Haoyi Wu

Multifunctional near-infrared emitting Cr3+-doped Mg4Ga8Ge2O20 particles with long persistent and photostimulated persistent luminescence, and photochromic properties

Here we report a series of multifunctional Cr3+-doped magnesium gallogermanate particles. Several minutes of ultraviolet (UV) light excitation can lead to strong near-infrared (NIR) long persistent luminescence (LPL) at 600–850 nm with a long lasting time of at least 25 h. After the disappearance of LPL, NIR photostimulated persistent luminescence (PSPL) can be rejuvenated repeatedly several times by an external photostimulus (visible or NIR light). Meanwhile, the material shows photochromic (PC) properties, i.e., the surface color can change reversibly between white/pale green and rosybrown with high fatigue resistance by alternating UV and visible light irradiation. When the temperature is increased to 300 °C, the induced rosybrown surface color can also be bleached. This new multifunctional material has potential applications in a wide range of fields, such as in vivo bio-imaging, optical information write-in and read-out media, erasable optical memory media and optical sensors. The continuous trap distribution and modulation were characterized. The optimum trap depth was determined to be 0.51–0.86 eV. In addition, we gained insight into the mechanism of multifunctional properties and the interconnection between them.

Controllable optical properties by ratio of Sr/Ca in Sr1.97?xCaxMgSi2O7?:? {\rm Eu}_{0.01}^{2+} , {\rm Dy}_{0.02}^{3+} phosphors

The long afterglow phosphors Sr1.97−xCaxMgSi2O7 :  , (x = 0, 0.4, 0.8, 1.2, 1.6, 1.97) were synthesized by the high temperature solid-state reaction method. The phases were analyzed by x-ray powder diffraction. All the samples have a similar structure. A slight shift of the peaks, which implied a change of crystal plane spacing, was found. With a decrease in the Sr/Ca ratio, the crystal plane spacing became smaller. The red shift was found in the emission spectra, from 468 to 529 nm. The 5d level of the Eu2+ ion splits into two sets. With the decrease in the crystal plane spacing, the energy of one set becomes higher while the other one becomes lower. This leads to the red shift of the emission spectra. The afterglow time becomes shorter with the decreasing Sr/Ca ratio. The thermoluminescence curves, which imply the depth of the traps, conform to the various afterglow times of the samples. This is due to the greater ionization potential of the Dy ions with the decreasing crystal plane spacing.

Luminescent properties of a green long persistent phosphor Li 2 MgGeO 4 :Mn 2+

A novel rare-earth ion free phosphor, Mn2+-activated Li2MgGeO4, was prepared by a high temperature solid-state reaction method. The phase structure was identified by XRD. We reported on its photoluminescence and long persistent luminescence properties. The green emission with a broad band centered at 525 nm corresponds to the 4T1(4G)–6A1(6S) transition of the Mn2+ ions. After irradiation by 254 nm UV light, green long persistent luminescence can be observed and last at least 5 h. Thermoluminescence was studied and the long persistent luminescence mechanism was also discussed in detail.