Persistent Luminescence Decay Research Articles

Breaking the balance of chemical ratio in ZnAl2O4 to regulate activators and traps for multimode luminescence – A new strategy

As a common transition metal activator, the non-rare earth element Mn has good luminescent properties, so it has been widely concerned. It is reported that Mn2+ and Mn4+ can co-exist in the matrix, and the luminescence of Mn with different valence states is usually controlled by the co-doping of other ions. In this work, we controlled the green light emission of Mn2+, the red light emission of Mn4+, and the NIR emission of defects by breaking the balance of chemical ratio in ZnAl2O4:Mn to achieve multimode luminescence. The spinel-structured ZnAl2O4 phosphors with deficiency of zinc were synthesized by high-temperature solid-state reaction, which were characterized by a series of techniques, including XRD, DFT calculation, PLE/PL spectroscopy, TL, persistent luminescence decay curves, and temperature-dependent PL spectra analysis. The deficiency of zinc results in the appearance of zinc vacancy (VZn) and oxygen vacancy (VO), and the increased oxygen vacancy defects inhibit the self-reduction of Mn4+. Under the excitation of 325 nm and 426 nm ultraviolet light, the phosphor showed green emission at 510 nm, red emission at 678 nm, and near-infrared emission at 767 nm. Due to the increase of vacancy defects, the higher concentration of zinc deficiency leads to stronger emission of green light, red light, and near-infrared light. The phosphor exhibited different light signals at different excitation wavelengths, and the thermal stability of Mn2+ and Mn4+ luminescence is inconsistent. The above characteristics show that the multimode luminescent phosphor synthesized in this work has broad application prospects in the field of fluorescence anti-counterfeiting.

Incorporation of Mg2+/Si4+ in ZnGa2O4:Cr3+ to Generate Remarkably Improved Near-Infrared Persistent Luminescence

Near-infrared emitting nano-sized particles of ZnGa2−x(Mg/Si)xO4:Cr3+ (x = 0–0.15, termed as ZGMSO:Cr3+) with persistent luminescence were prepared by sol-gel processing followed by calcination. The samples were tested by XRD, TEM, STEM, SAED, Raman, XPS, UV-Vis-NIR, TL, PLE/PL spectroscopy, and persistent luminescence decay analysis. Equimolar incorporation of Mg2+ and Si4+ ions did not change the spindle structure of ZnGa2O4 seriously. Most Mg2+ ions are more likely to occupy the sites in octahedron, but Si4+ ions are more likely to occupy the sites in tetrahedron in priority. A broader bandgap, up shift of conduction band minimum, and more anti-defects were found at a higher Mg2+/Si4+ doping concentration. ZGMSO:Cr3+ outputs near-infrared emission with a dominated band at 694 nm (2E → 4A2 transition of Cr3+), which can last longer than 48 h after the stoppage of UV irradiation. Mg2+/Si4+ doping contributes to a better near-infrared persistent luminescence, and the strongest and the longest NIR afterglow was observed at x = 0.05, owing to that the x = 0.05 sample has the deepest defects. The synthesized nanoparticles of ZGMSO:Cr3+ not only output intense NIR afterglow but also can be recharged by the red light of LED several times, indicating that they are the potential nano probes for bio imaging in living animals.

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Optical Studies in Red/NIR Persistent Luminescent Cr-Doped Zinc Gallogermanate (ZGGO:Cr)

Zn1+xGa2−2xGexO4 (ZGGO:Cr)-persistent phosphor, with a molar fraction, x, of x = 0.1, doped with a 0.5% molar of chromium, was synthesised via solid-state reaction at 1350 °C for 36 h. X-ray diffraction measurements and Raman spectroscopy evidence a single crystalline phase corresponding to the cubic spinel structure. Room temperature (RT) photoluminescence (PL) and afterglow decay profiles were investigated using above and below bandgap excitation. In both cases, persistent PL was observed for almost 8 h, mainly originating from a Cr3+ defect, the so-called N2 optical centre. RT PL excitation and diffuse reflectance allow identification of the best pathways of Cr3+ red/NIR emission, as well as estimation of the ZGGO bandgap energy at 4.82 eV. An in-depth investigation of the observed luminescence at 15 K and temperature-dependent PL under site-selective excitation reveals the spectral complexity of the presence of several optically active Cr3+ centres in the ZGGO host that emit in almost the same spectral region. Furthermore, the temperature dependence of the R-lines’ intensity indicates the existence of thermal populating processes between the different optical centres. Such observations well account for a wide distribution of defect trap levels available for carrier capture/release, as measured by the persistent luminescence decay, from which the carriers are released preferentially to the N2 Cr3+-related optical centre.

Solvothermal synthesis and characterization of well-dispersed cerium-doped Y2SiO5 phosphor particles

Abstract Well-dispersed cerium-doped Y2SiO5 (Ce:YSO) phosphor particles with spherical morphology and good luminescence intensity have been achieved by a solvothermal method with ethanol and water as solvent media. X-ray diffraction, Fourier transform infrared spectroscopy, fluorescence spectrophotometry and transmission electron microscopy were employed to characterize the as-synthesized Ce:YSO precursor and powders. The results showed that pure-phase Ce:YSO powders with a mean particle size of about 162 nm were accurately available at 310°C and above. The fluorescence ability and persistent luminescence decay properties of the Ce:YSO powders were also studied, and the excellent fluorescence properties could be attributed to the homogeneous Ce:YSO particles obtained through the solvothermal method.

Structure and luminescence properties of Ce3+-activated BaLu2Al2Ga2SiO12 persistent phosphors for optical information storage

A novel BaLu2Al2Ga2SiO12:Ce3+ persistent phosphor was designed and synthesized through hetero-valence substituting Ba2+-Si4+ ion pair for Lu3+-Al3+ one in the Lu3Al3Ga2O12. XRD and Rietveld refinement results confirm the garnet typed crystal structure. SEM information shows that the constituent elements are uniformly distributed on the irregular particles. Under 360 or 430 nm excitation, the samples exhibit broad emission bands peaking at 510 nm. The luminescence intensity reaches to the maximum at 6 mol% Ce3+ doping content, and an internal quantum efficiency of 51.2% is achieved. The concentration quenching between Ce3+ ions is mainly originated from exchange interaction. Moreover, the phosphors exhibit bright cyan afterglow for minutes after removing the blue-light excitation source. The persistent luminescence decay process is studied by thermoluminescence spectra. The persistent luminescence mechanism and optical information writing and reading process are also discussed to explore the application in optical information storage.

Pressure-induced variation of persistent luminescence characteristics in Y3Al5-xGaxO12:Ce3+-M3+ (M = Yb, and Cr) phosphors: opposite trend of trap depth for 4f and 3d metal ions.

Changing the electronic structure of materials by pressure and the accompanying changes in optical properties have attracted scientific interest. We have reported that the energy position of the conduction band (CB) bottom and the crystal field splitting of the Ce3+:5d excited level in Y3Al5-xGaxO12:Ce3+ are changed by applying pressure, which results in the red shifting of the Ce3+:5d → 4f luminescence and the increase of the quenching temperature. We also reported dramatic improvement of the persistent luminescence performance by either Cr3+ or Yb3+ codoping into the Y3Al5-xGaxO12:Ce3+ phosphors. The different trap depths formed by Cr3+ and Yb3+ affect the initial persistent luminescence intensity and the persistent luminescence duration. In this study, the effect of pressure on the persistent luminescence performance was investigated. For the Y3AlGa4O12:Ce3+-Yb3+ phosphor, the slope of persistent luminescence decay curve becomes more gentle with increasing pressure, while for the Y3AlGa4O12:Ce3+-Cr3+ phosphor the slope becomes steeper. These results indicate that the trap depth of Yb3+ becomes deeper and that of Cr3+ becomes shallower with increasing pressure. Based on the pressure-dependence of the luminescence quenching and the trap depth change estimated from the decay slopes, the relative electronic energies of the CB bottom and the Yb2+ (4f14) or Cr2+ (3d4) levels are discussed. The CB bottom energy is increased relative to the ground 1S0 state of Yb2+ with increasing pressure, which results in deepening of the electron trap depth of the Yb2+ state. The opposite tendency of the Cr3+ codoped sample was described by a decreasing tendency of the energy gap between the CB bottom and the Cr2+:eg level, the relative energy level of which is increased by the increase of the crystal field with increasing pressure in the garnet host material, where the electron-trapping Cr2+ ions take the high spin state (t32ge1g) rather than the low-spin state (t42g).

Facile Synthesis of Mn4+-Activated Double Perovskite Germanate Phosphors with Near-Infrared Persistent Luminescence.

Tetravalent manganese doped phosphors are emerging as a new class of efficient near-infrared emitters for applications in a variety of areas, such as bioimaging and night-vision surveillance. Novel double perovskite-type La2MgGeO6:Mn4+ phosphors were successfully prepared using a microwave-assisted energy-saving solid state method. This simple technique involving the use of a microwave susceptor allows for a reduction of the preparation time compared to a conventional solid state reaction. The samples were investigated using powder X-ray diffraction, scanning electron microscopy, as well as energy-dispersive X-ray spectroscopy mapping, photoluminescence excitation/emission spectroscopy, persistent luminescence decay and temperature-dependent photoluminescence analysis. Substitution between isovalent Mn4+ and Ge4+ can be achieved without additional charge compensators in this germanate-based phosphor, which provides strong emission in the near-infrared spectral region, assigned to the characteristic transitions of tetravalent manganese ions. Additionally, the double perovskite-type germanate phosphor exhibits excellent luminescence thermal stability. Moreover, the spectroscopic properties, excitation wavelength-dependent and temperature-dependent persistent luminescence were studied. A series of thermoluminescence measurements were presented trying to give clear information on the charging process, afterglow behavior and the nature of the traps responsible for the persistent luminescence. The present investigation expands the range of available promising near-infrared emitting persistent phosphors for medical imaging.

Enhanced luminescence properties of ZnGa2O4:Cr3+ nanoparticles with an average crystallite size of 5 nm

ZnGa2O4:Cr3+ nanophosphors with an average crystallite size of 5 nm were prepared by a combustion method. We observed changes in the luminescence properties compared with the micro-crystalline system, such as a high brightness emission band at 696 nm and a decrease in the persistent luminescence decay time for the near-infrared emission. The system does not show a change in the band gap. The emission intensity for the broad band with near-infrared emission was very high under excitation with both UV and visible wavelengths.The system presents good stability in colloidal suspensions in water and phosphate-buffered saline, which were found to conserve the luminescence properties.The system is non-toxic and shows applications for in vivo optical imaging due to the rather high penetration depth of near-infrared radiation into human tissue. Its small crystallite size enables it to enter cells for bioimaging, exhibit good dispersion in a biological environment and resist photobleaching.

Positive effect of codoping Yb3+ on the super-long persistent luminescence of Cr3+-doped zinc aluminum germanate

A series of novel near-infrared (NIR) long persistent phosphors of Zn1.2Al1.6Ge0.2O4: Cr3+, Yb3+ was synthesized by a solid state method. The crystal structure of Zn1.2Al1.6Ge0.2O4 was identified. Yb3+ ions were effective codopants for improving the NIR persistent luminescence intensity even after 100 h of decay. The persistent luminescence decay curves and the thermo-luminescence spectra were analyzed. Results indicated that the increase in efficient electron trap concentration induced by doping Yb3+ ions was a major factor in the improvement of the NIR persistent luminescence. Moreover, short-wave infrared (SWIR = 900–1700 nm) emission of Yb3+ was be excited by UV and visible light through charge transfer transition of O2-–Yb3+ and energy transfer from Cr3+ to Yb3+, respectively.

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.

Trap depth and color variation of Ce3+-Cr3+ co-doped Gd3(Al,Ga)5O12 garnet persistent phosphors

Persistent luminescent properties in Ce3+-Cr3+ codoped Gd3Al5−xGaxO12 garnet (GAGG:Ce-Cr) solid solution have been investigated. The persistent luminescent color is shifted from orange to yellowish green with increasing Ga content because Ce3+: 5d level splitting becomes much weaker. The depth of electron trap introduced by Cr codoping was estimated from the intense thermoluminescence glow peak by the initial rise method. The trap depth decreases from 0.56 eV to 0.29 eV with increasing Ga content. The shift can be explained by downshift of bottom of conduction band. From the persistent luminescence decay curve measurement after ceasing 450 nm blue illumination, the samples with x = 2.5 exhibited the longest persistent luminescence for 405 min until the luminance becomes 2 mcd/m2 in GAGG:Ce-Cr phosphors.

Co-dopant influence on near-infrared luminescence properties of Zn2SnO4:Cr3+, Eu3+ ceramic discs

Bright near-infrared (NIR) luminescent ceramic discs of Zn2SnO4:Cr3+, Eu3+ were synthesized by a solid state method. The phase structure was checked by XRD. The photoluminescence and persistent luminescence decay properties of Cr3+, Eu3+-codoped samples were studied systematically. The photoluminescence and photoluminescence excitation spectra revealed that the NIR emission (centered at 800 nm) of Cr3+ was significantly enhanced after the incorporation of Eu3+ ions, which was attributed to the energy transfer from Eu3+ ions to Cr3+. Moreover, the incorporation of Eu3+ ions could effectively delay the decay rate and enhance the NIR persistent luminescence. The analysis of persistent decay curves and thermoluminescence spectra indicated that the Eu3+ ions acting as effective deep-trap centers contributed to improved Cr3+ NIR persistent luminescence.

Effect of RE3+ electronegativities on luminescence property of Ba5Si8O21:Eu2+ persistent phosphor

A series of Ba5Si8O21:0.02Eu2+,0.09RE3+ persistent phosphors were synthesized by the solid-state reaction method. The measurement results of photoluminescence (PL), phosphorescence and thermoluminescence (TL) were analysed and discussed. The XRD results showed that samples codoped with different RE3+ were Ba5Si8O21 single pure phase. Under the excitation, all samples exhibited a broad Eu2+ characteristic emission, and the La3+ co-doped sample emitted the brightest photoluminescence even though its persistent luminescence property was the worst because of the weakest electronegativity. However, Nd3+ electronegativity was suitable, thus after activation, the Ba5Si8O21:Eu2+,Nd3+ sample had the best persistent luminescence performance with the highest phosphorescence intensity and the persistent luminescence decay time beyond 8 h. The Nd3+ co-doped sample also had the largest thermoluminescence integral area which proved effectively it had longer persistent luminescence time. The luminescence mechanism was also proposed to study the photoluminescence and persistent luminescence process. These results showed that RE3+ electronegativities were distinctly important for persistent phosphors and choosing suitable electronegativity codopant was conducive to enhancing the phosphorescent performance.

Preparation and characterization of a long persistent phosphor Na_2Ca_3Si_2O_8:Ce^3+

A novel host lattice Na2Ca3Si2O8 was used for synthesizing long persistent phosphors for the first time. A blue-emitting long persistent phosphor was prepared successfully via a traditional high temperature solid-state reaction method. The phase structure was checked by XRD. The photoluminescence and persistent luminescence decay properties of Ce3+-doped samples were studied systematically. The defects acting as traps were investigated by thermoluminescence. It demonstrated that the doping Ce3+ ions into the Na2Ca3Si2O8 host not only largely enriched the intrinsic traps but also introduced abundant new extrinsic traps which play a determining role in the generation of persistent luminescence. The origin of the persistent luminescence was analyzed and a related mechanism was systematically discussed based on a schematic diagram as well.

A predictive mechanoluminescence transduction model for thin-film SrAl2O4:Eu2+, Dy3+ (SAOED) stress sensor

This paper proposes a phenomenological stress-optics transduction model for predicting mechanoluminescence (ML) light intensity from a thin-film ML coating sensor subjected to in-plane stresses. Recent findings on the considerable effects of persistent luminescence (PL) decay on ML phenomena (Rahimi MR, Yun GJ, Doll GL, Choi JS. Opt Lett 2013;38:193235) have motivated the incorporation of critical factors (i.e. strain rate, stress-free PL decay time interval, photoexcitation time, instantaneous PL decay rate, etc.) into a predictive ML transduction model. In the proposed model, the total ML+PL light emission is subdivided into a net ML emission, stress-free PL decay, and additional stress-induced PL decay. These are separately modeled and combined on the basis of interaction of the ML phenomena with PL decay and the effects of strain rates and PL decay time intervals. Predictions by the proposed model were found to agree well with experimental results. The relative total ML+PL light intensity was also proven to be linearly proportional to the mechanical strain energy. The proposed predictive model can be broadly used in the design of ML sensing film and in applications for the calibration process.

Persistent luminescence and photocatalytic properties of Ga2O3:Cr3+,Zn2+ phosphors

Ga2O3:Cr3+0.01, Zn2+0.005 and Ga2O3:Cr3+0.01 phosphors were synthesized by the high temperature solid state reaction. The emission and excitation spectra, persistent luminescence decay curve, thermoluminescence curve and photocatalytic properties were measured. The emission and excitation spectra indicate that the Zn2+ doping has no effect on photoluminescent properties of Ga2O3:Cr3+0.01. The red persistent luminescence of Ga2O3:Cr3+0.01, Zn2+0.005 could be observed for 20min by naked eye. The thermoluminescence (TL) curve shows that a suitable trap was introduced into the Ga2O3:Cr3+ host by Zn2+ doping. The photocatalytic activity toward rhodamineB (RhB) was obtained to evaluate photocatalytic properties by Zn2+ doping. The results indicate that the Zn2+ doping could improve the photocatalytic properties of Ga2O3:Cr3+0.01 phosphors. It was considered that the new traps play an important role for trapping the electrons or holes to decrease the combination of the electrons and holes producing by the light irradiation and increase the photocatalytic activity.

Effects of persistent luminescence decay on mechanoluminescence phenomena of SrAl_2O_4:Eu^2+, Dy^3+ materials

This Letter reveals for the first time, to the best of our knowledge, the effects of stress-free persistent luminescence (PL) decay on the mechanoluminescence (ML) phenomena and the effects of stresses and strain rates on the PL decay of SrAl(2)O(4):Eu(2+), Dy(3+) (SAOED) materials. Previous research on ML phenomena in this material has focused on the effects of strain rates and stress variations on ML light intensity. However, experimental evidence provided herein shows that the ML light emission is also related to the PL decay time elapsed until the onset of stressing and the PL decay rate is dependent on the stress, strain rate, and the stress-free PL decay time interval. For quantitative stress measurements using SAOED materials, understanding of ML light sensitivity and its dependence on critical factors (strain rate, stress-free PL decay time interval, photoexcitation time, instantaneous PL decay rate, etc.) is crucially important. This Letter provides new and important perspectives that are essential for developing predictive models and/or calibration procedures for ML stress sensors.

Persistent luminescence of Eu 2+ and Dy 3+ doped barium aluminate (BaAl 2O 4:Eu 2+,Dy 3+) materials

Polycrystalline Eu 2+ and Dy 3+ doped barium aluminate materials, BaAl 2O 4:Eu 2+,Dy 3+, were prepared with solid state reactions at temperatures between 700 and 1500 °C. The influence of the thermal treatments on the stability, homogeneity and structure as well as to the UV-excited and persistent luminescence of the materials was investigated by X-ray powder diffraction, SEM imaging and infrared spectroscopies as well as by steady state luminescence spectroscopy and persistent luminescence decay curves, respectively. The IR spectra of the materials prepared at 250, 700, and 1500 °C follow the formation of BaAl 2O 4 composition whereas the X-ray powder diffraction of compounds revealed how the hexagonal structure was obtained. The morphology of the materials at high temperatures indicated important aggregation due to sintering. The luminescence decay of the quite narrow Eu 2+ band at ca. 500 nm shows the presence of persistent luminescence after UV irradiation. The dopant (Eu 2+) and co-dopant (Dy 3+) concentrations affect the crystallinity and luminescence properties of the materials.