Abstract
The dual-mode emission and multicolor outputs in the time domain from core-shell microcrystals are presented. The core-shell microcrystals, with NaYF4:Yb/Er as the core and NaYF4:Ce/Tb/Eu as the shell, were successfully fabricated by employing the hydrothermal method, which confines the activator ions into a separate region and minimizes the effect of surface quenching. The material is capable of both upconversion and downshifting emission, and their multicolor outputs in response to 980 nm near-infrared (NIR) excitation laser and 252 nm, and 395 nm ultraviolet (UV) excitation light have been investigated. Furthermore, the tunable color emissions by controlling the Tb3+-Eu3+ ratio in shells and the energy transfer of Ce3+→Tb3+→Eu3+ were discussed in details. In addition, color tuning of core-shell-structured microrods from green to red region in the time domain could be obtained by setting suitable delay time. Due to downshifting multicolor outputs (time-resolved and pump-wavelength-induced downshifting) coupled with the upconversion mode, the core-shell microrods can be potentially applied to displays and high-level security.
Highlights
Lanthanide (Ln3+)-doped luminescent materials with various compositions and properties have been well studied for the last few decades
The lanthanide-doped β-NaYF4 core-shell microcrystals that are composed of NaYF4:Yb/Er as TthheelcaonrtehaanndidNe-adYoFp4:eCde/βT-bN/EauYFas4 tchoeres-hsehlel lflomr dicuraolc-mryosdtaelsemthiasstiaorne(cUoCmapnodseDdSo) fwNeraeYfFa4b:rYicba/teEdr bays the cohreydarnodthNeramYaFl 4r:eCacet/ioTnb./TEhue NasaYthFe4:Ysbh/eElrl cfoorredmuiaclr-omrooddseseermveidssaios nse(eUdCmiacnrodroDdSs)afwteerraecifdabcrleicaantiendg by hydforrotthheermshael lrleagcrtoiwonth. , TrheesuNltianYgF4in:Ybth/eErfocromreatmioincroorfodcosrsee-srhveeldl aNsasYeFe4d:Ybm/Eicrr@oNroadYsF4a:Cftee/rTba/cEidu cleaninmgicfroorctrhyestsahlse.lTl ghreomwothrp, hreosluogltiiensgoifnmthateefroiarlms aarteiodnisopflcaoyreed-sbhyeSllENMaYimF4a:gYebs/(FEirg@uNrea1YaF–4d:C). eF/igTubr/eE1ua microcsrhyoswtaslst.hat Tthhee immaogrephofolsoegeidescryosftamls,atweritihalsa laernegtdhisapnldayaeddiabmyetSerEMof aibmoaugt e1s.20(Faignudr0e.211aμ–dm)
We have successfully designed an approach to achieve UC and DS luminescence simultaneously in core-shell microrods (NaYF4:Yb/Er@NaYF4:Ce/Tb/Eu). This approach helps confine the activators to different regions, overcoming the effect of the cross-relaxations between activators, and minimizing the effect of surface quenching without an outmost layer
Summary
Lanthanide (Ln3+)-doped luminescent materials with various compositions and properties have been well studied for the last few decades. Compared with traditional luminescent materials, such as quantum dots (QDs) and organic dyes, the lanthanide-doped nano- and micro-crystals show more superior optical features including narrow bands widths, stable energy levels, low toxicity and long lifetime [1,2]. These materials have attracted a great deal of attention owing to their magnetic and thermal properties. In order to decrease the affection of unnecessary luminescence quenching, these UC and DS Ln3+ ions dopants are usually doped into the core and shell layer, respectively. This design disturbs the interaction between these lanthanide ions, and is beneficial to overcome the luminescence quenching [1,13,22]
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