\(\text {Er}^{3+}\), \(\text {Nd}^{3+}\), \(\text {Tm}^{3+}\): Up-conversion in Lead Borophosphate Glasses for Visible Emission

To investigate the role of PbO as a former or a modifier and effect of its compositional variation on the physical, structural and optical properties, lithium lead borophosphate glasses were synthesized by melt quenching technique. For the physical properties of the prepared glasses, density was measured using the Archimedes principle, which showed an increasing trend from 3.13 to 4.51 with increasing concentrations of lead oxide. Additionally, other physical parameters were calculated based on the measured density values. The structural analysis were performed through X-ray diffraction and Fourier transform infrared spectroscopy. Lack of sharp and characteristic peaks in the XRD spectra confirmed the non crystalline nature of the prepared glasses. Structural units due to PbO, \(\text {P}_{2}\text {O}_{5}\) ${\text{P}}_2{\text{O}}_5$ and \(\text {B}_{2}\text {O}_{3}\) ${\text{B}}_2{\text{O}}_3$ were identified from the FTIR spectra. Ultraviolet-visible absorption spectroscopy was performed for optical properties and increase in the indirect band gap from 4.80 eV to 4.90 eV was observed. One glass sample was chosen for doping of erbium, neodymium, thulium and ytterbium, for study of their up-conversion properties. The UV-Vis-NIR absorption spectra of erbium, neodymium, and thulium samples were recorded, and wavelength of 980 nm was chosen for excitation. Ytterbium, acting as a sensitizer, facilitated the conversion of the excitation infrared light into visible light. Upon excitation at 980 nm, the erbium-doped sample emitted light at 520 nm, 547 nm, and 665 nm, utilizing excited state up-conversion (ESA) and energy transfer up-conversion (ETU) mechanisms. Similarly, the neodymium-doped sample emitted at 542 nm, 602 nm, and 660 nm, while the thulium-doped sample emitted at 488 nm, 521 nm, and 649 nm. The results of up-conversion indicate that rare earth-doped lithium lead borophosphate glasses are excellent hosts for up-conversion processes.