Temperature-dependent photoluminescence study of Pb<sup>2+</sup> doped strontium iodide

Temperature-Dependent Photoluminescence spectra and fluorescence decay time curves for Pb ²⁺ doped SrI ₂ crystals were measured and investigated. Three distinct emissions with different luminescence mechanisms and behaviors are observed in the range 80-300 K. Under the 6S ² -6S6P interconfiguration excitations for Pb ²⁺ ions, Pb ²⁺ doped SrI ₂ crystal presents an intense, asymmetric, and broad emission corresponding to ³ P _{0, 1} → ¹ S ₀ 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 ³ P ₁ → ¹ S ₀ transition over the ³ P ₁ → ¹ S ₀ 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 ³ P _{0, 1} → ¹ S ₀ transitions of Pb ²⁺ 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 ³ P ₁ → ¹ S ₀ transition. Under the non 6S ² -6S ¹ 6P ¹ 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.