Jianyan Ding

Novel red and green emitting Li2SiN2:Eu3+/Tb3+ phosphors with a broad charge transfer band

In this work, a broad excitation band of Li2SiN2:Eu3+ with the peak at 357 nm has been found and investigated. The photoluminescence, morphologies and thermal stability of the samples were also measured. Under excitation at 357 nm and 300 nm, sharp red and green light can be observed due to the 5D0–7F2 transition of the Eu3+ ions and the 5D4–7F5 transition of the Tb3+ ions, respectively. According to the Diffuse reflectance spectra in combination with the energy level diagram of Li2SiN2:0.02Eu3+, we deduced that the broad excitation bands belong to the charge transfer band (CTB), which have also been observed in Li2SiN2:Tb3+ with the peak at 271 nm. And the thermal stabilities of the samples have been found to be connected with the CTB.

A novel self-activated white-light-emitting phosphor of Na2TiSiO5 with two Ti sites of TiO5 and TiO6

In this work, a novel self-activated light emitting phosphor of Na2TiSiO5 (NTSO) has been successfully synthesized in a high temperature solid-state reaction. The photoluminescence (PL) and cathodoluminescence (CL) properties of NTSO have been measured. Under excitation at 260 nm, NTSO emits a white light with CIE chromaticity coordinates (0.275, 0.355) and cyan light can also be observed at low voltage excitation. The crystal structure of NTSO has been investigated using the Rietveld refinement, which shows that Ti ions not only occupy the octahedron center but also connect with five O ions to form a TiO5 polyhedron. The special polyhedron of TiO5 broadens the emission band, and the energy transfer between the two sites has also been proved through the time-resolved photoluminescence (TRPL) spectra. Finally, the CL properties of NTSO with the functions of accelerating voltage, filament current and electron radiation time have been measured and the results show that NTSO emits bright light, and has excellent stability and good CIE chromaticity coordinates, which indicates that NTSO has the potential to be applied in FEDs.

Synthesis, Crystal Structure, and Luminescence Properties of Tunable Red-Emitting Nitride Solid Solutions (Ca1–xSrx)16Si17N34:Eu2+ for White LEDs

A series of nitride solid solutions (Ca1-xSrx)16Si17N34:0.03Eu2+ were successfully synthesized through the conventional solid-state method. The electronic crystal structure and photoluminescence characteristics were studied in detail. The excitation in the near-ultraviolet and blue regions of the samples shows a broad band in the 250-550 nm range, which can match well with the n-UV and blue lighting-emitting diode chips. Partial substitution of Ca2+ by Sr2+ results in a redshift emission, and the impacts of Sr content on the luminescence were researched in detail. Under 410 nm excitation, the phosphor exhibited tunable red emission from 616 to 653 nm by changing the concentration of Sr2+. Based on the crystal data, the emission can be fitted into three distinguished Gaussian components, which are attributed to the different Eu2+ luminescence centers occupied in three disparate Ca2+ (Sr2+) lattice sites. The temperature quenching property of the phosphor was also investigated, and the good thermal stability of the phosphors was analyzed through the activation energy for thermal quenching. And the obtained CCT values from 2642 to 2817 K are suitable for a warm white light region. All the results indicated that the phosphors have possible application in the warm white light-emitting diodes.

Effect of a solid solution of AlN on the crystal structure and optical properties of LiSi2N3:Eu phosphors

The solid solutions of nitridosilicate phosphors LiSi2N3:Eu-xAlN (0 ≤ x ≤ 0.35) were synthesized using a gas-pressed sintering in this work. The effects of a solid solution of AlN on crystal structure, morphology, thermal stability and luminescence properties were studied. The luminescence intensity of LiSi2N3:Eu phosphor is significantly improved by the solution of AlN, but the emission position is unchanged. The emission intensity of LiSi2N3:Eu0.01-0.30AlN is about 2.17 times that of LiSi2N3:Eu0.01. The results show that these solid solutions could be the most useful way to improve the luminescence intensity of LiSi2N3:Eu phosphors.

K4CaGe3O9:Mn2+,Yb3+: a novel orange-emitting long persistent luminescent phosphor with a special nanostructure

In this work, a novel germanate-based orange-emitting long persistent luminescent (PersL) phosphor, K4CaGe3O9(KCGO):Mn2+,Yb3+, has been successfully synthesized via a solid-state reaction. The special nanostructures of KCGO:Mn2+ and KCGO:Mn2+,Yb3+ were indicated by transmission electron microscope (TEM) images, where the block particles of these samples are shown to consist of many irregular spherical nanoparticles and the size of these spherical particles is less than 10 nm. This special nanostructure contains many defects and could provide the preconditions for the PersL properties of KCGO:Mn2+. Furthermore, after co-doping with Yb3+, the PersL properties are effectively improved due to the high concentration of new traps caused by the non-equivalent substitution of Yb3+. With the optimum doping concentration and sufficient excitation with UV light, the afterglow of KCGO:0.02Mn2+,0.015Yb3+ can persist over 5 h above the recognizable intensity level (≧0.32 mcd m−2). Both the fluorescence and phosphorescence spectra of KCGO:Mn2+,Yb3+ exhibit only one broad emission band, which belongs to the 4T1(G)–6A1(S) transition of Mn2+. In addition, with the help of thermoluminescence (TL) curves, the processes and possible mechanism are studied and discussed.