The nature of the emission center of Eu<sup>2+</sup> in KCaF<sub>3</sub>:Eu<sup>2+</sup> strongly depends on the preparative condi-tions.Experimental results sh
Bayan-Obo ore diposit is known as a superlarge rare earth-niobium-polymetallic-iron ore deposit in theworld today.A great many of mineral species were found the