Studies on Self-Luminous Material and Coating with Long Persistent Yellow-Green Afterglow

The preparation, properties, expression and luminescent mechanism of self luminous material (SrAl 2O 4∶Eu 2+ , Dy 3+ ) were discussed. The long afterglow luminescent coating was prepared by adding proper luminescent powders SrAl 2O 4∶Eu 2+ , Dy 3+ and other aids into styrene/acrylic emulsion. The best prescription of the coating was defined. The properties of luminescent coating were determined. The primary factors which affect the coating properties were discussed.

Enhancement of upconversion luminescence due to the formation of nanocrystals in Er^(3+)-doped tellurite glasses

Optically transparent Er^3＋-doped tellurite-based nanocrystallized glasses with the composition of 70TeO2.15Li2O·15Nb2O5·0.5Er2O3 （mol） have been prepared bv a conventional melting quenching and the subsequent heat treatment processes. The sizes of grown nanocrystals in glass matrix appear to be 35-50 nm from the X-ray diffraction （XRD） measurement. The microhardness measurement shows that the Vickers hardness values of the nanoerystallized tellurite glasses are larger （33%-62%） than those in the base glass. The Raman spectra imply that the maximum phonon energy of the based glass decreases and shifts from 668 to 638 cm^-1 after heat-treatment. Visible upconversion luminescence and infrared luminescence of the base glass and heat-treated glasses under 980-nm laser diode （LD） excitation are investigated. The 524-, 546- and 656-nm upconversion intensities by 980-nm pumping increase significantly.

Organic Fluorescent Molecule with High Solid State Lumines- cent Efficiency and Protonation Stimuli-response

A novel organic fluorophor with high solid state luminescent efficiency based on 1,4-bis（2,2-di（pyridin-2-yl）- vinyl）benzene （BDP2VB） was designed and synthesized. It emits faintly in solution, but becomes a strong emitter in the aggregate state, demonstrating its aggregation induced emission （AIE） property. According to the crystal struc- ture analysis, J-type aggregation was formed in the packing mode of the molecule, which was demonstrated to be beneficial to gain high fluorescent quantum efficiency in solid state. Additionally, the emission color of BDP2VB can change dramatically in solid state as well as in solution by the protonation stimuli.

Effect of nanocrystals on up-conversion luminescence of Er^(3+),Yb^(3+) co-doped glass-ceramics

Different up-conversion luminescent spectra of Er^3＋ ions were observed in the oxyfluoride glass-ceramics. The ratio of two fluorides in the original compositions was modified in order to form different nanocrystals. The intensity of up-conversion luminescence increased sharply when the ratio of PbF2 and CdF2 was 40：10. The data of differential thermal analysis and X-ray diffraction were used to explain the optimization fluoride ratio. The intensity of up-conversion luminescence is not only decided by the crystallizability but also mainly related with the stoiehiometric proportion of fluoride nanocrystals in the glass-ceramics.

D-A structured high efficiency solid luminogens with tunable emissions： Molecular design and photophysical properties

Fabrication of efficient solid luminogens with tunable emission is both fundamentally significant and technically important. Herein, based on our previous strategy for the construction of efficient and multifunctional solid luminogens through the combination of diverse aggregation-induced emission （ALE） units with other functional moieties, a group of luminophores with electron donor-acceptor （D-A） structure and typical intramolecular charge transfer （ICT） characteristics, namely CZ-DCDPP, DPA-DCDPP and DBPA-DCDPP were synthesized and investigated. The presence of twisting and AlE-active 2,3- dicyano-S,6-diphenylpyrazine （DCDPP） moiety endows them highly emissive in the solid states, whereas the introduction of arylamines with varied electron-donating capacity and different conjugation render them with tunable solid emissions from green to red. While CZ-DCDPP and DPA-DCDPP solids exhibit distinct mechanochromism, both DPA-DCDPP and DBPA-DCDPP solids can generate efficient red emission. Owing to their high efficiency, remarkable thermal and morphological stabilities and moreover red emission, they are promising for diverse optoelectronic and biological applications.

Low threshold Nd^(3+):KY(WO_4)_2 laser operated at 1072 nm pumped by diode

The diode-pumped Nd：KYW laser operated in the free-running mode at 1072 nm is demonstrated at room temperature. The laser output power of 102.6 mW with 12.07% optical-to-optical conversion efficiency and 13.16% slope efficiency is obtained. The laser threshold is about 110 mW. Such a low threshold is in agreement with the theoretical prediction.

Generation of broadband and multiple-peak THz radiation in aperiodically poled lithium niobate

We theoretically analyze the generation of broadened and multi-peak terahertz （THz） radiation in aperiodically poled lithium niobate （APPLN）, whose sequence of opposite domains is optimized by simulated annealing （SA） algorithm. The full-width at half maximum （FWHM） of the broadened THz radiation in our simulation is 0.26 THz. Both of the central wavelength and FWHM can be easily tuned by choosing proper objective functions. THz radiation with wider and flatter FWHM can be achieved by increasing the length of the lithium niobate crystal. The two-peak THz generation is also provided as an example of multi-peak with the central wavelengths at 1.68 and 1.80 THz, respectively.

Coherent control of two-photon absorption of Pr^(3+) ion by shaped ultrashort laser pulses

Enhancing the photoluminescence and depressing the background emission are important problems in rare earth ion-doped materials. In this letter, the two-photon absorption （TPA） probability in a Pr3＋ ion system is enhanced by a factor of 12.3 by a π-phase step scanning of ultrashort laser pulses. This level is significantly higher than that achieved by a transform-limit pulse. However, the laser intensity of shaped pulse is reduced to 37% of the initial transform-limited pulse. In this method, the TPA probability can also be reduced to 58%. Furthermore, the el＇feet of the shift of the intermediate energy level and the bandwidth of final states on TPA probability is discussed.

Quantitative deviation of the two-photon absorption coefficient based on three laser pulse models

The pulse profile influence of excitation light on the two-photon absorption coefficient β is theoretically and numerically studied. Based on Gaussian spatial and temporal laser, we obtain an expansion formula of energy transmission. As compared with a plain beam and a pulse beam that is rectangular in time but Gaussian in space, the relative deviations of β turn out to be about 214% and 47%, respectively. These differences indicate that a smaller β may be obtained than the real one in usual nonlinear transmission. Our result suggests that by taking real pulse profile into account, a more exact β can be derived in energy transmission measurement.

Nonlinear two-photon absorption properties induced by femtosecond laser with the films of two novel anthracene derivatives

Two novel anthracene derivatives containing 4-vinylpyridine （FPEA） and 2-vinylpyridine （TPEA） poly（methyl methacrylate） films are prepared on quartz glass substrates. Their nonlinear absorption properties are investigated by using a 120-fs, 800-nm Ti：sapphire femtosecond pulsed laser operating at a 1-kHz repetition rate. The unique nonlinear absorption properties of these new compounds are observed by utilizing a Z-scan system. These two-photon absorption （TPA） properties are proven by the two-photon fluorescence excited at 800 nm. The FPEA and TPEA films have nonlinear TPA coefficients of 0.164 and 0.148 cm/GW and the TPA cross sections of 3.345 × 10^-48 and 3.081 × 10^-48 cm4 ·s/photon, respectively. The influence of the chemical structures on the nonlinear TPA properties of the compounds is also discussed. The highly nonlinear TPA activities of the films implied that the new anthracene derivatives are suitable materials with promising applications in super-high-density three-dimensional data storage and nano- or microstructure fabrication.

Theoretical analysis on two-photon absorption spectroscopy in a confined four-level atomic system

We investigate theoretically two-photon absorption spectroscopy modified by a control field in a confined Y-type four-level system. Dicke-narrowing effect occurs both in two-photon absorption lines and the dips of transparency against two-photon absorption due to enhanced contribution of slow atoms. We also find that the suppression and the enhancement of two-photon absorption can be modified by changing the strength of the control field and the detuning of three laser fields. This control of two-photon absorption may have some applications in information processing and optical devices.

Investigation of transient two-photon excited fluorescence in biological tissue

The fluorescence power from biological tissue excited by a femtosecond laser pulse compared with excitation power does not appear to obey a simple quadratic relationship given by the steady non-linear theory. A more reliable analysis is developed based on transient two-photon absorption because the response time of two-photon absorption is longer than the width of a femtosecond pulse. Good agreement is obtained between the theoretical analysis and the experimental results of fluorescence power versus excitation power. This letter offers potential value to non-linear optics in biological tissues.

Ion-π interactions for constructing organic luminescent materials

Organic luminescent materials are one of the research hotspots worldwide.The luminescent efficiency of these materials can be tuned by introducing noncovalent interactions.Ion-π interactions,mainly including anion-π interactions and cation-π interactions,are relatively new but powerful noncovalent interactions with extensive applications in supramolecular chemistry.The use of ion-π interactions to fabricate highly luminescent materials is initiated since they were introduced to develop aggregation-induced emission luminogens in 2017.Then,this research field is undergoing through challenging but very prospective developments.In this minireview,we start with a brief introduction of ion-π interactions and then make a summary of the reports on organic fluorescence based on ion-π interactions and room temperature phosphorescence induced by ion-π interactions.The applications of organic luminescent materials based on ion-π interactions in bioimaging,imaging-guided anticancer and antibacterial treatment are also discussed.The challenges and prospects of using anion-π and cation-π interactions for constructing organic luminogens are presented in the final part.It is expected that this minireview will provide some guidelines for fabricating novel organic luminescent materials and further extend the application potential of ion-π interactions.