Pure Boric Acid Does Not Show Room‐Temperature Phosphorescence (RTP)

Abstract

Boric acid (BA) has been used as a transparent glass matrix for optical materials for over 100 years. However, recently, apparent room‐temperature phosphorescence (RTP) from BA (crystalline and powder states) was reported (Zheng et al., Angew. Chem. Int. Ed. 2021, 60, 9500) when irradiated at 280 nm under ambient conditions. We suspected that RTP from their BA sample was induced by an unidentified impurity. Our experimental results show that pure BA synthesized from B(OMe)3 does not luminesce in the solid state when irradiated at 250–400 nm, while commercial BA indeed (faintly) luminesces. Our theoretical calculations show that neither individual BA molecules nor aggregates would absorb light at >175 nm, and we observe no absorption of solid pure BA experimentally at >200 nm. Therefore, it is not possible for pure BA to be excited at >250 nm even in the solid state. Thus, pure BA does not display RTP, whereas trace impurities can induce RTP.

Fast photostimulus-responsive ultralong room-temperature phosphorescence behaviour of benzoic acid derivatives@boric acid

“…Comparatively, pure BA powder only showed negligible fluorescence emission at 431 nm and almost invisible phosphorescence, which was also reported by Marder's group. 59 BADs@BA exhibited gradually increasing bright blue fluorescence under handy UV lamp irradiation at 254 nm, while bluish violet ultralong phosphorescence appeared for several seconds after switching off the lamp (Fig. 1b and 2a).…”

Competition between ultralong organic phosphorescence and thermally activated delayed fluorescence in dichloro derivatives of 9-benzoylcarbazole

“…10 A similar mechanism explains the ultralong phosphorescence in commercial boric acid, for which luminescence is completely absent when pure lab-synthesised boric acid is irradiated under UV light. 67…”

“…10 A similar mechanism explains the ultralong phosphorescence in commercial boric acid, for which luminescence is completely absent when pure lab-synthesised boric acid is irradiated under UV light. 67 In previous work, we investigated the effect of Bd impurities in Cz crystal on its excited state mechanisms. We found that Cz doped with Bd shows red-shifted fluorescence with the emission localised on the impurity.…”

Role of Carbonyl Distortions Facilitating Persistent Room-Temperature Phosphorescence

“…Although many materials that exhibit triplet excitons have been introduced recently, explanations based on assumptions that lack experimental evidence of key physical factors are common in the literature. Corresponding conclusions without identification of the key physical values potentially mislead researchers who are unfamiliar with the field, and indeed the contributions of impurities to persistent RTP are often discussed. − However, evaluating the k nr (RT) of VA based on previous statistical relationships between experimental and calculated data regarding k nr (RT) facilitates reliable conclusions for the k nr (RT) of VA . Because this type of statistical analysis provides physical insights and is useful for addressing potentially misleading conclusions, an analysis of key physical factors from experimental and theoretical standpoints in physical chemistry is important.…”