EXPRESS: A Novel Er3+ Doped SiO2-Al2O3-Na2O-CaO Glass Materials for Near-Infrared Photonic Applications: Unveiling the Structural, Optical Absorption, Optical Bandgap Energy, Photoluminescence, and Spectroscopic Properties.

Although Er3+-doped glasses have been shown to be capable of producing an excellent combination of near-infrared and visible emissions; a number of conventional glass matrices are hampered by low levels of solubility for rare earths, concentration quenching, and poor structural uniformity which result in lower than desired optical quality. Furthermore, there is still a lack of systematic understanding regarding how modifications to the structure of aluminosilicate glasses influence their spectroscopic properties. Therefore, this investigation sought to develop and optimize a new series of Er3+ doped Al2O3-SiO2-CaO-Na2O aluminosilicate glasses for use as advanced photonic materials, while investigating the relationships between the structure of the glass, the local environment of the rare earth ions within the glass matrix and the overall luminescent response. The glasses were produced via the traditional melt-quenching process and analyzed using Fourier Transform Infrared (FT-IR), optical absorption spectroscopy, Judd-Ofelt (J-O) analysis, and photoluminescence (PL) spectroscopy. Analysis via FT-IR indicated an improvement in the connectivity of the glass structure due to enhancement of both Al-O and O-Si-O vibrational bands present in the glass upon incorporation of Er3+. XRD confirmed the amorphous nature of the samples, while FT-IR analysis showed that increasing Al2O3 enhances structural connectivity within interconnected AlO4 and SiO4 network units. Judd-Ofelt analysis demonstrated the parameter trend Ω2 > Ω4 > Ω6 with the A3 composition achieving the highest Ω2 value indicating elevated site asymmetry and stronger covalency around Er3+ion. Upon 380 nm excitation, the photoluminescence spectra exhibited weak blue, intense green and orange emissions corresponding to the (2H11/2 →4I15/2), (4S3/2 →4I15/2), and (4F9/2 →4I15/2) transitions, respectively, together with a prominent near-infrared emission around 1.55 μm assigned to the (4I13/2 →4I15/2) transition. Additionally, the Judd-Ofelt analysis showed that the A3 glass composition possessed the largest Ω2 value among all compositions investigated, indicating that it had a greater degree of local structural asymmetry and a stronger level of covalency surrounding each Er3+ ion. PL spectral data further demonstrated a strong intensity of green emission that corresponds to the 4S3/2→4I15/2 and 4I13/2→4I15/2 transitions. The radiative lifetime, quantum efficiency, and additional radiative parameters measured for the A3 glass composition also demonstrated that it possessed superior optical properties compared to the other compositions studied. The superior luminescence observed for the A3 glass composition was attributed to a higher degree of dispersion of the rare earth ions throughout the glass matrix, lessened effects of concentration quenching, and an optimal degree of modification of the aluminosilicate network. Overall, these results demonstrate that optimized Er3+ doped aluminosilicate glasses provide good combinations of structural and spectroscopic properties and could therefore serve as suitable materials for use in the production of optical fiber and wave guide amplifiers, integrated photonic circuits, eye safe lasers, optical sensors, visible up conversion devices, and future generations of wide band optical communication systems. Hence, the optimized A3 sample exhibited superior radiative properties and enhanced luminescence performance confirming its potential for optical fiber amplifiers, planar waveguides, and photonic systems.