Green emission and laser properties of Ho3+ doped titano lead borate (TLB) glasses for colour display applications

Abstract

A novel Ho3+ ion doped titano lead borate (TLB) glass with chemical composition (55-x) H3BO3 ​+ ​15Li2CO3 ​+ ​17CaF2 ​+ ​8PbO ​+ ​5TiO2 ​+ ​xHo2O3 (x ranged from 0.1 to 2.0 ​wt %, and was referred to as Ho3+ ions concentration) was prepared with melt quenching, and its physical parameters and spectroscopic properties were characterized. Both the density and the refractive index of the glass increase with Ho3+ ion concentration. There are eleven obvious absorption bands in each UV–Vis–NIR spectrum, and their intensity increases linearly with Ho3+ ion concentration. The glass’s direct optical band gap increases with Ho3+ ion concentration, while its Urbach’s energy linearly decreases. Judd-Ofelt (JO) intensity parameters (Ωλ, λ ​= ​2, 4, 6) were evaluated to study the bonding nature of Ho3+ ion and its surrounding ligand, Ω2>Ω4>Ω6; and no matter Ω2 or Ω4 or Ω6 first increases and then decreases with Ho3+ ion concentration, and gets the maximum value at 1.0 ​wt %. The glass photoluminescence spectrum has five visible emissions, one blue, one green and three red; the green one at 546 ​nm from 5F4→5I8 transition has the highest intensity. It also has a near infra-red (NIR) emission at 1195 ​nm from 5I6→5I8 of lasing transition. The spectroscopic quality factor (χ ​= ​Ω4/Ω6), colour chromaticity coordinates (x, y), the correlated colour temperature (CCT) and the colour purity (CP) were calculated. The radiative properties such as the branching ratio (βR), the lifetime (τexp), the stimulated emission cross-section (σPE), the gain bandwidth (σpE×Δλeff) and the optical gain parameter (σpE×τexp) have also been calculated with JO parameters. 1HoTLB glass has the most competitive parameters, such as 64% of quantum efficiency, 80% of CP, and 129.37×10−22 ​cm2 of visible σPE. The photoluminescence decay time profile shows a non-exponential behavior for all the glasses. The glass’s quantum efficiency increases first and then decreases with Ho3+ ion concentration increase, while the fluorescence lifetime is just the opposite. And 1HoTLB glass has the highest quantum efficiency and the shortest lifetime. The spectroscopic potencies in the visible and NIR emissions suggest that this glass could be used in continuous wave laser, green lighting and multi-colour display.