Shaochun Han

Design, synthesis and characterization of a novel yellow long-persistent phosphor: Ca2BO3Cl:Eu2+,Dy3+

A novel yellow emitting long-persistent phosphor Ca2BO3Cl:Eu2+,Dy3+ is developed. The incorporation of Dy3+ ions, which act as trap centers, largely extends the thermoluminescence characteristics and evidently enhances the persistent luminescence behavior of the phosphor. Both fluorescence and phosphorescence spectra of Ca2BO3Cl:Eu2+,Dy3+ reveal only one asymmetric broad emission band located at 580 nm, ascribed to the 5d–4f transitions of Eu2+ ions in two different sites. With the optimum doping concentration and sufficient excitation with UV light, the afterglow of samples can persist over 48 h above the recognizable intensity level (≥0.32 mcd m−2), a phenomenon that is infrequent and excellent. Furthermore, Ca2BO3Cl possesses an indirect bandgap of about 5.1 eV. Detailed processes and possible mechanism are studied and discussed.

A new type of color tunable composite phosphor Y2SiO5:Ce/Y3Al5O12:Ce for field emission displays

A simple but effective strategy was introduced to realize color tunability of a composite phosphor Y2SiO5:Ce/Y3Al5O12:Ce (YSO:Ce/YAG:Ce). The main idea was to use the cathodoluminescence of the YSO:Ce phosphor to additionally pump the photoluminescence of the YAG:Ce phosphor based on radiative energy transfer. Morphology as well as the cathodoluminescence properties of the YSO:Ce/YAG:Ce phosphors were investigated in detail. According to radiative energy transfer, an intense yellow emission with excellent cathodoluminescence properties can be obtained from YSO:Ce/YAG:Ce phosphors under low voltage electron beam excitation. Moreover, the emission color of the composite phosphors can be tuned from yellow to blue through adjusting the YSO:Ce content. The mechanism for the enhanced yellow emission and the color tunability were also discussed. It was experimentally proved that the color gamut and display hue could be greatly enriched and enhanced when employing the YSO:Ce/YAG:Ce composite phosphor as an additional phosphor for the typical tricolor FED phosphors.

Photo-/cathodoluminescence and energy transfer properties of novel Ce3+ singly doped and Ce3+/Tb3+ codoped NaBaScSi2O7 phosphors

A series of novel Ce3+ singly doped and Ce3+/Tb3+ codoped color-tunable NaBaScSi2O7 phosphors were synthesized via the solid state method. The morphology, UV-vis reflectance, photoluminescence emission and excitation spectra, the lifetime and the thermal quenching properties were investigated in detail. NaBaScSi2O7:Ce3+ phosphors showed intense blue emission at about 425 nm, corresponding to the transitions from the lowest 5d excited state to the 2F5/2 and 2F7/2 spin orbit 4f ground states of Ce3+ ions, under optimal excitation of 349 nm. Under excitation of Ce3+ ions at 349 nm, the emission spectra of NaBaScSi2O7:Ce3+,Tb3+ phosphors consisted of a blue emission band of Ce3+ ions at 425 nm and a series of strong green emission lines at 488, 542, 582, and 625 nm due to the 5D4 → 7FJ (J = 6, 5, 4, and 3) characteristic transitions of Tb3+ ions. A possible energy transfer mechanism was proposed and ascribed to the dipole–dipole interaction on the basis of the experimental results and analysis. In addition, the cathodoluminescence properties of NaBaScSi2O7:Ce3+,Tb3+ were also studied in detail. The current results indicate that NaBaScSi2O7:Ce3+,Tb3+ can serve as a potential phosphor for application in UV-WLEDs and FEDs.

Controlling and revealing the trap distributions of Ca6BaP4O17:Eu2+,R3+ (R = Dy, Tb, Ce, Gd, Nd) by codoping different trivalent lanthanides

Thermoluminescence (TL) glow curves of Ca6BaP4O17:Eu2+,R3+ (R = Dy, Tb, Ce, Gd, Nd) samples were measured above room temperature in order to compare the trap distributions in the band gap. The observed phenomenon indicates that R3+ ions (R = Dy, Tb, Ce, Gd, Nd) have different effects on the trap properties of the Ca6BaP4O17:Eu2+ phosphor. The most shallow trap (0.620 eV) for the Tb3+ ion and the deepest trap (0.762 eV) for the Dy3+ ion eventually led to shorter duration (4.3 h and 1.2 h, respectively), while the appropriate trap depth (0.716 eV) for the Nd3+ ion makes the Ca6BaP4O17:Eu2+,Nd3+ sample show the longest afterglow duration (37.9 h). Codoping the Tb3+ ion slightly increases the instinct traps of the Ca6BaP4O17:Eu2+ sample and creates a new low-temperature TL peak corresponding to a relatively shallow trap leading to the strongest initial afterglow brightness (0.887 cd m−2), while codoping with other R3+ ions (R = Dy, Ce, Gd, Nd) creates new appropriate or inappropriate traps. By recording a series of long-lasting phosphorescence (LLP) spectra with various irradiated times and TL experiments with varying delay time after ceasing the UV irradiation, the trap distribution of the depth and shape was evaluated. The result provides a better understanding of the role of these trapping centers played in the persistent luminescence mechanism.

Luminescent and magnetic properties of the afterglow phosphors GdSr2AlO5:RE3+ (RE3+ = Eu3+, Sm3+, Pr3+ and Dy3+)

Novel afterglow phosphors based on the GdSr2AlO5 host were prepared by solid-state reaction under reductive atmosphere. The photoluminescence, afterglow, thermoluminescence and magnetism properties of GdSr2AlO5:RE3+ (RE3+ = Eu3+, Sm3+, Pr3+ and Dy3+) were discussed in detail for the first time in this paper. By doping appropriate rare earth ions into the GdSr2AlO5 host, all phosphors showed a satisfactory long-wavelength afterglow phenomenon and excellent paramagnetism characteristics. The mass magnetic susceptibility value was determined to be approximately 4.4052 × 10−5 emu g−1 Oe−1.

Determining the max effective trap depths of persistence luminescence by using trap depths continuous distributed phosphor

A bluish-white long persistence phosphor SrSiAl2N2O3:0.001Eu2+ was synthesized and its persistent luminescence and thermoluminescence properties were studied. Its afterglow time was 2490s. Its 1/t afterglow decaying behavior, broadness and highly high-temperature sides overlapping of the fading thermoluminescence curves indicated a trap depths continuous distributed condition. By subtracting the fading thermoluminescence curves from the least faded ones separately as an extension of the decay-time method, we found that almost all the resulting curves of the phosphor had similar valleys located in a narrow temperature range 140~150°C. This temperature range did not notably change with different fading times. Converted by Urbachs peak position method, this teperature range corresponded to an energy range of 0.826~0.846eV which gave an upper limit of trap depths having contribution to the afterglow performance. As this temperature range is fading time independent, it can be a useful characteristic temperature for trap depths, continuous distributed long persistence phosphors both in application and theory.