The efficient single-photon upconversion photoluminescence (UCPL) feature of lead halide perovskite semiconductors makes it promising for developing laser cooling devices. This is an attractive potential application, but the underlying physics still remains unclear so far. By using the all-inorganic CsPbX 3 (X = Br, I) nanocrystal samples, this phenomenon was investigated by photoluminescence (PL) and timeresolved PL under different temperatures and various excitation conditions. A broad emission band located at the low-energy side of the free exciton (FE) peak was detected and deduced to be from the self-trapped exciton (STE). The lifetime of STE emission was found to be 171 ns at 10 K, much longer than that of FE. The UCPL phenomenon was then attributed to thermal activation of transformation from STEs to FEs, and the energy barrier was derived to be 103.7 meV for CsPbBr 3 and 45.2 meV for CsPb(Br/I) 3 , respectively. The transformation also can be seen from the fluorescence decay processes.
ObjectiveCurrently, the prevalence of CF (Cognitive Frailty) is not very clear, and the relationship between CF and its associated risk factors has not been accurately evaluated. Therefore, it is necessary to conduct a systematic review and meta-analysis further to understand CF's prevalence and associated factors.MethodsEmbase, PubMed, Web of Science, Ovid, and Cochrane were systematically searched for articles exploring the prevalence of CF, the deadline of searching date was up to March 2021. For the prevalence of CF, the events of CF and the total number of patients in every included study were extracted to estimate the prevalence of CF. For associated factors of CF, Odds Ratios (ORs) with (corresponding) 95% confidence intervals (CIs) were used for estimations.ResultsFirstly, the estimated prevalence of CF I (Cognitive Frailty in the model I) was 16%, 95% CI (0.13–0.19), and the estimated prevalence of CF II (Cognitive Frailty in model II) was 6%, 95% CI (0.05–0.07). Secondly, both lower engagement in activities and age were calculated to be independent risk factors of CF, and the OR (95% CI) was 3.31 (2.28–4.81) and 1.10 (1.04–1.16), respectively. Finally, depression was also a prominent risk factor of CF, with the overall OR (95% CI) as 1.57 (1.32–1.87).ConclusionCF was a high prevalence in community older. The various assessment scales and the different cutoff values of diagnostic criteria would affect the prevalence of CF. Lower engagement in activities, age, and depression was the risky factor of CF.Systematic Review Registrationhttp://www.crd.york.ac.uk/PROSPERO/, identifier: CRD42019121369.
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