Extending Afterglow of Ga₂O₃ Nanocrystals by Dy³⁺ Dopant-Induced Carrier Trapping: Toward Design of Persistent Colloidal Nanophosphors

Abstract

Design and preparation of persistently luminescent nanostructured phosphors are of a significant interest in lighting, photonic, and photovoltaic technologies. However, afterglow generally occurs in bulk phosphors synthesized by high-temperature solid-state reactions. Here, we report the synthesis of colloidal Dy 3+doped γ-phase Ga 2 O 3 nanocrystals and demonstrate an extension of the lifetime of nanocrystal emission arising from native-defect-based donor−acceptor pair recombination, relative to undoped nanocrystals. Using temperature-dependent photoluminescence measurements, we show that Dy 3+ dopants reside in the vicinity of nanocrystal surfaces and generate trap states that are significantly shallower than donor states originated by the presence of oxygen vacancies in Ga 2 O 3 nanocrystals. This defect configuration allows for thermal reactivation of electrons trapped in Dy 3+ -derived excited states, resulting in an increase in the nanocrystal emission intensity and an extension of the afterglow lifetime with temperature. These results are supported by kinetic Monte Carlo simulation based on the probability of different electron transfer processes. The results of this work demonstrate a pathway to extending afterglow emission in metal oxide nanocrystals and designing persistent nanophosphors.

Recent Progress in Inorganic Afterglow Materials: Mechanisms, Persistent Luminescent Properties, Modulating Methods, and Bioimaging Applications

“…As reported, assisting with suitable co‐dopants is one of the most efficient methods to optimize both the intensity and afterglow time of the afterglow. It is a universal method for all kinds of persistent phosphors, for instance, SrAl 2 O 4 :Eu 2+ ,Dy 3+ , [ 35 ] CaAl 2 O 4 :Eu 2+ ,Nd 3+ ,Gd 3+ , [ 41a,148 ] BaSiO 3 :Eu 2+ ,Nd 3+ ,Tm 3+ , [ 72 ] ZnGa 2 O 4 :Cr 3+ ,Gd 3+ , [ 95c ] Zn 2.94 Ga 1.96 Ge 2 O 10 :Cr 3+ ,Pr 3+ , [ 25b ] Zn 1.25 Ga 1.5 Ge 0.25 O 4 :Cr 3+ ,Yb 3+ ,Er 3+ , [ 149 ] MgGeO 3 :Mn 2+ ,Yb 3+ , [ 123 ] Mg 2 GeO 4 :Mn 2+ ,Yb 3+ , [ 121 ] CdSiO 3 :Bi 3+ ,Gd 3+ , [ 105a ] Y 2 O 2 S:Eu 3+ ,Mg 2+ ,Ti 4+ , [ 150 ] La 3 Ga 5 GeO 14 :Cr 3+ ,Zn 2+ , [ 151 ] ZnGa 2 O 4 :Cr 3+ ,Bi 3+ , [ 90a ] Ca 0.85 Zn 0.15 TiO 3 :Pr,B, [ 152 ] Ga 2 O 3 :Dy 3+ , [ 153 ] and Zn 2 GeO 4 :Mn,Li,K. [ 99b ]…”

“…In contrast, 580 nm ( 4 F 9/2 → 6 H 13/2 ) yellow emission originating from hypersensitive forced electric dipole transition will be impacted by the surrounding environment significantly. [ 68a–c,153,219 ] Thereby, dominant yellow luminescence will be produced by Dy 3+ in local site with low symmetry and without inversion symmetry, conversely, dominant blue luminescence will be generated. Chen et al reported the varied color of Dy 3+ in different hosts of Ca x MgSi 2 O 5+ x :Dy 3+ ( x = 1, 2, 3).…”

Development of Ca2+, Cr3+ Co‐Doped and Pr3+, Ca2+, Cr3+ Tri‐Doped β‐Ga2O3 Persistent Luminescence Nanoparticles with Enhanced Luminescence

“…Matsuzawa et al . first reported aluminates green PLNPs (SrAl 2 O 4 :Eu 3+ , Dy 3+ ) in 1996, [4] PLNPs attracted tremendous attention in various fields such as night lighting, national defense and military, optical storage, chemistry, materials, and biomedical sciences [5–11] . To date, various PLNPs matrixes were developed, e. g ., silicate, gallate, and Ga 2 O 3 .…”

“…Gallate matrix PLNPs attracted increasing interest in the presence of spinel structure, small bandgap energy difference, and stable chemical properties, [1] while they are still fundamentally plagued with poor fluorescence quantum efficiency, short persistent luminescence time, large particle size, poor water solubility, and low biocompatibility, [12] which greatly hinders their applications. Ga 2 O 3 matrix PLNPs have a wide band‐gap of 4.9 eV and contained native defects as the persistent luminescence activators that can be controlled via reaction conditions, and the dopants responsible for energy storage need to be externally introduced to design longer‐lasting nanophosphors based on Ga 2 O 3 [4,13–14] …”

One-step solvothermal synthesis and growth mechanism of well-crystallized β-Ga2O3 nanoparticles in isopropanol

“…With regard to its optical properties, β-Ga 2 O 3 is almost transparent, and β-Ga 2 O 3 nanoparticles have been demonstrated to exhibit photoluminescence upon doping. [8][9][10][11][12][13][14][15][16][17] In addition to these applications, β-Ga 2 O 3 has potential use in catalysis, 18,19 solar cells, 20 and gas sensors. 21 β-Ga 2 O 3 nanoparticles are also used as precursors in the synthesis of GaN nanoparticles via the nitration process.…”