Intense red and green luminescence from holmium activated zinc-sulfo-boro-phosphate glass: Judd-Ofelt evaluation

Abstract

Rare-earth ions doped oxide glasses became prospective for high quality and inexpensive solid state laser development. To fulfill this need, zinc-sulfo-boro-phosphate glasses doped with holmium ions (Ho3+) were synthesized via melt-quenching method. Prepared glasses were characterized using diverse techniques to determine the influence of varied Ho3+ contents on their optical absorption and photoluminescence (PL) emission properties. The main purpose of this paper was to determine the structural and optical correlation in Ho3+ activated phosphate-based glass host involving the red and green lasing potency of holmium. Raman, XPS and FTIR spectra were recorded to analyze the structural properties of the synthesized glasses. Furthermore, Judd-Ofelt (J-O) intensity (Ωλ with λ = 2, 4 and 6) and radiative parameters were calculated. Absorption spectra of the studied glasses disclosed thirteen characteristic peaks associated to the transitions from the lowest electronic energy level (5I8) to various excited levels in Ho3+. The PL spectra of the proposed glasses revealed 3 significant peaks allocated to the 5F4 → 5I8, 5F5 → 5I8 and 5F4 → 5I7 transitions in Ho3+. Revelation of negative bonding parameter values implied the existence of ionic bond between the ligand and Ho3+ in the prepared glass host. Values of Ω2, Ω4 and Ω6 were observed in the range of (5.11–22.62)×10−20 cm2, (9.54–13.79)×10−20 cm2 and (3.71–6.78)×10−20 cm2, respectively. Lower Ω2 value signified the higher symmetry around Ho3+, whereas higher Ω4 and Ω6 values indicated the stronger rigidity of the glass network. The achieved large stimulated emission cross-section for the red and green spectral transitions from Ho3+ ((29.47–46.01)×10−21 cm2 for 5F4 → 5I8, (31.47–39.74)×10−21 cm2 for 5F5 → 5I8 and (13.34–31.63)×10−21 cm2 for 5F4 → 5I7) clearly displayed the lasing effectiveness of the proposed glasses.