EPR, optical absorption and luminescence studies of Cr super(3+)-doped antimony phosphate glasses

Antimony phosphate glasses (SbPO) doped with 3 and 6 mol% of Cr super(3+) were studied by Electron Paramagnetic Resonance (EPR), UV-VIS optical absorption and luminescence spectroscopy. The EPR spectra of Cr super(3+)-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:Cr super(3+) presented four characteristics bands at 457, 641, 675, and 705 nm related to the transitions from super(4)A sub(2)(F) to super(4)T sub(1)(F), super(4)T sub(2)(F), super(2)T sub(1)(G), and super(2)E(G), respectively, of Cr super(3+) ions in octahedral symmetry. Optical absorption spectra of SbPO:Cr super(3+) allowed evaluating the crystalline field Dq, Racah parameters (B and C) and Dq/B. The calculated value of Dq/B = 2.48 indicates that Cr super(3+) ions in SbPO glasses are in strong ligand field sites. The optical band gap for SbPO and SbPO:Cr super(3+) were evaluated from the UV optical absorption edges. Luminescence measurements of pure and Cr super(3+)-doped glasses excited with 350 nm revealed weak emission bands from 400 to 600 nm due to the super(3)P sub(1) arrow right super(1)S sub(0) electronic transition from Sb super(3+) ions. Cr super(3+)-doped glasses excited with 415 nm presented Cr super(3+) characteristic luminescence spectra composed by two broad bands, one band centered at 645 nm ( super(2)E arrow right super(4)A sub(2)) and another intense band from 700 to 850 nm ( super(4)T sub(2) arrow right super(4)A sub(2)).