Low temperature photoluminescence study of Ga As defect states

Low temperature(77 K)photoluminescence measurements have been performed on different GaAs substrates to evaluate the GaAs crystal quality.Several defect-related luminescence peaks have been observed,including 1.452 eV,1.476 eV,1.326 eV peaks deriving from 78 meV GaAs antisite defects,and 1.372 eV,1.289 eV peaks resulting from As vacancy related defects.Changes in photoluminescence emission intensity and emission energy as a function of temperature and excitation power lead to the identification of the defect states.The luminescence mechanisms of the defect states were studied by photoluminescence spectroscopy and the growth quality of GaAs crystal was evaluated.

Study of the Electronic Structure and Optical Properties of Rare Earth Luminescent Materials

Rare earth luminescent materials have attracted significant attention due to their wide-ranging applications in the field of optoelectronics. This study aims to delve into the electronic structure and optical properties of rare earth luminescent materials, with the goal of uncovering their importance in luminescence mechanisms and applications. Through theoretical calculations and experimental methods, we conducted in-depth analyses on materials composed of various rare earth elements. Regarding electronic structure, we utilized computational techniques such as density functional theory to investigate the band structure, valence state distribution, and electronic density of states of rare earth luminescent materials. The results indicate that the electronic structural differences among different rare earth elements notably influence their luminescence performance, providing crucial clues for explaining the luminescence mechanism. In terms of optical properties, we systematically examined the material’s optical behaviors through fluorescence spectroscopy, absorption spectroscopy, and other experimental approaches. We found that rare earth luminescent materials exhibit distinct absorption and emission characteristics at different wavelengths, closely related to the transition processes of their electronic energy levels. Furthermore, we studied the influence of varying doping concentrations and impurities on the material’s optical properties. Experimental outcomes reveal that appropriate doping can effectively regulate the emission intensity and wavelength, offering greater possibilities for material applications. In summary, this study comprehensively analyzed the electronic structure and optical properties of rare earth luminescent materials, providing deep insights into understanding their luminescence mechanisms and potential value in optoelectronic applications. In the future, these research findings will serve as crucial references for the technological advancement in fields such as LEDs, lasers, and bioimaging.

Alcohol Solvent Effect on Fluorescence Properties in the Solvothermal Synthesis of Carbon Quantum Dots

Highly monodisperse carbon quantum dots(CQDs)were synthesized by a solvothermal method using L-ascorbic acid as carbon source and different simple alcohols(methanol,ethanol,ethylene glycol,and isopropanol)as reaction solvents at 180℃for 4 hours.The performance of CQDs was characterized by transmission electron microscope(TEM),Fourier infrared spectrometer(FTIR),UV-visible spectrophotometer,and fluorescence spectrophotometer.The results show that the prepared CQDs are wavelength-dependent,and have good hydrophilicity and similar surface compositions.However,there are more carbon and oxygen-containing functional groups on the surface of CQDs prepared with ethanol(CQDs-ET),and the type and number of functional groups will directly affect the fluorescence emission of CQDs.Also,it is found that the luminescence mechanisms of CQDs prepared by this solvothermal method are mainly based on the defect state of the oxygen group surface.And alcohol solvents do not directly participate in the formation of carbon nuclei during the reaction process,but it will affect the number and type of surface groups.Therefore,the influence of surface groups on the CQDs performance is greater than that of carbon nuclei in this experiment.

Mechanisms and absolute quantum yield of upconversion luminescence of fluoride phosphors

Mechanisms of upconversion luminescence（UCL） of SrF2：Er phosphors corresponding to the 4G11∕2→4I15∕2,2H9∕2→4I15∕2,4F5∕2→4I15∕2,4F7∕2→4I15∕2,2H11∕2→4I15∕2,4S3∕2→4I15∕2,4F9∕2→4I15∕2, and 4I9∕2→4I15∕2 transitions upon excitation of the 4I11∕2 level of Er3＋ions were investigated. Energy transfer upconversion processes are responsible for the populating of the 2H9∕2,2H11∕2,4S3∕2, and 4F9∕2 levels. Cooperative process is the dominant mechanism of luminescence from 4S3∕2 and 4F9∕2 levels for SrF2：Er with high concentrations of Er3＋ions. The UCL from 4G11∕2 and 4F5∕2 is explained by excited-state absorption. Cross-relaxation processes take part in the population of 4F9∕2 and 4I9∕2 levels. For quantifying material performance, the Er3＋-concentration dependence of UCL and the absolute quantum yields of SrF2：Er were studied. The most intensive visible luminescence was obtained for SrF2：Er（14.2%） with 0.28% maximum quantum yield.

Investigation of the mechanism of upconversion luminescence in Er^(3+)/Yb^(3+) co-doped Bi_2Ti_2O_7 inverse opal

Three-dimensional-ordered Yb/Er co-doped Bi2Ti207 inverse opal, powder, and disordered reference sam- ples are prepared and their upconversion （UC） emission properties and mechanisms are investigated. Sig- nificant suppression of UC emission is detected when the photonic band-gaps overlap with Er3＋ UC green emission bands. Interestingly, green and red UC emissions follow a two-photon process in the powder sample but a three-photon one in the inverse opal.

Ultralong room temperature phosphorescence via the charge transfer-separation-recombination mechanism based on organic small molecule doping strategy

Ultra-long room temperature phosphorescence(URTP) has been increasingly recognized in pure organic luminophor in recent years. Through a simpler molecular design and charge separation-recombination pathway, organic luminophor can achieve even better URTP properties. In this work, we achieved URTP in a system of host-guest doped benzophenone derivatives whose phosphorescence is visible to the naked eye. The differences in the wavelength lifetimes of luminescent emission correspond to different photophysical mechanisms. Through a combination of theoretical calculations and experiments, the host acts as a powerful substrate that restricts the motion of the guest and inhibits the non-radiative transitions of the guest, accompanied by a charge transfer separation-recombination process between the host and the guest, resulting in an URTP phenomenon. Transient absorption results demonstrate the existence of a charge-separated state. The design strategy via charge separation is generic and easy to implement,providing a direction for the future design of doped URTP.

Novel strategy of multidimensional information encryption via multi-color carbon dots aggregation-induced emission

Carbon dots(CDs)with aggregation-induced emission(AIE)have sparked significant interest in multidimensional anti-counterfeiting due to their exceptional fluorescence properties.However,the preparation of AIE CDs with multicolor solid-state fluorescence remains a formidable challenge due to its complicated construction.In the present work,a novel class of multicolor AIE CDs(M-CDs)were fabricated using selected precursor(salicylic acid,thiosalicylic acid,and 2,2'-dithiodibenzoic acid),with an eco-friendly,low-cost one-pot solvothermal method.In the dilute organic solution,M-CDs manifested blue emission,but upon aggregation in the presence of water,the red,yellow,green,and blue emissions were displayed due to the AIE effect.Structural analysis,coupled with theoretical calculations,revealed that the increase in the size of sp2 domains would lower the Eg and cause a red-shift emission wavelength.Significantly,the continuous emission of M-CDs from blue to red can be utilized as ink for multimode printing,enabling the creation of a variety of school badges and quick response codes.These findings hold promising implications for multi-information encryption applications.

Long afterglow yellow luminescence from Pr^(3+) doped SrSc_(2)O_(4)

A yellow emitting long afterglow luminescence material SrSc_(2)O_(4):Pr^(3+)was successfully prepared by solid state reaction method.SrSc_(2)O_(4):Pr^(3+)phosphor shows a long afterglow luminescence peak at about 495,545,621,630 and 657 nm,respectively,corresponding to the f–f transitions of Pr^(3+).The afterglow chromaticity coordinates of SrSc_(2)O_(4):1 at%Pr^(3+)were calculated to be(0.35,0.41),indicating that the afterglow emission is close to the light of yellow region.And,the afterglow luminescence of the optimal sample doped by 1 at%Pr^(3+)can persist for over 3 h.The thermoluminescence results suggest that there are three types of traps with depth of 0.61,0.69 and 0.78 eV exiting for all the samples,which are produced by the addition of Pr^(3+)ions.The trap density of SrSc_(2)O_(4):1 at%Pr^(3+)is the maximum when the incorporation of Pr^(3+)ions reaches 1 at%,which thus results in the longest afterglow luminescence.All the results indicate that SrSc_(2)O_(4):Pr^(3+)can be a potential candidate of novel long afterglow phosphors.

Recent advances in fluorescence imaging of alkaline phosphatase

Phosphatase plays a vital important role in many biological functions due to the dephosphorylation serves varied roles in cellular regulation and signaling.Among the family of phosphatase,alkaline phosphatase(ALP)could act as crucial prognostic indicators for many diseases such as bone diseases and cancer.However,the detection of ALP is mainly limited to in vitro colorimetric method in clinic.Therefore,huge efforts have been paid on the fluorescence imaging that provides a reliable method to detect the real-time and in vivo changes of the level of ALP.In this review,we summarize recent advances in fluorescence imaging of phosphatase,mainly focused on ALP.The imaging probes of phosphatase are mainly classified according to their luminescence mechanisms.In the end,we assessed the challenges and future prospects of phosphatase probes.