Room-Temperature Phosphorescent Organic-Doped Inorganic Frameworks Showing Wide-Range and Multicolor Long-Persistent Luminescence

Abstract

Long-persistent luminescence based on purely inorganic and/or organic compounds has recently attracted much attention in a wide variety of fields including illumination, biological imaging, and information safety. However, simultaneously tuning the static and dynamic afterglow performance still presents a challenge. In this work, we put forward a new route of organic-doped inorganic framework to achieve wide-range and multicolor ultralong room-temperature phosphorescence (RTP). Through a facile hydrothermal method, phosphor (tetrafluoroterephthalic acid (TFTPA)) into the CdCO₃ (or Zn₂(OH)₂CO₃) host matrix exhibits an excitation-dependent colorful RTP due to the formation of diverse molecular aggregations with multicentral luminescence. The RTP lifetime of the doped organic/inorganic hybrids is greatly enhanced (313 times) compared to the pristine TFTPA. The high RTP quantum yield (43.9%) and good stability guarantee their easy visualization in both ambient and extreme conditions (such as acidic/basic solutions and an oxygen environment). Further codoped inorganic ions (Mn²⁺ and Pb²⁺) afford the hybrid materials with a novel time-resolved tunable afterglow emission, and the excitation-dependent RTP color is highly adjustable from dark blue to red, covering nearly the whole visible spectrum and outperforming the current state-of-the-art RTP materials. Therefore, this work not only describes a combined codoping and multicentral strategy to obtain statically and dynamically tunable long-persistent luminescence but also provides great opportunity for the use of organic-inorganic hybrid materials in multilevel anticounterfeiting and multicolor display applications.

Figure 1

(a) Doped structures of Cd-TFTPA/NH₄F, Cd/Mn-TFTPA/NH₄F, Cd/Pb-TFTPA/NH₄F, and Zn-TFTPA/NH₄F samples as well as their corresponding long-persistent emission images under various excitation wavelengths. (b) The proposed mechanism of hybrid material for multicolor ultralong phosphorescence with the change of excitation wavelengths. The triplet excitons are generated from the singlet excitons through the intersystem crossing, enabling molecular phosphorescence owing to the strict suppression of the molecular motion by the inorganic matrix framework. The formation of different arrangements and stacking modes can induce different triplet excitons and lead to different phosphorescence.

Scheme 1

Synthetic routes to (a) Cd-TFTPA, (b) Cd-TFTPA/NH₄F, Cd/Pb-TFTPA/NH₄F, and Cd/Mn-TFTPA/NH₄F.

Figure 2

Photoluminescence characterization of Cd-TFTPA/NH₄F powder under ambient conditions. (a) The URTP spectra of the Cd-TFTPA/NH₄F powder under the excitation at 260 nm (blue) and 360 nm (green), respectively. (b) Excitation-phosphorescence mapping of powder under ambient conditions. (c, d) Decay curves of Cd-TFTPA/NH₄F at 417 nm and 533 nm. (e) Excitation-dependent phosphorescence spectra of Cd-TFTPA/NH₄F. (f) CIE coordinate diagram of Cd-TFTPA/NH₄F by changing the excitation wavelengths.

Figure 3

Photoluminescence characterization of Cd/Mn-TFTPA/NH₄F powder under ambient conditions. (a) The URTP spectra of the Cd/Mn-TFTPA/NH₄F powder under the excitation at 260 nm (blue) and 360 nm (red), respectively. (b) Excitation-phosphorescence mapping of powder under ambient conditions. (c, d) Decay curves of Cd/Mn-TFTPA/NH₄F at 417 nm, 520 nm, and 614 nm. (e) Excitation-dependent phosphorescence spectra of Cd/Mn-TFTPA/NH₄F. (f) CIE coordinate diagram of Cd/Mn-TFTPA/NH₄F by changing the excitation wavelengths.

Figure 4

Photographs of the RTP materials taken before and after turning off of the different excitation wavelengths (254 nm and 365 nm) in the scale from 0 to 2.5 s.

Figure 5

Schematic diagram depicting the evolution from triple information encryption to decryption.

Figure 6

The application of Cd/Mn-TFTPA/NH₄F in security protection.