Efficient Tm3+ up-conversion in lead borophosphate glasses for visible emission

Abstract

Thulium oxide (Tm2O3) doped lithium lead borophosphate glasses have been synthesised and analysed to probe their structural and luminescence properties. X-ray diffraction data confirmed the non-crystalline nature of the prepared glasses. Participation of Tm2O3 in the structure is established by the variation in density and molar volume with increasing concentration of Tm2O3. Fourier transform infrared spectroscopy revealed the various structural units present due to B2O3, P2O5 and PbO. Ultraviolet-visible near infrared absorption spectra showed peaks/bands at 466 nm (G41), 684 nm (F33), 790 nm (H43) and 1210 nm (H53), originating from ground state H63 of thulium while Ytterbium showed its characteristic peak at 978 nm. Indirect band gap, calculated from Tauc's curve showed decreasing trend with increasing concentration of Tm2O3. The other optical parameters like molar refractivity, molar polarizability, electronic polarizability and dielectric constant also showed variation with increase in concentration of Tm2O3. Judd-Ofelt parameters followed Ω2>Ω4>Ω6 trend and oscillator strengths have also been evaluated. For luminescence studies, upon 790 nm excitation, visible peaks at 454 nm, 485 nm, 529 nm, 624 nm and 665 nm were observed while at 684 nm excitation, wavelength of 542 nm and 610 nm is emitted. Excited state absorption up-conversion mechanism is responsible for the observed visible emission. Commission Internationale de I'Eclairage (CIE) chromaticity coordinates have also been calculated and coordinates lie near the white light region. Up-conversion results indicated that the prepared glasses are potential host for up-conversion and can be used in colour displays.