Time-gated triplet-state optical spectroscopy to decipher organic luminophores embedded in rigid matrices

Abstract

Wet-chemically synthesized inorganic materials often exhibit luminescence behavior. We have recently shown that the amorphous yttrium-aluminium-borate (a-YAB) powders obtained by sol-gel and modified Pechini methods exhibit organic impurities, responsible for their intense visible photoluminescence and phosphorescence afterglow. However, the heterogeneity of impurity organic compounds and difficulties in their intact extraction from the solid inorganic host matrix limit the extraction-based chemical analysis for luminophore identification. Here, we propose a photo-physical route based on time-gated triplet-state optical spectroscopy (TGTSS) to construct the electronic structures of the trapped unknown luminophores, which successfully illustrates the luminescence properties of a-YAB powders in more detail and also provides important insights intrinsic to the nature of the luminophores. The experimental results accompanied with TD-DFT calculations of the theoretical electronic structures thus help us to propose the probable luminophore compounds trapped in rigid a-YAB matrices. We anticipate that the present approach will open new opportunities for analyzing similar complex luminescent materials, including carbon dots, graphene oxides, etc., which is vital for their improvement.

Cathodoluminescence and microstructural analysis of amorphous yttrium-aluminum-borate luminescent powders

“…The dominant blue region emission in the PL has slightly reduced in CL, but it is significantly reduced in the RL spectrum. This is consistent with the fact that the a-YAB powder exhibits several emitting centers with varied energy levels and the relatively deeper penetration depth of the used X-ray radiation (several tens of μm) might induce radiation trapping of higher energy (violet-blue region) emissions in the RL emission signals [15,24]. The penetration depth in CL is expected to be of the order of 3-4 μm at the used electron energy in a-YAB host, so the reabsorption is relatively weaker (Supporting Information, Figure S6).…”

“…The multiple emissions in a-YAB powder arise from different emitting centers, whose relative abundance is controlled by the calcination temperature [15]. This causes the broadening of predominantly intense violet-blue region emission as the calcination temperature increases.…”

“…Each emitting center exhibits fluorescence as well as phosphorescence components, and therefore the complete spectrum becomes an admixture of several emission bands. Based on the time-gated spectroscopy and theoretical modelling using DFT calculations, we could construct the energy level structure of first few prominent emitting centers and identify the higher energy violet-blue region emitting center to be a phenalene based compound [15]. The results also indicated that the primary energy level structure of the other luminescent centers might be similar but with decreasing energy gaps that lead to the red shifted emissions.…”

“…revealed the presence of small polyaromatic hydrocarbons (PAH), which exhibit good correlation with the broadening of the luminescence spectral profiles [2]. A parallel approach using time-gated spectroscopy and energy level modeling hinted to the presence of multiple emitting centers, which undergo a systematic evolution in relative strengths as a function of calcination temperature, thereby causing the spectral broadening [15]. Each emitting center exhibits fluorescence as well as phosphorescence components, and therefore the complete spectrum becomes an admixture of several emission bands.…”

MCaHxF3−x (M = Rb, Cs): Synthesis, Structure, and Bright, Site‐Sensitive Tunable Eu2+ Luminescence

“…Accordingly, with increasing hydride contents in CsCaH x F 3−x , the fraction of longer wavelength emitting sites increases which additionally quenches the 575 nm emission following resonant energy transfer from the 575 nm sites to the red emitting sites. [50] To get further insight on Eu 2+ luminescence in CsCaH x F 3−x solid solution, the luminescence properties were investigated at 4.2 K. Figure 6a presents the PL and PLE of CsCaH 2 F:Eu 2+ (1%) sample at 4.2 K. The PL bands are better resolved and can be distinctively identified. Accordingly, there are four prominent emissions peaking at 578, 647, 705, and 780 nm.…”