Regular ArticleIntermediate excited state suppression and upconversion enhancement of Er3+ ions by carbon-doping boosting photocarrier separation in bismuth oxychloride nanosheets
Graphical abstract
The spontaneous IEF inside the BiOCl was improved significantly by C doping, which can suppress the recombination of photoelectron-hole pairs. The stronger IEF inhibits the recombination rate of electrons on the intermediate state 4I13/2 of Er3+ ions, which promotes the energy reabsorption transition to the upper energy levels to enhance the visible UC emission.
Introduction
In recent years, upconversion luminescence (UCL) of trivalent rare-earth ions (RE3+) doped nanophosphors has drawn considerable interest, due to their potential applications in lasers, [1], [2] solar cells, [3], [4], [5] biological fluorescence imaging and near infrared (IR) detection, [6], [7] IR quantum counters, [8] and display technologies [9]. However, the insufficient luminescence intensity still constitutes the main limitation for practical applications of nanosized UC materials because of more defects and impurities [10]. Up to now, various methods have been attempted to improve UC luminescence efficiency, such as modulating energy transfer, [11], [12] broadening the absorption region [13] and manipulating host lattice [14], [15].
As for the UC process, the nonradiative relaxation of RE3+ ions place restrictions on UCL efficiency for nanomaterials [10]. Traditionally, selecting suitable host of low phonon energy and fabricating core-shell structure have been used to eliminate the nonradiative relaxation of RE3+ in the UC nanophosphors [16], [17]. Conversely, Yang reported a different strategy for the enhancement of the UC emissions. They showed that using the photonic crystals band gap to suppress the spontaneous emission from intermediate excited state of RE3+ ions, where the electrons occupation possibility of the excited energy level could be improved, is effective in the enhancement of visible UC emissions similarly [18]. Although the complexity of structural design and the wavelength limitation of photonic crystals may restrict the practice applications, it brings a good inspiration that we can design the inherent structure or component for host materials to suppress the spontaneous relaxation of electrons at intermediate excited state, thus promoting the energy reabsorption to enhance the UC emissions.
Over the last few years, the rapid increase in graphene has led to the development of an active research field focusing on two-dimensional (2D) layered materials. It is worth noting that these materials have higher carrier mobility and separation efficiency of electron-hole pairs due to their wide range of anisotropic properties [19], [20], [21]. Especially, illustrated by the example of Bi-based polarized semiconductors, such as BiOX (X = F, Cl, Br or I), BiOIO3, Bi2O2[BO2(OH)], Bi4NbO8Cl and Bi3O4Cl, a layered semiconductor having spontaneous electric polarization shows important applications in electronic information technology, which have been reported as efficient photocatalysts in organic pollutants degradation, H2 evolution and CO2 photoreduction [22], [23], [24], [25], [26], [27]. These materials have mostly been favored as the photocatalysis since they present the excellent wide-band photocatalysis performance over their band gap [28], [29]. The phenomena show such a fact that, in these layered semiconductors, the photoelectrons generated from the intermediate levels, which is caused by impurities, defects or other factors, might be separated and utilized efficiently to improve the photocatalytic ability [30], [31], [32]. One important reason is that they all possess the spontaneous inter electric field (IEF) as efficient inhibition of photoelectron-hole pair recombination [33], [34], [35].
Inspired by the inter crisscross application of the knowledge in different field, we predicate that when the f-f energy level of RE3+ dopants act as the impurity levels in the layered host, the IEF may decrease the recombination rate of intermediate excited state electrons similarly. As a result, when the IEF is high enough or is enhanced to an enough level, it may offer the possibility to inhabit the spontaneous relaxation rate of intermediate excited state electrons of RE3+ ions and prolong its decay time. This will increase the probability of transitioning to the higher energy level and improve the UC emission consequently.
To confirm our idea, we prepared C-Er3+ co-doped BiOCl single-crystalline nanosheets and investigated the influence of IEF on the UC emission properties via heterovalent doping of carbon. The reason that we chose this strategy is that the separation of photoelectrons inside the BiOCl nanocrystals can be tailored via C impurity doping; [36] meanwhile, it has been found that the polarization enhancement of other layered semiconductors via heterovalent doping has the ability to promote the separation of charge carriers [7]. On the other hand, we recently observed that the lightly-doped C into the BiOCl nanosheets will quench the downshifting emission intensity of Eu3+ ions, but can modify the emission behaviors of electric dipole transition of Eu3+ ion dopants significantly via photoferroelectric effect, as the C doping enhance the IEF [37]. In this work, in a much higher doping level, we show that due to boosting the spontaneous IEF more significantly, the C dopants not only can increase the carrier effective mass along [0 0 1] direction, but also inhibit the recombination rate of photoelectrons and holes in the BiOCl nanosheets. As a result, the decay time of the intermediate state of Er3+ ions (4I13/2 level) is prolonged significantly by more efficient hole separation and transfer inside nanosheet host, thus promoting the energy reabsorption transition to upper energy levels and the visible UC emission greatly.
Section snippets
Synthesis details
Samples of BiOCl:3%Er/xC (x = 0, 1, 2, 3 mmol) were prepared via a hydrothermal processing and a subsequent thermal treatment with glucose as the carbon dopants source, [36] which were called as 0C, 1C, 2C, 3C, respectively, specific synthesis details refer to supplementary information.
The details of characterizations and theoretical calculations for the sample are shown in the Electronic supplementary information.
Phase identification of C doped BiOCl nanosheet
Fig. 1 shows the X-ray diffraction (XRD) patterns of the BiOCl:3%Er/x C (x = 0, 1, 2, 3 mmol) nanocrystals. The XRD patterns of the prepared samples can be clearly indexed to the tetragonal BiOCl phase (JCPDS: 06-0249). The intense and sharp diffraction peaks show that the as-synthesized product was well-crystallized and no other diffraction peaks of carbon atoms is detected, indicating the reliability and the feasibility of this C doping strategy.
The surface element compositions and chemical
Discussion
To confirm the reason that C doping prolong the intermediate excited state of Er3+ ions, namely the enhanced IEF rather than the conventional lattice modification effect, the UC enhancement mechanism caused by the lattice modification was discussed as a distinction. In briefly, according to the Judd-Ofelt (J-O) theory, as the symmetry of the crystal sites around the RE dopants is changed by heterovalent doping, the intensity of UCL can be calculated by the following steady-state Eq. [15]:
Conclusions
In summary, via a hydrothermal processing and a subsequent thermal treatment, the influence of heterovalent C doping on the UC luminescence properties of Er3+ doped BiOCl nanosheets were investigated in detail. The theoretical calculations and SPV tests provide evidences that the spontaneous IEF at the direction of (0 0 1) of BiOCl nanosheets was improved significantly with doping C, suppressing the recombination of photoelectron-hole pairs more efficiently. Under the stronger IEF, the separated
CRediT authorship contribution statement
Jiajun Han: Writing - original draft. Taizhong Xiao: . Jiajing Wang: Formal analysis. Tong Liu: Data curation. YongJin Li: Formal analysis, Software. : . Yuehong Peng: Formal analysis, Software. Zhaoyi Yin: Conceptualization. Jianbei Qiu: Supervision, Validation. Zhengwen Yang: Supervision, Validation. Zhiguo Song: Funding acquisition, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work is supported by the National Natural Science Foundation of China (No. 11874186) and Foundation of Yunnan Province 2019HC016.
References (48)
- et al.
Two distinct simultaneous NIR looping behaviours of Er3+ singly doped BiOBr: The underlying nature of the Er3+ ion photon avalanche emission induced by a layered structure
J. Alloy. Compd.
(2019) - et al.
Enhancement of upconversion luminescence of Y2O3:Er3+ nanocrystals by codoping Li+-Zn2+
J. Alloy. Compd.
(2011) - et al.
Modification of the upconversion spontaneous emission in photonic crystals
Mater. Chem. Phys.
(2012) - et al.
Internal polar field enhanced H2 evolution of BiOIO3 nanoplates
Int. J. Hydrogen Energy
(2016) - et al.
Synthesis of olive-green few-layered BiOI for efficient photoreduction of CO2 into solar fuels under visible/near-infrared light
Sol. Energy Mater. Sol. Cells
(2016) - et al.
Highly enhanced visible light photocatalysis and in situ FT-IR studies on Bi metal@defective BiOCl hierarchical microspheres
Appl. Catal. B
(2018) - et al.
Unusual photoluminescence regulation of single-crystalline BiOCl:Eu3+ nanosheet by C-heterovalent doping: The evidence of photoferroelectric effect on the transitions of the RE3+ optical activator
Ceram. Int.
(2020) - et al.
Selective transport of electron and hole among 0 0 1 and 1 1 0 facets of BiOCl for pure water splitting
Appl. Catal. B
(2015) - et al.
DFT+U predictions: The effect of oxygen vacancy on the structural, electronic and photocatalytic properties of Mn-doped BiOCl
Comput. Mater. Sci.
(2013) - et al.
Oxygen vacancy induced superior visible-light-driven photo-catalytic performance in the BiOCl homojunction
Mater. Chem. Front.
(2020)
Novel g-C3N4 nanosheets/CDs/BiOCl photocatalysts with exceptional activity under visible light
J. Am. Ceram. Soc.
Upconverter solar cells: materials and applications
Energy Environ. Sci.
Enhancing solar cell efficiency: the search for luminescent materials as spectral converters
Chem. Soc. Rev.
Downconversion for solar cells in NaYF4:Er Yb
J. Appl. Phys.
Rare-earth nanoparticles with enhanced upconversion emission and suppressed rare-Earth-ion leakage
Chemistry
Energy transfer from quantum dots to metal-organic frameworks for enhanced light harvesting
J Am Chem Soc
Review of the properties of up-conversion phosphors for new emissive displays
J. Disp. Technol.
Emergence of photoluminescence enhancement of Eu3+ doped BiOCl single-crystalline nanosheets at reduced vertical dimensions
Nanoscale
Broadband Cr3+-sensitized upconversion luminescence in La3Ga5GeO14: Cr3+, Yb3+, Er3+
Opt. Mater. Express
Nd3+-sensitized upconversion nanophosphors: efficient in vivo bioimaging probes with minimized heating effect
ACS Nano
Broadband dye-sensitized upconversion of near-infrared light
Nat. Photonics
High multi-photon visible upconversion emissions of Er3+ singly doped BiOCl microcrystals: A photon avalanche of Er3+ induced by 980 nm excitation
Appl. Phys. Lett.
Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals
Adv. Mater.
Tuning upconversion through energy migration in core-shell nanoparticles
Nat Mater
Cited by (6)
In-site interface growth of bismuth-based hydrothermal carbon using collagen fiber for selective removal of iodide ion from wastewater
2023, Colloids and Surfaces A: Physicochemical and Engineering AspectsEnhanced upconversion luminescence in layered Bi<inf>2</inf>GdO<inf>4</inf>Cl:Yb<sup>3+</sup>/Er<sup>3+</sup> by reducing OVs and its application in photocatalysis
2022, Journal of LuminescenceCitation Excerpt :However, until now, the relatively low UC luminescent efficiency remains a major bottleneck for the practical application of the bismuth oxyhalide. Over the last few years, various approaches have been devoted to improving the UC luminescent efficiency of bismuth oxyhalide, including crystal field modulation, energy transfer, structural design, etc [10–14]. For example, Li et al. synthesized 3D flowerlike BiOBr:Yb3+/Er3+ hierarchical architectures, which exhibited significantly enhanced UC emission compared with 2D nanosheets [10].
Boosting photodegradation of dye solutions based on Eu<sup>3+</sup> doping in Bismuth-layered oxyhalogenide semiconductor NaBi<inf>3</inf>O<inf>4</inf>Cl<inf>1.5</inf>Br<inf>0.5</inf>
2021, Applied Surface ScienceCitation Excerpt :The framework contains the unique [Bi2O2]2+ slabs alternatively separated by M−O polyhedra (M: catiion) or halide (F, Cl, Br, I) layers.[17] The strong polarization effect can be produced due to intralayer interactions, which is advantageous for dielectrics, ferroelectrics, and photocatalysis [18–22]. Especially, the effective separation of photo-produced hole-electron charge in bismuth layered oxyhalogenides can greatly improve the photocatalysis for photodegradation of pollutants and water-splitting [23].
Vertical GaN Schottky Barrier Diode With Record High Figure of Merit (1.1 GW/cm<sup>2</sup>) Fully Grown by Hydride Vapor Phase Epitaxy
2023, IEEE Transactions on Electron DevicesEnergy Migration Control of Multimodal Emissions in an Er<sup>3+</sup>-Doped Nanostructure for Information Encryption and Deep-Learning Decoding
2021, Angewandte Chemie - International Edition
- 1
These authors made equal contribution to this work.