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Synthesis and Characterization of Triply Doped Nano-Composite Alumina-Phospho- Silicates SiO<sub>2</sub>-P<sub>2</sub>O<sub>5</sub>-Al<sub>2</sub>O<sub>3</sub> with Er<sup>3+</sup>, Sm<sup>3+</sup> and Yb<sup>3+</sup> Ions Prepared by Sol Gel Technique in Two Different Forms Thin Film and Monolith — Oak Academic Publishing