Temperature-dependent photoluminescence study of Pb2+ doped strontium iodide

Temperature-Dependent Photoluminescence spectra and fluorescence decay time curves for Pb²⁺ doped SrI₂ crystals were measured and investigated. Three distinct emissions with different luminescence mechanisms and behaviors are observed in the range 80-300 K. Under the 6S²-6S6P interconfiguration excitations for Pb²⁺ ions, Pb²⁺ doped SrI₂ crystal presents an intense, asymmetric, and broad emission corresponding to ³P_{0, 1} → ¹S₀ transitions. This emission shows obvious thermal quenching characteristics above 250 K and evident temperature-dependent spectral blue shift. The ever-increasing probability ratio of the ³P₁→¹S₀ transition over the ³P₁→¹S₀ transition is suggested to be responsible for the observed spectral blue shift with the temperature rising. Two distinct decay time changing temperature regions (80-250 K and 250-300 K) were observed for emission due to ³P_{0, 1}→¹S₀ transitions of Pb²⁺ ions. The thermal quenching activation energy ΔE, deduced by using the temperature-dependent decay time values from 250 to 300 K and the Arrhenius law, is 0.50 ± 0.04 eV for the ³P₁→¹S₀ transition. Under the non 6S²-6S¹6P¹ transitions related 433 nm excitation, emission bands peaked at 510 nm and 650 nm are observed and their luminescence mechanisms are yet to be revealed. The 510 nm emission shows double exponential decay characteristic with decay times varying in ns range, and its intensity gradually reduces with the temperature rising. Radiative transition processes predominate the symmetric 680 nm emission, which thus shows weak thermal quenching behavior.