phase-dependent-control-trap-depth-persistent-luminescence-strontium

Phase-Dependent Control of Trap Depth and Persistent Luminescence in Strontium Aluminate Phosphors

Persistent luminescent (PersL) materials have garnered significant attention for applications in visualization, signaling, bioimaging, and ...

PSL University, Chimie ParisTech, IRCP-CNRS

The development of probes for biomolecular imaging and diagnostics is a very active research area. Among the different imaging modalities, optics emerged since it is a noninvasive and cheap imaging technique allowing real time imaging. In vitro, this technique is very useful however in vivo, fluorescence suffers from low signal-to-noise ratio due to tissue autofluorescence under constant excitation. To address this limitation, novel types of optical nanoprobes are actually being developed and among them, persistent luminescence nanoparticles (PLNPs), with long lasting near-infrared (NIR) luminescence capability, allows doing optical imaging without constant excitation and so without autofluorescence. This review will begin by introducing the physical phenomenon associated to the long luminescence decay of such nanoprobes, from minutes to hours after ceasing the excitation. Then we will show how this property can be used to develop in vivo imaging probes and also more recently nanotheranostic agents. Finally, preliminary data on their biocompatibility will be mentioned and we will conclude by envisioning on the future applications and improvements of such nanomaterials.

Imaging and therapeutic applications of persistent luminescence nanomaterials.

ZnGaO:Cr, owing to its persistent luminescence properties in the deep red range, is an exceptional material in view of foreseen in vivo imaging applications. In the present work, we report the elaboration process and detailed investigations of the optical properties of nano glass-ceramics composed of spinel ZnGaO:Cr,Yb nanocrystals embedded in a transparent, silica rich, glass matrix. The as-prepared materials show good incorporation of the dopants in the crystallites leading in both Cr and Yb emissions. These emissions occur while exciting in the Cr bands, indicating an energy transfer process from Cr to Yb. Furthermore, excitation in the Yb band in the near-infrared (NIR) range suggests an interesting up-conversion process, which promotes the Cr emission. Persistent luminescence of both Cr and Yb doping ions can be activated by charging the Cr excitation bands, leading to persistent luminescence of zinc gallate nanocrystals in both first and second biological windows. The influence of Yb co-doping on persistent luminescence properties has been investigated by persistent luminescence decay profiles and thermoluminescence studies. Indeed, thermoluminescence glow curves of Yb exhibit similar shape to those of Cr but appear broader and shifted towards higher temperatures. This temperature shift may be explained by the temperature dependence of the involved energy transfer process.

Persistent energy transfer in ZGO:Cr,Yb: a new strategy to design nano glass-ceramics featuring deep red and near infrared persistent luminescence.

Co-doped hexagonal Sr1-x/2Al2-xSixO4:Eu2+,Dy3+ (0.1 ≤ x ≤ 0.5) transparent ceramics have been elaborated by full glass crystallization. The compositions with low SiO2 content (x ≤ 0.4) require fast quenching conditions to form glass, i.e. specific elaboration processes such as aerodynamic levitation coupled to laser heating, whereas the x = 0.5 glass composition can be prepared on a large scale by the classic melt-quenching method in commercial furnaces. After a single thermal treatment, the resulting SrAl2O4-based transparent ceramics show varying photoluminescence emission properties when x increases. These variations are also observable in persistent luminescence, resulting in an afterglow colour-tuning ranging from green to light blue. Afterglow excitation spectra highlight the possible activation in the visible range of the obtained persistent luminescence. Indeed, persistent luminescence of hexagonal Sr0.75Al1.5Si0.5O4:Eu2+,Dy3+ large transparent ceramics has been successfully charged using a typical smartphone low power white light source. Moreover, thermoluminescence glow curves of samples containing different Dy3+ doping concentrations are studied to gain insights regarding the traps' origin and depth. Coupling thermoluminescence results together with luminescence thermal quenching and band gap calculations appear useful to understand the charge trapping and detrapping evolution with the material composition. Varying the Si-content in hexagonal Sr1-x/2Al2-xSixO4:Eu2+,Dy3+ compounds appears as a promising strategy to obtain transparent materials with tuneable green to light blue persistent luminescence.

Hexagonal SrAlSiO:Eu,Dy transparent ceramics with tuneable persistent luminescence properties.

Mechanoluminescence (ML) phosphors have found various promising utilizations such as in non-destructive stress sensing, anti-counterfeiting, and bio stress imaging. However, the reported NIR MLs have predominantly been limited to bulky particle size and weak ML intensity, hindering the further practical applications. For this regard, a nano-sized ZnGaO: Cr NIR ML phosphor is synthesized by hydrothermal method. By improving the synthesis method and regulating the chemical composition, the NIR ML (600-1000 nm) intensity of such nano-materials has been further enhanced about four times. The reasons for the ML performance difference between micro-/nano- sized phosphors also have been preliminarily analyzed. Additionally, this work probes into the ML mechanism deeply in traps' aspect from band structure and defect formation energy, which can supply significant references for a new approach to develop efficient NIR ML nanoparticles. Finally, due to excellent tissue penetration capability, nano-sized ZnGaO:Cr NIR ML phosphor shows great potential applications in biomedical fields such as for the detection of clinical oral diseases.

Article	Year
Imaging and therapeutic applications of persistent luminescence nanomaterials. Advanced drug delivery reviews\| PubMed ID: 30414492	2019
Persistent energy transfer in ZGO:Cr,Yb: a new strategy to design nano glass-ceramics featuring deep red and near infrared persistent luminescence. Physical chemistry chemical physics : PCCP\| PubMed ID: 31461089	2019
Hexagonal SrAlSiO:Eu,Dy transparent ceramics with tuneable persistent luminescence properties. Dalton transactions (Cambridge, England : 2003)\| PubMed ID: 33179669	2020
Near-Infrared Mechanoluminescence from Cr-Doped Spinel Nanoparticles for Potential Oral Diseases Detection. Small (Weinheim an der Bergstrasse, Germany)\| PubMed ID: 39126362	2024

Bruno Viana

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