EPR, optical absorption and luminescence studies of Cr3+-doped antimony phosphate glasses

Abstract

Antimony phosphate glasses (SbPO) doped with 3 and 6mol% of Cr3+ were studied by Electron Paramagnetic Resonance (EPR), UV–VIS optical absorption and luminescence spectroscopy. The EPR spectra of Cr3+-doped glasses showed two principal resonance signals with effective g values at g=5.11 and g=1.97. UV–VIS optical absorption spectra of SbPO:Cr3+ presented four characteristics bands at 457, 641, 675, and 705nm related to the transitions from 4A2(F) to 4T1(F), 4T2(F), 2T1(G), and 2E(G), respectively, of Cr3+ ions in octahedral symmetry. Optical absorption spectra of SbPO:Cr3+ allowed evaluating the crystalline field Dq, Racah parameters (B and C) and Dq/B. The calculated value of Dq/B=2.48 indicates that Cr3+ ions in SbPO glasses are in strong ligand field sites. The optical band gap for SbPO and SbPO:Cr3+ were evaluated from the UV optical absorption edges. Luminescence measurements of pure and Cr3+-doped glasses excited with 350nm revealed weak emission bands from 400 to 600nm due to the 3P1→1S0 electronic transition from Sb3+ ions. Cr3+-doped glasses excited with 415nm presented Cr3+ characteristic luminescence spectra composed by two broad bands, one band centered at 645nm (2E→4A2) and another intense band from 700 to 850nm (4T2→4A2).