals and then with cubic transparent ceramics. This second part is related to the spectroscopic properties of powders and microceramic samples analyzed in the first part.