Structural and spectroscopic characteristics of Eu3+ embedded titanium lead phosphate glasses for red luminescence

Abstract

A series of Eu3+ incorporated titanium lead phosphate glasses with the chemical compositions of 1 mol% Eu2O3+ xTiO2+(50–x)PbO+49P2O5 (where x = 1, 3 and 5) have been prepared by the melt quenching procedure. Structural investigations have been performed through XRD and FTIR spectra. Optical properties are investigated by absorption, excitation, photoluminescence emission, decay lifetime and CIE chromaticity measurements. Using absorption transition from 7F0 and 7F1 levels, the nephelauxetic ratio (β) and bonding parameter (δ) are estimated to determine the type of bonding between Eu3+ ions and the surrounding ligands. The absorption as well as the excitation spectra show that the band at 393 nm corresponding to 7F0 → 5L6 transition is very strong. Upon excitation at 393 nm, Eu3+ embedded titanium lead phosphate glasses exhibit maximum emission intensity for 5D0 → 7F2 transition at 611 nm which emits red color. Using Judd-Ofelt (JO) theory, the JO parameters Ω2, Ω4 and Ω6 have been estimated from the absorption and these parameters follow the trend of Ω2>Ω4>Ω6 for all glasses. These JO parameters are used to predict the branching ratio (βR), radiative transition probability (AR), stimulated emission cross-section (σPE) and radiative lifetime (τR). The larger value of spontaneous emission cross-section, suggests that the present glass samples are encouraging materials for Eu3+ embedded optical amplifiers and laser materials. Using the decay profile which shows single exponential, the luminescence decay lifetime of Eu3+ ions for the 5D0 metastable state is evaluated. The fluorescence quantum efficiencies have been evaluated which indicate that the values may be enhanced with the increase of titanium dioxide (TiO2) in the glass matrix. The color purity (CP) of the red emission and correlated color temperature (CCT) of these samples are calculated using the CIE (Commission Internationale de l’Eclairage) chromaticity diagram. Our investigation reveals that the present glasses may be utilized as red luminescent materials and red laser source for 5D0 → 7F2 emission at 611 nm.