Luminescent, semiconducting, thermal, and structural performance of Ho3+-doped lithium borate glasses with CaF2 or MgF2

Abstract

Multicomponent lithium borate glasses containing either CaF2 or MgF2 and doped with 0.125 → 0.5% Ho2O3 replacing Li2O were prepared by the melting and annealing technique. The optical, FTIR, photoluminescence spectral and thermal properties of the prepared glasses were examined. The glasses were subjected to the controlled heat treatment two-step regime to be converted to their corresponding glass–ceramics. X-ray diffraction studies indicate the separation of different crystalline phases upon heat treatment in accordance with the presence of either CaF2 or MgF2. The optical spectral measurements of the two undoped glasses show a prominent UV absorption which is due to unavoidable contaminated trace iron impurities, while Ho2O3-doped glasses show additional extended visible–near IR absorption peaks which are related to absorption of Ho3+ ions. Structural FTIR measurements indicate the appearance of nearly similar condensed vibrational bands within the range 400–1600 cm−1 which are correlated with the presence of both triangular and tetrahedral borate groups within their distinct varying wavenumbers. The IR spectra of the glass–ceramic derivatives resemble to a large extent that for their parent glasses with minor variations. The photoluminescence (PL) spectra reveal four distinct excitation peaks within the range 365 → 453 nm and two emission peaks at about 480 and 575 nm. The glass–ceramics PL spectra show minor variations. The thermal expansion curves of the selected undoped and high 0.5 Ho2O3-doped glass from the two studied series show comparable thermal parameters revealing some variations within the thermal data in accordance with the suggested different housing behaviors of constitutional MgF2 or CaF2. The calculated optical parameters data involving the optical bandgap, Urbach energy, and refractive index are assumed to be correlated with the constitutional network structure of glass and its change with variations in the glass composition or percent of dopant oxide.