Study on the spectroscopic properties of Pb2+ doped SrI2 single crystals

Optical transmission and absorption, radioluminescence, temperature-dependent photoluminescence and fluorescence time profiles of Pb2+ doped SrI2 crystals were investigated. The optical absorption spectrum presents characteristic absorption bands corresponding to the 6S(2)-6S6P transitions of Pb2+ ions and an undetermined absorption band peaking at 435 nm. Radioluminescence at the room temperature displays a broad emission band in 400-800 nm range with absorption dip at 420-450 nm. Three distinct emissions with different luminescence mechanisms and behaviors are observed within the 80-300 K range. Under the 378 nm excitations, Pb2+ doped SrI2 crystal presents an intense, asymmetric, and broad emission corresponding to the P-3(0,1) -> S-1(0) transitions. The thermally active phonon assistant tunneling from the excited states of the lower energy emission (P-3(0) -> S-1(0)) to the excited states of the higher energy emission (P-3(1) -> S-1(0)) is suggested to be responsible for the observed spectral blue-shift with the rising temperature. The thermal quenching activation energy is calculated as 0.50 +/- 0.04 eV for the P-3(1) -> S-1(0) transition. Under the 433 nm excitation, emission bands peaking at 510 nm and 680 nm are observed. The 510 nm emission shows double exponential decay characteristic with decay times varying in ns range, and its intensity gradually reduces with the rising temperature. Radiative transition processes predominate the symmetric 680 nm emission, which thus shows weak thermal quenching. (C) 2014 Elsevier B. V. All rights reserved.