Abstract：3d transition metal（3d-TM） activated phosphors exhibit great potential applications in relevant fields. Generally， how to determine the ground state position of 3d-TM ion and engineer their valence state is significantly important in designing phosphor with target properties. This article reviews the spectroscopic data and optical transition levels of 3d-TM activated phosphors. Combining with the first-principle calculations， the evolution principle of the 3d-TM ground state in compounds is summarized. The charge transition tendencies and their theoretical understanding is revealed. Finally， the future design methods are prospected with above principles.
Keywords：3d transition metal ions;Ground state energy level;Luminescence property engineering
Abstract：Whispering gallery mode（WGM） microcavity laser is a micro/nano laser device which can confine light in micro/nano resonant cavity and maintain stable traveling wave transmission mode. With its high quality factor and small mode volume， WGM microcavity laser has the advantages of low threshold and narrow linewidth. It has become a hot research field at home and abroad. WGM microcavity has a very high optical energy density， and the interaction between light and material is significantly enhanced. In recent years， researchers have combined different gain materials with different microcavity structures， which has greatly promoted the development of WGM microcavity lasers. Based on the overview of the characteristic parameters and coupling mode of WGM microcavity lasers， this paper introduces the research results of several typical WGM microcavity lasers， including droplet microcavity， glass microcavity and semiconductor microcavity， and compares their performance parameters. The applications of the devices in ultra sensitive sensing， microwave photonics and on-chip integration are described， and the development trend of WGM microcavity lasers is prospected.
Keywords：whispering gallery mode;droplet microcavity;rare earth doped glass microcavity;semiconductor material microcavity;two dimensional material gain medium
Abstract：Micro-lasers have wide application prospects in optical communication， holographic technology， biomedical imaging and other fields. Surface plasmon polariton（SPP） propagates along the metal surface， which can be used to fabricate low-threshold nanolasers that break the diffraction limit.. They not only have the characteristic of small size， but also can induce the Purcell effect， so that the spontaneous emission efficiency can be significantly enhanced. In recent years， SPP lasers based on metal-insulator-semiconductor（MIS） waveguide structures have attracted much attention because of their ability of extremely large mode constraint. In this paper， SPP lasers based on MIS waveguide structures will be reviewed. Firstly， the basic mechanism of SPP laser is introduced， and the working principles of nanoplatelet type and nanowire type SPP lasers based on MIS waveguides are introduced respectively. Then， according to different gain medium materials， this paper introduces the research progress of SPP MIS waveguide lasers whose gain media are Ⅱ-Ⅵ semiconductor， Ⅲ-Ⅴ semiconductor and perovskite respectively. Finally， the thesis is summarized， and the future development and challenges of SPP MIS waveguide lasers are prospected.
Abstract：Broad-spectrum near-infrared light sources have a wide range of applications in non-invasive detection， military surveillance， food inspection， medical imaging， etc. In practical applications， a near-infrared（NIR） phosphor and a blue LED chip are used to form a fluorescent conversion light-emitting diode. As a NIR light source， it has the advantages of mature technology， compact structure and low cost. In this paper， the research progress of Cr3+ doped near-infrared phosphors excited by blue LEDs is reviewed. First， the crystal field theory of Cr3+ luminescence is briefly introduced， and the recently reported Cr3+ doped near-infrared phosphors are sorted out according to the material system. Secondly， in view of the shortcomings of near-infrared phosphors in terms of spectral range， temperature resistance， output power， electro-optical conversion efficiency， etc.， the existing research work from related mechanisms to optimize spectral performance， improve thermal quenching performance and electro-optical conversion efficiency is summarized. Finally， the researches on the device application of NIR light source are comprehensively summarized and compared.
Abstract：In this tutorial review， we present nonradiative energy transfer（ET） rates between lanthanides in a rearranged form. We emphasize the nature of the contributions which are different from those developed by Förster and Dexter theories because of the unique properties of the lanthanide ions. The expressions discussed here were based on Kushida's approach （electric multipolar mechanisms： dipole‑dipole（）， dipole‑quadrupole（）， and quadrupole‑quadrupole（）） within the Judd-Ofelt framework for 4f-4f transitions. Notice that these mechanisms were extended to include the exchange（） and magnetic dipole‑magnetic dipole mechanisms（）， and were improved to include shielding effects as well as an analytical expression for the F-factor （density of states in Fermi’s golden rule）. Similar to the original approach of Kushida， only the Forced Electric Dipole（FED） contributions to the Judd-Ofelt intensity parameters should be considered. A detailed discussion of selection rules and matrix elements calculations for the magnetic dipole‑magnetic dipole interaction is presented. In addition， step-by-step examples of Tb（Ⅲ）-Eu（Ⅲ） and Yb（Ⅲ）-Er（Ⅲ） energy transfer rates calculations are provided， with extensive Supporting Information， including scripts for calculations.
Keywords：nonradiative energy transfer;lanthanides;theoretical calculations;Ln-Ln energy transfer rates;selection rules
Abstract：Pyrimidine can be used as a common acceptor for the construction of D-A type thermally activated delayed fluorescent（TADF） materials. Its strong electron absorption characteristics and flexible substitution effect are advantageous to the formation of diversified molecular structures， which lends probability to realize efficient organic electroluminescence. In recent years， important progress has been made in the molecular structure design based on pyrimidine acceptor. The research direction has transformed from symmetrical molecules dominated by D-A-D type to asymmetric molecules gradually. Quinazoline is a new acceptor of TADF materials with fused bicyclic structure of benzene and pyrimidine rings， which shows good potential as a result of extended conjugate plane. Through the reasonable molecular modification， it can improve the luminescence performance of the device effectively. In this review， we summarize the research progress of thermally activated delayed fluorescent materials based on pyrimidine and its derivative quinazoline acceptors briefly with molecular structure， photophysical properties and device performances， and look forward to the broad development prospect of TADF materials based on quinazoline.
Abstract：Mid-infrared laser at 3-5 µm has important applications in the fields of photoelectric countermeasures， laser medical treatment， harmful gas detection. Rare earth ion doped crystal can be used as gain medium to realize mid-infrared laser output. Dysprosium doped lead thiogallate（Dy∶PbGa2S4，Dy∶PGS） crystal is a mid-infrared laser medium material with excellent performance and potential application value under the advantages of relatively low phonon energy and large electron energy gap. In this paper， the research progress of mid-infrared Dy∶PGS solid state lasers is reviewed， with emphasis on the output characteristics of continuous or pulsed lasers pumped at different wavelengths， and its future development directions are discussed.
Abstract：Space division multiplexing technology based on few-mode fiber（FMF） and multi-core fiber is considered to be one of the most important technologies to greatly improve the data transmission capacity of a single fiber in the future. If we want to employ FMF in space division multiplexing to realize a long-haul transmission system， few-mode erbium-doped fiber amplifiers（FM-EDFAs） will be a key block to compensate for the fiber transmission loss while its performance is determined by few-mode erbium-doped fiber（FM-EDF）. In addition to fundamental indexes like gain， bandwidth and noise figure， few-mode erbium-doped fiber has a unique index—differential modal gain（DMG） compared with the single-mode erbium-doped fiber. Minimizing DMG to maintain signal quality is critical in FM-EDFAs as the high differential modal gain can improve the potential for system outage. In this paper， the generation mechanism and improvement strategies of differential modal gain are systematically described， the different designs of FM-EDF are summarized， the performance characteristics of FM-EDF based on different pumping methods and different designs are compared， and the research on the performance of FM-EDF is prospected.
Abstract：LuAG∶Ce3+ is an efficient and stable commercial green phosphor-converted material. Two series of Lu3Al5-xMxO12∶Ce3+ transparent ceramics（TCs） doped with Ga3+/Sc3+ ions were fabricated by vacuum sintering. The effects of doping ions and their concentration on crystal structure， fluorescence properties， and thermal stability were investigated. Both Ga3+ and Sc3+ doped LuAG∶Ce3+ samples exhibit a blue-shift under 450 nm blue light excitation. Significantly， Ga3+ doped samples have more effective spectral modulation， and the emission spectrum shifts from 536 nm to 506 nm when Ga3+ concentration increases from 0% to 20%. Meanwhile， it is found from temperature-dependence spectrum and quantum yield characterization that Ga3+ doped ions have less impact on thermal stability of LuAG∶Ce3+ ceramics. By encapsulating the ceramic samples on 3 W blue LED chips， green light sources with various spectra were obtained. Among them， Ga3+ doped LuAG∶Ce3+ samples show better color tunability and maintain higher light efficiency. In summary， Ga3+ doped LuAG∶Ce3+ ceramic is a promising green phosphor-converted material.
Keywords：LuAG;transparent ceramics;green color converter;temperature-dependence spectrum
Abstract：In this paper， the luminescence process of Cs0.05FA0.81MA0.14PbI2.55Br0.45（hereinafter referred to as CsFAMA mixed cationic perovskite） thin film was studied by steady-state and transient photoluminescence（PL） spectroscopy. The phase transition induced PL spectra red shift was observed at about 245 K. According to the results of Saha-Langmuir equation， it is confirmed that electron hole recombination dominates the luminescence process of CsFAMA mixed cation perovskite when the temperature is higher than 65 K. The PL spectra of CsFAMA mixed cation perovskite were fitted by the combined model of interband luminescence and band tail luminescence. The band tail extendsion E0（0.023-0.045 eV） and the carrier equivalent temperature were obtained in the temperature range of 65-295 K. The experimental results show that the electron hole recombination rate constant Reh decreases with the increase of thermodynamic temperature（65-295 K） on the basis of analysis of the luminescence kinetics curve of CsFAMA mixed cationic perovskite. The increase of thermodynamic temperature causes the enhancement of lattice vibration， which is conducive to the heat exchange between free carriers and lattice. Meanwhile it increases the thermal disorder， leading to suppress of electron and hole radiative recombination and accelerate of carrier nonradiative recombination.
Abstract：With the advantages of small size， high beam quality， strong laser brightness and fast response speed， microlasers show great application potential in military， medical， communication and other fields. As a core part of microlaser， the gain medium is a kind of material with amplified spontaneous emission ability， which plays an important role in laser properties and directly affects the threshold， laser energy， stability and wavelength tuning performance of microlaser. In recent years， various advanced materials with amplifying spontaneous emission property have been developed， and they have emerged in various microlasers. In this review， the working principle of the amplified spontaneous emission for the gain medium in the laser was firstly introduced. Secondly， the characteristics of optical gain media for microlasers and the research status of laser from different modes of optical resonators were systematically summarized. Finally， the current problems and solutions of amplified spontaneous emission materials were put forward， and the future development was prospected. This review will be beneficial to the research and development of microlasers.
Abstract：Light sources with wavelengths in the green region are very important for a wide gamut of applications， including solid-state lighting， visible light communications， agriculture， optogenetics， and so on. Compared to blue light-emitting diodes（LEDs）， the fabrication of high-performance low-dimensional green LED has long been limited by “Green gap” and “Efficiency droop”. In this work， a kind of green LED composed of p-type InGaN layers and a single Ga doped ZnO microwire（ZnO∶Ga MW） was designed. The experiment results indicated that this LED device had a central wavelength located at 540 nm and a linewidth of about 32 nm. Most important of all， increasing the operating current at high level， no noticeable variations in the electroluminescence characteristics and relative external quantum efficiency（REQE） could be observed. Additionally， a cladding of Au nanofilm was introduced on the surface of microwire to optimize the interface quality of n-ZnO∶Ga MW/p-InGaN heterojunction， resulting in the better uniform contact between ZnO∶Ga and InGaN， and the higher output intensity. This work demonstrates that such heterojunction composed of n- ZnO∶Ga and p-InGaN is a promising candidate for fabricating a new generation of high-brightness microscale green LEDs.
Abstract：A metal-semiconductor-metal（MSM） structure solar blind UV detector was constructed by preparing interdigital Au electrode on polycrystalline diamond films grown by DC plasma jet chemical vapor deposition （DC-PJCVD）. The effects of different photolithography processes on the performance of the diamond detector were studied， and the results show that the performance of the device prepared by lift-off photolithography is significantly better than that prepared by wet procedure photolithography. The photocurrent of the device is increased by 4.4 times， the light-dark current ratio is increased by 6.8 times， and the responsivity is increased by 9 times to 0.15 A/W at 25 V. On this basis， the interdigitated electrodes of Au， Ti， Ti/Au and Ag were prepared by lift-off photolithography. The performance differences of diamond UV detectors prepared by different metal electrodes were compared. The Ag electrode has the best performance among the four electrodes due to the gain caused by the barrier tunneling effect. At 25 V bias， the light current is 0.21 μA， and responsivity increases to 0.78 A/W. Compared with common Au electrode， the photocurrent， light-dark current ratio and responsivity are increased by 5.2 times， 7 times and 5.2 times respectively.
Abstract：One of the prerequisites for realizing high efficiency photovoltaic devices is that the incident light is effectively absorbed by the light absorbing layer. Therefore， it is very important to improve efficiency to systematically analyze the optical loss mechanism of perovskite photovoltaic cells and optimize the light absorption of the light absorbent layer. In this paper， for inverted planar perovskite solar cells， combining with the external quantum efficiency（EQE） of the cell， the light absorption characteristics of the film and theoretical simulation， the effects of the thickness changes of perovskite thin film as the light absorption layer and ［6，6］-phenyl-C61-butyric acid methyl ester（PCBM） thin film as the interface layer on photogenerated current were compared and studied. The results show that， in addition to parasitic absorption， the adjustment of the optical field by the interface layer can affect the optical absorption of the light absorption layer in the device. The simulation results show that 660 nm perovskite film and 40 nm PCBM film can be used as the optimal choice， and the corresponding integral current is 24.93 mA/cm2. This paper also explored the influence of the addition of PbI2 layer on the absorption characteristics of the perovskite light absorbing layer. The results indicate that when PbI2 accumulates on the side of the perovskite layer near the incident light， it leads to significant optical loss. However， when PbI2 accumulates on the side of the perovskite layer near the back electrode， the influence is relatively small.
Abstract：Micro light-emitting diode（Micro-LED）， with many advantages such as high-resolution， high color gamut， and high stability， has broad prospects for near-eye display. However， two major technical issues in Micro-LED need to be solved， including mass electroluminescence detection and mass metal bonding. In this work， a working mode for Micro-LED with single-terminal carrier-injection is proposed， and a single-injection type Micro-LED related to the working mode is fabricated. The working process is studied by experiments and simulations in order to explore the working mechanisms. The current-voltage， current-frequency， brightness-frequency relationship and the periodic variation of the energy band of single-injection type Micro-LED under sinusoidal alternating current are studied. Moreover， the carrier transport model of single-injection Micro-LED is proposed. Finally， the application of single-injection mode used in the detection of vertical structure Micro-LED is demonstrated， which provides new ideas for Micro-LED detection.
Keywords：micro-LED;Single-terminal carrier-injection;Electroluminescence detection;Alternating current
Abstract：In this study， response surface methodology（RSM） was used to study the effects of microwave action time （T）， microwave power（W） and the ratio of common lophatherum herb to deionized water （R） on the fluorescence quantum yield （QY） of N/Si-CQDs prepared by microwave method. The significance order of the influence of the above process parameters on QY， and the corresponding QY regression model and the best process parameters are obtained， and the optimization results are proved to be reliable through validation experiments. The average particle size of N/Si-CQDs obtained by the best process is small and evenly distributed， with good dispersion in water， excitation dependent emission characteristics， high fluorescence stability， low cytotoxicity to HEK293 cells. And the N/Si CQDs can be absorbed by cells to illuminate cells， so as to clearly distinguish cytoplasm and nucleus， which shows that the N/Si-CQDs can be used for cell imaging. This study not only provides a new idea for the high-value utilization of bamboo leaves， but also has reference value for improving the efficiency of microwave preparation of biomass carbon quantum dots and promoting their application in biomedical fields such as cell imaging.