Structural correlation to linear and non-linear optical properties of Bi3+ ion doped Li2O–SrO–B2O3 glasses: Optical switching and limiting applications

A series of bismuth doped lithium strontium borate glasses are synthetized using melt-quench technique. Compositional modification resulted in the maximum refractive index (2.306) and lowest optical bandgap (3.36 eV) for 2 mol% of Bi2O3. Raman as well as FTIR investigations reveal the presence of diborate, dipentaborate and metaborate ring type structural units and structural interconversions occur between diborate and metaborate rings. These structural interconversions are in support of the trends observed in linear and non-linear optical properties. Photoluminescence spectra reveal a prominent emission peak around 572 nm corresponding to the 2P3/2 → 2P1/2 transition. Commission Internationale de I'Eclairage (CIE) and correlated colour temperature (CCT) studies indicate the glasses emit greenish-yellow light around 7172 K. Z-scan approach is utilised to examine non-linear optical properties with a nanosecond pulsed laser operating at 532 nm. Z-scan investigation revealed good optical nonlinearity in all the glasses. Open aperture normalized transmittance spectra is used to evaluate the values of non-linear absorption coefficient (ꞵ) and optical limiting. ꞵ is in the range of 0.42–3.2x10−10 mW−1 and optical limiting values are in the range of 1.642–2.078x1012 Wm−2. Z-scan studies reveal RSA and RSA to SA (W- patterns) which suggests that the investigated glasses show saturable absorption (SA) as well as reverse saturable absorption (RSA) pattern. According to these findings, the glasses under investigation are promising materials for solid state lasers, greenish-yellow LEDs, compositional tuning optical switching and limiting applications.