Sol-gel synthesis for stable green emission in samarium doped borosilicate glasses

In this work, novel green luminescent samarium doped-borosilicate glasses synthesized by the sol-gel route are reported. Although synthesis of crack-free monoliths was carried out in acid catalyzed reaction at room temperature with subsequent gelation at 50 degrees C, heating in N-2/H-2 atmosphere activated the luminescence. The results reveal the amorphous nature of glasses with embedded Sm2O3 nanoparticles in the reticular structure. From TEM analysis, the average particle size is estimated to be around 2.7 and 4.1 nm for the glasses without and with Na2O, respectively. The addition of Sm2O3 and Na2O promotes an increase in the glass transition and crystallization temperatures due to the boric anomaly. However, the optical band gap of undoped borosilicate glasses (3.65-3.86 eV) decreases with the addition of Sm2O3 and Na2O (3.39-3.57 eV). Furthermore, the observed green luminescence (545 nm), associated to F-4(3/2) -> H-6(5/2) transition of Sm3+ ions in borosilicate glasses, is found to remain stable during the test period of 6 months. Therefore, glasses with high spectral purity and low-phonon losses have been obtained by easy sol-gel route, which is useful to promote the emergence of spectral transitions of higher energy with respect to the usually reported transitions at 600 nm ((4)G(5/2) -> H-6(7/2)).