Crystal growth and optical characterization of chromium-doped l-arginine phosphate monohydrate

Abstract

l-arginine phosphate monohydrate single crystals doped with Cr3+ ions (LAP:Cr) were grown by slow cooling method, with dimensions up to 10 × 10 × 8 mm3. Chromium ions induce a drastic reduction of overall growth rate and produce a drastic change in LAP growth morphology. The functional groups of LAP:Cr crystals were confirmed by FTIR analysis and compared with pure LAP. The optical band gap of LAP:Cr was determined from UV-VIS-NIR transmittance spectrum. Optical absorption spectrum at room temperature and 10 K was measured consisting of two large bands due to the 4A2 → 4T2 and 4A2 → 4T1 transitions and a narrower band attributed to the 4A2 → 2E spin-forbidden transition, characteristic of Cr3+ ions. Luminescence spectra of pure and Cr3+-doped samples were collected with excitation at wavelength of 350 nm and 335 nm. Emissions from host LAP matrix and Cr3+ ions were observed. Excited with 350 nm the spectra reveal a broad intense band from 21000 to 26000 cm−1 region due to electronic transition from LAP ligand. The emission spectra of doped sample present two broad bands centered at 12346 cm−1 and 13412 cm−1 from 2E → 4A2 and 4T2 → 4A2 transitions, characteristics of luminescence from Cr3+ ions. From these results the Racah and crystal-field Cr3+ parameters were evaluated and comparing with those obtained in similar systems.