Zitao Chen

Single-band red upconversion luminescence of Yb3+–Er3+via nonequivalent substitution in perovskite KMgF3 nanocrystals

Single-band red upconversion (UC) emission of Er3+ has been successfully achieved in Yb3+/Er3+ codoped KMgF3 nanocrystals via a nonequivalent substitution strategy, in which lanthanide ions probably aggregate, as evidenced by density functional theory calculations and upconversion dynamic processes. The aggregation of Yb3+/Er3+ would cause large cross-relaxation probabilities among the lanthanide ions when photo-excited, resulting in the disappearance of the green emission and the population of the red emitting level of Er3+. Interestingly, the single-band feature is independent of the dopant concentration and pump power. The possible UC mechanism is discussed in detail according to nanocrystal morphology, ion radii, lattice parameters and decay lifetime studies of the Yb3+–Er3+ doped analogous compounds (KMgF3, KZnF3 and KCdF3). It could be concluded that Yb3+/Er3+ ions tend to aggregate in KMgF3, resulting in the largest ratio of red to green UC emission. This research may give a perspective toward tuning the UC emission of lanthanide ions.

Multifunctionalities of near-infrared upconversion luminescence, optical temperature sensing and long persistent luminescence in La3Ga5GeO14:Cr3+,Yb3+,Er3+ and their potential coupling

The multifunctionalities of La3Ga5GeO14:Cr3+,Yb3+,Er3+ (LGG:Cr3+,Yb3+,Er3+) with respective functions of near-infrared (NIR) upconversion (UC) luminescence, optical temperature sensing (OTS) and long persistent luminescence (LPL) were carried out and investigated in detail, which makes the materials attractive for bioapplications. The NIR UC luminescence at ∼830 nm with deep penetration in tissues is ascribed to the 4T2 → 4A2 transition of Cr3+. The OTS function based on the intensity ratio variation of 2H11/2 → 4I15/2 to 4S3/2 → 4I15/2 transitions of Er3+ ion detected that the thermal effects of the UC material caused by the laser irradiation ranges from 307 to 332 K for pumping power of 60 to 86 mW mm−2. It also showed LPL of Cr3+ with a defect trap depth of ∼0.77 eV below the conduction band, benefiting excitation-free and noise-free imaging in tissues. Additionally, anomalous temperature dependant UC emission behaviours of Cr3+ and Er3+ in this material were also characterized and discussed, which can be understood by the configurational coordinate (CC) model and the complex forward and backward energy transfer processes among the dopants, respectively. The potential coupling of these functions was further discussed, such as UC induced NIR LPL, which would repetitively restrengthen the fading LPL signals and alert the operators to thermal damage of the biosystems by the NIR laser in the tissue imaging.

Tunable white upconversion luminescence from Yb 3+ -Tm 3+ -Mn 2+ tri-doped perovskite nanocrystals

Tunable broadband white upconversion (UC) luminescence has been demonstrated in Yb3+/Tm3+/Mn2+ tri-doped KZnF3 nanocrystals from the excitation of a 976 nm laser diode (LD). The white light is composed of three sharp band peaks at 480, 650 and 700 nm, originating from the UC emissions of Tm3+ ions, and one broad band centered at 585 nm, originating from exchange-coupled Yb3+–Mn2+ dimers. The effects of the concentration, pump power and temperature on the UC luminescence properties of KZnF3:Yb3+,Tm3+,Mn2+ nanocrystals have been investigated. By changing the Mn2+/Tm3+ content ratio, various colors of the UC luminescence can be easily obtained in KZnF3:Yb3+,Tm3+,Mn2+ nanocrystals, which gives these nanocrystals potential applications in the fields of lighting, displays and lasers.

Mesoporous nanoparticles Gd2O3@mSiO2/ZnGa2O4:Cr3+,Bi3+ as multifunctional probes for bioimaging

Red/near infrared (NIR) persistent luminescent nanoparticles (PLNPs) hold great potential as a new generation of probes for the detection and imaging of biomolecules. Based upon the consideration that a single nanoprobe could serve multiple purposes, the development of a multimodal nanoprobe that combined the properties of rechargeable persistent emitting luminescence, magnetic resonance imaging (MRI) and drug delivery has attracted our attention as a promising prospect in the field of nanotechnology directed toward biomedical applications. Herein, Gd2O3@mSiO2/ZnGa2O4:Cr3+,Bi3+ (ZGOCB) mesoporous nanoparticles that exhibit enhancement of red (∼695 nm) persistent luminescence (∼18 d) properties were synthesized by using mesoporous silica nanospheres both as morphology-controlling templates and vessels. Being composed of hybrid shell/core architecture and through surface functionalization, Gd2O3@mSiO2/ZGOCB mesoporous nanoparticles possess the capacity for in vivo and in situ real-time monitoring, targeting tumors and drug delivery. Simultaneously, Gd2O3@mSiO2/ZGOCB exhibits a prominent longitudinal relaxivity, indicating that these nanoparticles could also be used as magnetic resonance imaging agents. We believe that this rechargeable red persistent luminescence and MRI-based core/shell structure of the multimodal nanoprobe offers a promising nano-platform for both diagnostics and therapeutics of reactive species in living cells or in vivo.

Near-infrared wavelength-dependent nonlinear transmittance tailoring in glass ceramics containing Er3+:LaF3 nanocrystals

Nonlinear optical (NLO) effects originating from materials doped with rare-earth ions possess colossal potential for application in all-optical switches. However, among previous studies, Er3+ ion-doped glass ceramics (GCs) with remarkable NLO features have been investigated with respect to optical modulation applications by tailoring their nonlinear transmittance upon excitation at various near-infrared (NIR) wavelengths, which might prove to be a simple way of achieving “on–off” optical modulation in future all-optical switches. Here, we present the first observation of tailorable nonlinear transmittance in germanate oxyfluoride GCs containing Er3+:LaF3 nanocrystals, manipulated by excitation at 808, 980, and 1550 nm, which is consistent with the results from theoretical calculations and simulations. Furthermore, we conduct experimental investigation and analysis related to energy level transitions and dynamical evolution, indicating that these intriguing NLO features can be attributed to the differentiation between excited state absorption accompanied by up-conversion luminescence and stimulated emission processes during excitation at discrepant NIR wavelengths. Importantly, bidirectional optical switching for the “on–off” toggle effect has been successfully demonstrated by selectively tailoring the nonlinear transmittance of the single Er3+-doped GCs. This tailorable NLO behavior of Er3+-doped GCs, which is dependent on excitation at different NIR wavelengths, might provide a versatile strategy for the development of next-generation bidirectional all-optical switches.

Tailoring the upconversion of ABF3:Yb3+/Er3+ through Mn2+ doping

Successful upconversion (UC) tuning from multi-bands to one single red band from Er3+ ions was realized in cubic perovskite ABF3:Yb3+/Er3+ (A = K, Cs; B = Zn, Cd) through Mn2+ doping. Based on UC emission spectra and decay kinetics of KZnF3:Yb3+/Er3+ with different Mn2+ contents, a bidirectional energy transfer process between Mn2+ and Er3+ ions was confirmed to explain the UC tuning mechanism. More importantly, we studied the influence of the Mn2+ energy level position on the UC properties for Er3+ in ABF3 hosts. Interestingly, great enhancement of green UC emissions was observed for Er3+ ions in KCdF3 and CsCdF3 hosts upon Mn2+ doping. Comparison of UC emissions and lifetimes of Er3+ ions in the three materials was carried out to probe the different UC processes in ABF3 (A = K, Cs; B = Zn, Cd) hosts. The different energy transfer mechanism between Mn2+ and Er3+, which is affected by the Mn2+ energy level position, was proposed to explain the UC difference in the three matrices. This research convincingly confirmed the occurrence of energy transfer between Er3+ and Mn2+ ions and provided deep insights into the importance of the Mn2+ energy level position in tuning the UC properties of Er3+ in diverse hosts, while allowing us to better control the UC properties through Mn2+ doping.

Exchange coupled Mn-Mn pair: An approach for super-broadband 1380 nm emission in α-MnS

Super-broadband near-infrared (NIR) emission centered at 1380 nm with a full width at half maximum of 161 nm and a decay lifetime of 241 μs has been demonstrated in α-MnS. We find that the NIR emission originates from exchange coupled Mn-Mn pairs in α-MnS based on the detail analysis of photoluminescence excitation spectra, transient spectra, temperature dependent photoluminescence spectra as well as the crystal structure of α-MnS. Mechanism of exchange interaction between nearest-neighbor Mn2+ ions is discussed in detail. The finding offers the possibilities of designing NIR emitting source for various photonic applications.

Tunable multiple emissions in manganese-concentrated sulfide through simultaneous tailoring of Mn-site coordination and Mn-Mn pair geometry

In contrast to generally single-band visible emission feature from Mn2+, simultaneous visible (VIS) and near-infrared (NIR) multiple emissions are demonstrated in Mn2+ concentrated sulfide (MnS) by only involving a single crystallographic site. Upon varying the Mn2+-site coordination and/or Mn-Mn pairs geometry in different structural MnS, the multiple emissions from divalent manganese can be easily tuned from 575 to 720 nm (VIS) or from 880 to 900 or 1380 nm (NIR), respectively. The excitation spectroscopy and the luminescent decay, together with crystal structural analyses, are employed to investigate the electronic transition and the excited state dynamics of these Mn2+ concentrated systems. It is found that the VIS and NIR emissions can be ascribed to the isolated Mn2+ ion and exchange coupled Mn-Mn pair center, respectively. The effect of crystal field and bridging geometry, as well as temperature on the exchange coupled Mn2+ pairs NIR emissive center, is also investigated in detail. This work not on...