Luminescence efficiency ofFcenters in KI studied by lifetime measurements

Abstract

The luminescence efficiency of isolated F centers in KI was studied as a function of the excitation energy by measuring the lifetime for ordinary luminescence. The emission intensity measured under a pulse excitation was found to obey nonexponential decay. The luminescence efficiency decreases to below unity when the excitation energy exceeds 1.96 eV, which corresponds to the slope position at the higher energy side of an F absorption band. The threshold value for the luminescence efficiency is lower than that previously obtained from cw measurements but close to that predicted theoretically by Leung and Song. We have traced the origin of this difference by performing experiments based on the cw method and found out the reason. It is shown that there is a relationship between quantities obtained by the cw method and those obtained by our lifetime measurement. Our experimental data are thoroughly analyzed using a model for the radiationless process of Leung and Song, which is based on a 1s-2p model. A 1s-2p-2s model is also discussed.We have obtained excitation spectra for fast and slow components from the results of A f and A s shown in Fig. 7͑b͒ by using Eqs. ͑A4͒ and ͑A5͒ in Appendix, in which the number of irradiation times n is 87 and the duration time t p is 4.6 s. They are denoted by I cw,f cal and I cw,s cal respectively, and presented in Fig. 8 as a function of the excitation energy, together with the absorption curve of the F band. We see that I cw,s cal well coincides with the F absorption band except for the high-energy side near the K band. This fact means that I cw,s cal is just the excitation spectrum of slow component and the emission of slow component occurs under thermal equilibrium. The other important fact is that I cw,f cal spectrum with the peak of 2.06 eV is not related to the F absorption band. This result suggests that fast and slow components arise from different sources. The deviation of I cw,s cal from the F band in the high-energy side reflects the decrease in s due to radiationless processes.In Sec. IV E, we will show that I cw,s cal agrees with the excitation spectrum obtained by the cw method. C. Dependence of the fast component's lifetime on F center concentrations and temperatures

Defects in sodalite-group minerals determined from X-ray-induced luminescence

“…However, the lanthanide concentrations of our samples and consistently low (only turquoise sodalite is above limit of detection, Table 2) and a similar centre are observed in synthetic alkali halides when Ce 3+ activation is unfeasible. We note that the lifetime of a few μs measured by Gaft et al (2009) is also consistent with F-centres in alkali halides (Akiyama and Kobashi 2009). However, from a crystal chemical point of view Ce 3+ is not easily accommodated in the sodalite structure and our data (Table 2) and those of Zahoransky et al (2016) show the content of Ce in pink sodalites from Ilímaussaq to be below the limit of detection for laser ablation ICPMS.…”

Dynamics of nuclear wave packets at theFcenter in alkali halides

“…It was shown that the occurrence or absence of luminescence could be predicted on the basis of parameters inferred from optical absorption data[103,104]. The dynamical nonradiative transition has been studied theoretically[105] and experimentally[106,107]. On the other hand, there is another interpretation that the small efficiency of luminescence at the F center in NaBr, NaI is attributed to an ionization to form the F center (an anion vacancy with two trapped electrons) with full efficiency[108].…”