Optical and scintillation properties of SrI2:Yb2+

• Excitation, emission, and decay time of SrI2:Yb2+ were studied between 78 and 600 K.
• Two Yb2+ emission bands were observed.
• 418 nm emission band is due to spin-allowed transition with 400 ns radiative lifetime.
• 446 nm emission band is due to spin-forbidden transition with 30–200 μs decay time.
• Yb2+ spin-allowed emission is strongly affected by its self-absorption.

The luminescence and scintillation properties of SrI2:0.5%Yb2+ have been investigated. SrI2:Yb single crystals were grown by the vertical Bridgeman method from the melt. They showed a light yield of 38,400 ph/MeV and energy resolution of 12.5% for the 662 keV full absorption peak. Yb2+ photoluminescence intensity and decay time were studied between 78 and 600 K. Two emission bands centered at 418 and 446 nm were observed and ascribed to spin-allowed and spin-forbidden Yb2+ 5d-4f transitions, respectively. Their corresponding room-temperature decay time constants are 710 ns and 77 μs. Both, the emission intensities and the decay time constants vary with temperature. The obtained results were interpreted using a model of self-absorption of Yb2+ emission and a model of non-radiative relaxation of the electron from the low spin to the high spin 4f135d Yb2+ excited states. The radiative lifetime of the low spin Yb2+ excited state was determined as 400 ns.