Photostimulated Persistent Luminescence Research Articles

Enhanced up-conversion persistent luminescence of Zn2GeO4:Mn phosphors by non-equivalent doping and sensitization of up-conversion nanocrystals

Up-conversion persistent luminescence (UCPL) nanoparticles have captured tremendous attention due to their unique optical operating performance such as the absence of auto-fluorescence and the charging capacity of near-infrared (NIR) light. However, the weak afterglow intensity as well as low duration limits their practical applications including multimode anti-counterfeiting and biological imaging, etc. Herein, typical green persistent luminescence (PersL) and photo-stimulated luminescence (PSL) of Zn2GeO4:Mn2+ phosphors were enhanced via non-equivalent Li+ co-doping, in which the preferred site selection of Mn2+ and Li + have been verified by using the first-principles theory. The possible luminescent enhancement mechanisms were proposed based on improving the oxygen vacancy density and promoting the formation of Mn4+ defect energy level in bandgap structure by non-equivalent doping of Li+. Interestingly, UCPL of Zn2GeO4:Mn2+,Li + can be achieved after charging of Vis to NIR light. It is worth noting that this UCPL can be further enhanced by the sensitization of NaYF4:Yb,Tm nanoparticles via simply mixing Zn2GeO4:Mn2+,Li+ and NaYF4:Yb,Tm under 980 laser stimulation. As a result, Zn2GeO4:Mn2+,Li+ phosphor exhibits the enhanced quintuple-mode luminescence including photoluminescence, PersL, PSL, photo-stimulated persistent luminescence and UCPL. In particular, the achieved NIR rechargeable UCPL hybrid phosphors exhibit enormous potential for higher order anti-counterfeiting and rewriteable data encryption and decryption applications.

Ultraviolet-C persistent luminescence from the Lu2SiO5:Pr3+ persistent phosphor for solar-blind optical tagging.

Visible and infrared persistent phosphors have gained considerable attention in recent years and are being widely used as glow-in-the-dark materials in dark environments. In contrast, the progress in persistent phosphors emitting at the other end of the spectrum, i.e., the shorter-wavelength ultraviolet-C (UVC; 200-280 nm), is rather slow. Here we report the design and synthesis of a well-performing Pr3+-doped UVC emissive persistent phosphor, Lu2SiO5:Pr3+, which exhibits intense UVC persistent luminescence peaking at 270 nm and a long persistence time of more than 12 h after excitation with a 254 nm UV lamp. Besides, the UVC persistent luminescence of a UV pre-irradiated sample can be repeatedly revived after repeated short-illumination with low-energy white light via a process called photostimulated persistent luminescence. Owing to the distinct spectral features of UVC light and the self-sustained luminescence properties, the UVC persistent luminescence of the Lu2SiO5:Pr3+ persistent phosphor can be clearly monitored and imaged using a corona camera in bright environments including direct sunlight and indoor light. The Lu2SiO5:Pr3+ persistent phosphor is expected to find promising applications in the covert optical tagging field.

Infrared-photostimulable and long-persistent ultraviolet-emitting phosphor LiLuGeO4:Bi3+,Yb3+ for biophotonic applications

A long-persistent ultraviolet-emitting phosphor LiLuGeO4:Bi3+,Yb3+ is synthesized. This phosphor exhibits simulated in vivo photostimulated persistent luminescence after a longtime decay by using in vitro NIR light penetrating biological tissue.

A NIR to NIR rechargeable long persistent luminescence phosphor Ca2Ga2GeO7:Yb3+,Tb3+

Near infrared to near infrared (NIR–NIR) photo-stimulated persistent luminescence (PSPL) has shown excellent potential in high-resolution bioimaging for deep tissues. However, the PSPL in NIR-Ⅱ region (900–1700 nm) is still lacking. In this work, Ca2Ga2GeO7:Yb3+,Tb3+ (CGGYT) phosphor with unique low-dimensional crystal structure was synthesized by high-temperature solid–state reaction. Thanks to the carriers transferring from deep traps to shallow ones induced by low energy light, the 978 nm PSPL originating from 2F5/2 to 2F7/2 transition of Yb3+ induced by multimode stimulating (980 nm or WLED) is successfully realized after pre-excited by UV lamp. The NIR PSPL of the specimen can be repeatedly stimulated after placed in dark for 12 h. Moreover, the results indicate that codoping with Tb3+ can significantly enhance the NIR-II PSPL owing to the quantum cutting persistent energy transfer (QC PET) from Tb3+ to Yb3+. Our study points to a new direction for the future development of multimode PSPL materials for bioimaging or multimode optical storage applications.

Long-lasting ultraviolet-A persistent luminescence and photostimulated persistent luminescence in Bi3+-doped LiScGeO4phosphor

A UVA emissive LiScGeO4:Bi3+persistent phosphor is developed, which exhibits single-band, long-lasting persistent luminescence and a photostimulated persistent luminescence capability.

Photostimulated near-infrared persistent luminescence Cr3+-doped Zn-Ga-Ge-O phosphor with high QE for optical information storage

Near-infrared (NIR) persistent luminescence (PersL) phosphors, which exhibit unique properties of high signal-to-noise ratio and wide excitation spectral region, have attracted more and more attention in the next-generation high-capacity storage system. In this paper, a multi-spectral excited NIR PersL phosphor, Zn1.25Ga1.5Ge0.25O4: Cr3+ (ZGG: Cr3+) which is developed by doping ZnGa2O4: Cr3+ with tetravalent Ge4+, has been successfully synthesized. Rietveld refinements show that Ge4+ ions enter into octahedral sites by substituting Ga3+ ions and the hetero-valence substitution enriches the charged defects. This PersL phosphor exhibits a zero-phonon lines emission of Cr3+ [2E→4A2g] with the maximum at 698 nm and the maximum values of IQE and EQE can reach to 60.3% and 22.4%, respectively. An intense photostimulated persistent luminescence (PSPL) can be repeatedly obtained by NIR laser stimulation in a period of more than 48 h (write-out) when the ZGG: Cr3+ phosphor illuminated by an ultraviolet-light (UV) (write-in). In addition, adopting thermoluminescence (TL) method, we studied the electron motion in traps and found a specific PersL mechanism which will be reported in this work. All these results demonstrate that the ZGG: Cr3+ phosphor has promising applications in optical information storage.

Cr3+-doped Mg4Ga4Ge3O16 near-infrared phosphor membrane for optical information storage and recording

A new near-infrared phosphor Mg4Ga4Ge3O16: Cr3+ with multi-photo-functionalities has been developed. Such phosphors can act as luminescent down-shifting materials converting UV and visible photons into NIR light (600–850 nm). UV irradiation induced strong NIR long persistent luminescence (LPL) can persist for more than 10 h. With the prolonged decay time, the extinguished NIR LPL can be rejuvenated by external photo stimulus including not only 980 nm light but also visible light. Such NIR photostimulated persistent luminescence (PSPL) presents separated write-in and read-out wavelength ranges. Meanwhile, photochromism (PC), that the material surface undergoes reversible change between white/pale green and ronbrown when triggered alternatively by UV and visible irradiation/heating, was also observed. Several recycle measurements demonstrate the robust fatigue resistance of PC property. Owning to the multi-photo-functionalities of Mg4Ga4Ge3O16: Cr3+, the fabrication of flexible phosphor membranes endows their application for optical information storage and repeatable optical recording. The electron motion in traps was studied by thermoluminescence (TL) and the color center formation was verified with electron spin resonance (ESR) spectra, based on which an energy level diagram was proposed for the illustration of the multifunctional mechanism. The revealing of multi-photo-functional mechanism and fabrication of flexible phosphor membranes may promote the development of a universal design principle for further study.

How to tune trap properties of persistent phosphor: Photostimulated persistent luminescence of NaLuGeO4:Bi3+,Cr3+ tailored by trap engineering

We take the NaLuGeO4:Bi3+,Cr3+ as a typical example to show an effective approach to tune the trap properties of persistent phosphor as needed. An empirical law concerning the trap engineering is summarized based on the experimental results and a large number of references. Guided by this law, the trap properties of this material are effectively tailored by Cr3+ codopants, and consequently the degradation of the infrared-to-ultraviolet persistent luminescence is greatly reduced. The calculations and a serial of thermoluminescence experiments have been conducted to verify the effect of the trap engineering. The infrared-to-ultraviolet persistent luminescence and trap properties are investigated in details. It demonstrates that the proposed empirical law concerning the trap engineering is indeed valid and the NaLuGeO4:Bi3+,Cr3+ material is potential for photodynamic therapy.

Near infrared photostimulated persistent luminescence and information storage of SrAl_2O_4:Eu^2+,Dy^3+ phosphor

The phosphor Sr0.97Al2O4:0.01Eu2+, 0.02Dy3+ was synthesized by a high temperature solid state reaction in a reducing atmosphere. After charging by ultraviolet radiation, the persistent luminescence decay was divided into different time ranges and well-fitted by a biexponential function, but the two lifetimes became longer with time of persistent luminescence decay. The fractional amplitude of the shorter lifetime increased with time, whereas that of the longer lifetime decreased. The change in lifetime has been associated with the emptying of a pseudo-continuum of trap states either from different traps or different levels of the same trap species. The investigation in photostimulated persistent luminescence indicated the sample could emit bright persistent luminescence again under infrared light excitation after the UV light-excited persistent luminescence had decayed completely. The NIR photostimulation exhibited a continuous broad band, with maximum at 760 nm, representing the emptying of filled traps into the conduction band. These results also infer that the traps are pseudo-continuous but the assignment of Dy2+ as the trapped species cannot be excluded. The read-in and write-out properties of the phosphor have been elucidated and these convey applications in information storage and retrieval.

New function of the Yb3+ ion as an efficient emitter of persistent luminescence in the short-wave infrared.

The trivalent ytterbium (Yb3+) ion has been extensively used as an emitter in short-wave infrared (SWIR) lasers, a sensitizer to activate other lanthanide ions for up-conversion luminescence, and a spectral converter in Ln3+-Yb3+ doubly doped quantum cutting phosphors. Here we report a new function of the Yb3+ ion—as an efficient emitting center for SWIR persistent luminescence. We have developed the first real SWIR persistent phosphor, MgGeO3:Yb3+, which exhibits very-long persistent luminescence at around 1000 nm for longer than 100 h. The MgGeO3:Yb3+ phosphor is spectrally transparent to visible/near-infrared light (~400–900 nm) and is a promising ultraviolet-to-SWIR spectral convertor. The MgGeO3:Yb3+ phosphor also exhibits a photostimulated persistent luminescence capability, where the SWIR persistent emission in an ultraviolet-light pre-irradiated sample can be rejuvenated by low-energy light (white or red light) stimulation. The MgGeO3:Yb3+ phosphor is expected to have promising applications in biomedical imaging, night-vision surveillance and photovoltaics.

Multifunctional near-infrared emitting Cr3+-doped Mg4Ga8Ge2O20particles with long persistent and photostimulated persistent luminescence, and photochromic properties

Multifunctional near-infrared emitting Cr3+-doped Mg4Ga8Ge2O20particles with long persistent and photostimulated persistent luminescence, and photochromic properties.

Photostimulated luminescence properties of Eu2+ -doped barium aluminate phosphor.

An intense green photostimulated luminescence in BaAl2 O4 :Eu(2+) phosphor was prepared. The thermoluminescence results indicate that there are at least three types of traps (T1 , T2 , T3 ) with different trap depths in BaAl2 O4 :Eu(2+) phosphor according to the bands located at 327, 361 and 555 K, respectively, which are closely associated with the phosphor's long persistent luminescence and photostimulated luminescence properties. In addition, as a novel optical read-out form, a photostimulated persistent luminescence signal can be repeatedly obtained in BaAl2 O4 :Eu(2+) phosphor. This shows that re-trapping of the electron released from a deep trap plays an important role in photostimulated persistent luminescence.

Photostimulable near-infrared persistent luminescent nanoprobes for ultrasensitive and longitudinal deep-tissue bio-imaging.

In vivo fluorescence imaging suffers from suboptimal signal-to-noise ratio and shallow detection depth, which is caused by the strong tissue autofluorescence under constant external excitation and the scattering and absorption of short-wavelength light in tissues. Here we address these limitations by using a novel type of optical nanoprobes, photostimulable LiGa5O8:Cr3+ near-infrared (NIR) persistent luminescence nanoparticles, which, with very-long-lasting NIR persistent luminescence and unique photo-stimulated persistent luminescence (PSPL) capability, allow optical imaging to be performed in an excitation-free and hence, autofluorescence-free manner. LiGa5O8:Cr3+ nanoparticles pre-charged by ultraviolet light can be repeatedly (>20 times) stimulated in vivo, even in deep tissues, by short-illumination (~15 seconds) with a white light-emitting-diode flashlight, giving rise to multiple NIR PSPL that expands the tracking window from several hours to more than 10 days. Our studies reveal promising potential of these nanoprobes in cell tracking and tumor targeting, exhibiting exceptional sensitivity and penetration that far exceed those afforded by conventional fluorescence imaging.

Photostimulated near-infrared persistent luminescence as a new optical read-out from Cr³⁺-doped LiGa₅O₈.

In conventional photostimulable storage phosphors, the optical information written by x-ray or ultraviolet irradiation is usually read out as a visible photostimulated luminescence (PSL) signal under the stimulation of a low-energy light with appropriate wavelength. Unlike the transient PSL, here we report a new optical read-out form, photostimulated persistent luminescence (PSPL) in the near-infrared (NIR), from a Cr3+-doped LiGa5O8 NIR persistent phosphor exhibiting a super-long NIR persistent luminescence of more than 1,000 h. An intense PSPL signal peaking at 716 nm can be repeatedly obtained in a period of more than 1,000 h when an ultraviolet-light (250–360 nm) pre-irradiated LiGa5O8:Cr3+ phosphor is repeatedly stimulated with a visible light or a NIR light. The LiGa5O8:Cr3+ phosphor has promising applications in optical information storage, night-vision surveillance, and in vivo bio-imaging.