Sol–gel synthesis and characterization of fluoride-rich lanthanum-alumino-silicate gels doped with Ce3+ and Ti4

• Published in: Journal of alloys and compounds Vol. 601; pp. 67 - 74
• Main Authors: Lakshminarayana, G., Torres, Joseph A., Lin, Terri C., Kityk, I.V., Hehlen, Markus P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.07.2014; Elsevier
• Subjects: Amorphous materials; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Materials synthesis; materials processing; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Oxyfluoride gels; Photoluminescence; Physics; Rare-earth spectroscopy; Scanning electron microscopy; Sol–gel process; Thermal analysis; Scanning electron microscopy; Amorphous materials; Oxyfluoride gels; Thermal analysis; Sol–gel process; Rare-earth spectroscopy; Differential scanning calorimetry; Volume fraction; Doping; Photoluminescence; Aluminosilicates; Physical gel; XRD; Titanium additions; Scanning thermal microscopy; Cerium additions; Sol―gel process; Absorption spectra; Charge transfer; Glass ceramics; Sol-gel process
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2014.02.098

•Lanthanum-alumino-silicate gels with high fluorine content are synthesized.•Trifluoroacetic acid (TFA) is used as the fluorine source in a sol–gel process.•Thermal decomposition of TFA prevents the conversion of gels to monolithic glasses.•The Ce-doped gels show photoluminescence in the blue spectral region. A series of lanthanum-alumino-silicate gels doped with Ce3+ (0.5–10.0mol%) and Ti4+ were synthesized by a sol–gel process using trifluoroacetic acid (TFA) as a fluorine source. The structural (X-ray diffraction, scanning electron microscopy), thermal (differential scanning calorimetry), and optical (absorption, photoluminescence, photoluminescence-excitation) properties were investigated. A high fluorine content of up to 22.3at.% was measured in the dried gels, significantly exceeding the ⩽5at.% fluorine content of earlier studies. The monolithic gels were transparent, amorphous, and stable up to 250–300°C. However, the gels lost their structural integrity at temperatures above 315°C due to the thermal decomposition of TFA. The sol–gel route using TFA as a fluorine source is therefore not a viable route for the preparation of nanostructured glass ceramics containing a high volume fraction of crystalline LnF3. All Ce3+-doped gels showed luminescence in the blue spectral region. Gels containing Ti4+ had an additional strong oxygen-to-metal charge transfer transition that competed with the Ce3+ optical excitation and led to overall lower emission intensity. The measured luminescence intensity of all gel compositions decreased with increasing Ce3+ concentration as a result of increased reabsorption of Ce3+ emission by other Ce3+ ions in the gel as well as energy migration among Ce3+ ions to quenching sites.