Mn-related Emission Research Articles

Optical properties of Zn0.75Mg0.25O:Mn ceramics

Mn-doped ZnO, MgO and Zn0.75Mg0.25O samples ([Mn] = 0.1 at.%) were produced by conventional solid-state technique and investigated by means of XRD, EPR, absorption, photocurrent, photo- and cathodoluminescence methods. It was shown that Zn0.75Mg0.25O solid solution with hexagonal structure has the bandgap of Eg ∼3.65 eV. The quenching of host defect-related luminescence in ZnO:Mn and in hexagonal Zn0.75Mg0.25O:Mn was observed, while the Mn-related emission being absent. The energy level of MnZn2+ center in hexagonal Zn0.75Mg0.25O:Mn was found to be at 2.16 eV below conduction band (c-band) bottom and all excited states of MnZn2+ ions, including the lowest one, reside in c-band, as it takes place in ZnO:Mn. It is concluded that the necessary condition to obtain Mn-related light emission in Mn-doped alloys is to make deeper the lowest excited level of MnZn2+ ions. One of the solutions is to produce Zn1-xMgxO:Mn solid solution with the bandgap energy larger than 4.0 eV using nonequilibrium fabrication approaches.

Stability improvement of photoluminescent QLEDs based on Mn-doped all-inorganic metal halide perovskite quantum dots with silica shell

Perovskite quantum dots (PQDs) suffer from the long-time stability owing to their strong ionic structure. Wrapping them with silica or doping them with ions have been used to improve their structural stabilities. Here, transitional metal doping and surface engineering are employed to synthesize silica-coated Mn:CsPbCl3 QDs for the fabrication of photoluminescent QD-based light-emitting diodes (QLEDs). The as synthesized QDs have dual emission, one is the intrinsic emission of the perovskite host, and the other is the Mn-related emission. The as synthesized Mn-doped CsPbCl3 exhibit improved stability of luminous spectra compared to those of the pure ones. We also integrate the silica-coated Mn:CsPbCl3 QDs as color converters with a purple chip. The luminous spectra of the photoluminescent QD-based light-emitting diodes (QLEDs) can be adjusted by controlling the QD concentration. Twenty-day observation and measurement show that devices based on the silica-coated Mn:CsPbCl3 exhibit enhanced performance stabilities, including a maximum CRI fluctuation of 2.3, a maximum CCT fluctuation of 7 K and a maximum LER fluctuation of 5.2 lm/Wopt. These results indicate that manganese doping and silica shell are helpful for the stability improvement of perovskite QDs, and the potential applications of silica-coated Mn:CsPbCl3 QDs in lighting fields.

Modulation of the optical properties of ZnS QD-embedded glass through aluminum and manganese doping

Incorporation of Al3+ ions into ZnS QDs is found to induce VZn, which act as a dispersant to reduce the concentration quenching of the Mn-related emission and achieve energy transfer from the ZnS QDs to Mn2+ ions, long lifetime, and high PL QYs.

Absence of Mn emission in MnxZn(1-x)S thin films grown by spray pyrolysis technique

In the present investigation, the effect of manganese (Mn) dopant on zinc sulfide (ZnS) thin films used for blue light emitting diode was studied. The basic studies on the structural and morphological properties showed good crystallinity up to 2 at % Mn concentration. Samples were studied for the presence of defects using models of Urbach energy and near-edge absorptivity ratio (NEAR). Upon manganese doping, enhancement in the blue emission (in the wavelength region ~ 400 nm) was observed, and interestingly, the Mn related orange emission was not observed. Here, we explained the possible reasons for the suppression of this signature orange emission. Present work is compared with various other reports on manganese doped zinc sulfide (MnxZn(1-x)S). The properties of the MnZnS films were characterized using spectroscopic techniques like static and time resolved photoluminescence (TRPL) along with X-Ray photoelectron spectroscopy (XPS). Measured lifetime of defects was in several hundreds of pico-second. From the spectroscopic characterizations, anomalous behavior of Mn related defects in the MnZnS thin films were explained. An extensive study on XPS of the prepared MnxZn(1-x)S thin film gave greater insight to the possible mechanism for this anomalous luminescence behavior.

Origin and tunability of dual color emission in highly stable Mn doped CsPbCl3 nanocrystals grown by a solid-state process

Herein, we report on a facile, bulk scale room temperature solid-state synthesis of highly stable and luminescent Mn-doped CsPbCl3 nanocrystal (NCs) with high Mn substitution, and investigate the origin and tunability of its dual-color emission. The structural and compositional analyses confirm the successful doping of Mn (1–40%) ion in CsPbCl3 NCs. The Mn-doped CsPbCl3 NCs exhibit distinct excitonic photoluminescence (PL) emission at ~412 nm (Iex) and Mn related emission at ~590 nm (IMn) with high PL quantum yield (up to 35%). Our study reveals that the intensity ratio IMn/Iex could be widely tuned by a factor of 64 and 23 by changing the Mn concentration and the measurement temperature, respectively. The stronger Mn emission at higher temperature is attributed to the higher rate of transfer of photoexcited carriers from the excitonic state of CsPbCl3 host to Mn related state. Further, excitation intensity-dependent PL along with time-resolved PL studies revealed important insights into the origin and tunability of Mn related orange-red PL in the dual color emitting Mn-doped CsPbCl3 NCs. The PL line shape analysis revealed additional PL peak in the range ~634–666 nm, which grows stronger with higher doping concentration and it is attributed, for the first time, to structural defects in the NCs. Remarkably, the Mn-doped CsPbCl3 NCs synthesized by our method exhibit about 10 times higher storage stability than those reported earlier due to the high Mn doping efficiencies achieved due to the strain induced enhanced doping process. Finally, white light emitting diodes (LEDs) were fabricated by employing blue-emitting CsPbCl1.5Br1.5 NCs, green-emitting CsPbBr3 NCs and orange-red emitting 10% Mn-doped CsPbCl3 NCs all grown by the same method. Our work demonstrates a low-cost synthesis strategy for high Mn doping in CsPbCl3 NCs with superior ambient stability and highly tunable emission.

Tailoring the visible emissions in ZnS:Mn films for white light generation

Abstract This paper reports the effect of manganese incorporation on the structural, optical and luminescence properties of the as-deposited ZnS films prepared by RF magnetron sputtering process. Mn act as a nucleation centre for the growth of highly crystalline defect free ZnS films with mixed cubic and hexagonal phases. The +2 valence state of Mn ions in ZnS lattice is confirmed by the XPS analysis. An absorption band due to d-d transition of Mn2+ ions is visible in the absorption spectra of ZnS film with highest Mn doping concentration. ZnS:Mn films present an intense orange emission along with the host emissions of ZnS. Optimum Mn content for superior orange emission from ZnS:Mn films is found to be 3 wt %. Origin of orange photoluminescence emission due to the incorporation of Mn2+ in Zn2+ host lattice and its quenching due to cross-relaxation mechanism in the films with higher Mn doping concentration is discussed in detail. We report the possibility of one-step generation of white light emission from the as-synthesized ZnS:Mn films by the adequate tailoring of ZnS host emissions in the blue and green regions (445 nm and 530 nm respectively) and Mn related emission in the orange region (585 nm) employing only one excitation wavelength by suitably tuning the Mn doping concentrations. PL decay of the orange emission is monitored to explore the luminescence mechanism and lifetime of the emission.

Correlation between Photoluminescent and Photoelectrical Properties of Mn-Doped ZnO

ZnO ceramics undoped and doped with manganese are investigated. The Mn content NMn is varied from 1019 to 1021 cm−3. The photoluminescence (PL), diffuse reflection, and photoconductivity (PC) spectra are measured. The quenching of the self-activated ZnO emission and the appearance of the light absorption and PC are observed in the same spectral region (400–600 nm) under the doping. Simultaneously, a week PL band peaked at 645 nm arose and was assigned to intra-shell transitions in Mn2+Zn centers. Based on the analysis of obtained results, the quenching effect is attributed to the re-absorption of the self-activated ZnO emission by Mn ions. A scheme of electron transitions that allows an explanation of the low intensity of the Mn-related emission is proposed.

Competition of the self-activated and Mn-related luminescence in ZnS single crystals

The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of ZnS single crystals thermally doped from ZnS/MnS mixture were studied at 300 and 77 K. PL spectra exhibit bands caused by Mn-related centers and centers of self-activated (SA) emission. Besides intrinsic maximum, a number of narrow peaks corresponded to Mn-related absorption are found in the PLE spectra of both SA and Mn-related emission. A redistribution of SA and Mn-related emission intensities is observed with temperature change. The mechanism of this phenomenon involving free hole trapping by MnZn and the possible position of a ground energy level of substitutional Mn are discussed.

Mn-Doped cesium lead halide perovskite nanocrystals with dual-color emission for WLED

CsPbX3 perovskite nanocrystals (NCs) are promising materials for light-emitting optoelectronics, which possess optically tunable bandgap, bright photoluminescence (PL), and excellent photoluminescence quantum yield. However, doping this new class of promising NCs with optically active or magnetic transition metal ions are still limited. Based on the status quo, we synthesized Mn-doped CsPbCl3 and CsPb(Cl/Br)3 NCs by one-pot synthesis method using MnCl2·(H2O)4 as the precursor. The intensity and position of this Mn-related emission are also tunable by altering the experimental parameters, such as reaction temperature and the Pb-to-Mn feed ratio. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX3 NCs, and well-defined electron paramagnetic resonance spectra of Mn2+ in host CsPbX3 NCs lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb2+. In spite of the excellent luminescent properties of Mn-doped CsPbX3 NCs, their instability is still an important issue that obstruct their practical applications. In this paper, we reported a screen printing technology to prepare Mn-doped CsPbCl3 epoxy resin (ER) orange film for enhancing the stability of Mn-doped CsPbCl3 NCs. More importantly is that we fabricated NCs-ER with Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor-in-glass (PiG) realized the chromaticity tuning for YAG:Ce3+ phosphor with white light-emitting-diodes (WLED). In short, warm WLED were constructed by blending the Ce-PiG and orange Mn-doped CsPbCl3-ER materials with the InGaN blue chips.

Low temperature photoluminescence study of Mn-doped ZnSe nanocrystals

In the present work, photoluminescence and photoluminescence excitation (PLE) spectroscopy have been employed to study d-d and p-d exchange interaction of Mn-doped ZnSe nanocrystals (NCs) from room temperature through 10K. Mn-doped ZnSe NCs of size about 5nm with zinc blend crystal structure are grown by the nucleation doping strategy. The doped-NCs reveal strong Mn-related emission; surprisingly that shows red shift with the decrease in temperature. At 10 K, four different excitation features related to d-d transitions of Mn2+ were observed. Crystal field parameter (Dq) and Racah parameters (B and C) are calculated using low temperature PLE spectra recorded by fixing the Mn2+related orange luminescence emission. Increased covalency of the metal-ligand bond and the enhanced exchange interaction between different d-electrons is found. Increment in covalency and exchange interaction is corroborated by the appearance of broad feature in electron spin resonance spectroscopy.

CsPbxMn1-xCl3 Perovskite Quantum Dots with High Mn Substitution Ratio.

CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) are potential emitting materials for illumination and display applications, but toxic Pb is not environment- and user-friendly. In this work, we demonstrate the partial replacement of Pb with Mn through phosphine-free hot-injection preparation of CsPbxMn1-xCl3 QDs in colloidal solution. The Mn substitution ratio is up to 46%, and the as-prepared QDs maintain the tetragonal crystalline structure of the CsPbCl3 host. Meaningfully, Mn substitution greatly enhances the photoluminescence quantum yields of CsPbCl3 from 5 to 54%. The enhanced emission is attributed to the energy transfer of photoinduced excitons from the CsPbCl3 host to the doped Mn, which facilitates exciton recombination via a radiative pathway. The intensity and position of this Mn-related emission are also tunable by altering the experimental parameters, such as reaction temperature and the Pb-to-Mn feed ratio. A light-emitting diode (LED) prototype is further fabricated by employing the as-prepared CsPbxMn1-xCl3 QDs as color conversion materials on a commercially available 365 nm GaN LED chip.

New insight on the interaction of self-activated and Mn-related emission centers in ZnS

The photoluminescence (PL) and PL excitation (PLE) spectra of undoped and thermally doped with Mn ZnS single crystals are studied. In the PL spectra, the bands caused by Mn-related and self-activated (SA) emission centers were observed. A number of narrow peaks whose intensity enhanced with increasing Mn content were found in the PLE spectra of SA emission. The same peaks were present in the PLE spectra of the Mn-related emission band. Some of these peaks were previously observed in the absorption spectra and attributed to Mn2+ ions. The appearance of Mn-related peaks in the PLE spectra of SA emission is explained by excitation transfer from the Mn2+ ions to SA emission centers. The conditions required for this transfer and possible mechanisms of the process are discussed.

Photoluminescence of ZnBeMnSe solid solutions

In this paper optical properties of Zn1-x-yBexMnySe mixed semiconductors were studied as a function of both, temperature and excitation power. The crystals under investigation were grown by the high-pressure, high-temperature vertical Bridgman technique within the range of the composition 0.05≤x, y≤0.2. Photoluminescence spectra for the lowest content of Mn and Be exhibit character typical for II-VI semiconductors together with intensive yellow-orange manganese emission. Evolution of the excitonic emission as the function of temperature allowed determining the energy gap of the investigated semiconductors. Absorbance and photoluminescence excitation spectra confirmed crystal field splitting of excited atomic terms of manganese ions into the states, denoted according to the crystal field theory in the case of tetrahedral symmetry. Temperature and laser power dependences of luminescence showed anomalous behavior of the manganese emission. It turned out that the position of the Mn2+ related luminescence band does not change monotonically with the variation of the temperature or the excitation power. Finally, switching of the manganese emission has been observed. By increasing laser power of exciting radiation, the Mn-related emission could be quenched by almost two orders in magnitude. This effect was especially strong at low temperature and it was fully reversible.

Influence of growth temperature on the morphology and luminescence of Ga2O3:Mn nanowires

Mn doped β‐Ga2O3 nanowires have been obtained by a thermal evaporation method on a gallium oxide substrate. The growth temperature has been varied in the range 1300–1500 °C. The morphology of the resulting structures has been found to depend on this temperature, as observed in the images obtained with scanning electron microscopy. The structures grown on the sample at 1500 °C are both isolated microrods and interconnected rods. At lower temperatures, 1300 and 1400 °C, nanowires with widths of about 100 nm and stair‐shaped microcrystals were found. Raman analysis demonstrates that both nanowires and microrods present the β‐Ga2O3 crystal structure. In addition, Mn related light emission has been found to depend on the growth temperature. The assessment of luminescence properties have been carried out by cathodoluminescence analysis. The results show an intense orange emission in the nanowires and green emission in the microrods. These bands are associated to the manganese ions incorporated into the gallium oxide crystal lattice.

Electrical transport and optical emission of MnxZr1-xO2(≤x≤.5) thin films

Mn x Zr 1 - x O 2 (MnZO) thin films were grown by pulsed-laser deposition on single crystalline yttria-stabilized zirconia (YSZ) and a-plane sapphire substrates with manganese contents from 0 up to about 50 at.%. A fully stabilized cubic structure occurs for Mn contents x equal or larger than 20 at. % on YSZ substrates. For x ≈0.5, phase separation of Mn-oxides occurs. Below 11 at. %, only the monoclinic phase is observed. The thin films are electrically insulating up to x = 0.3. By further increasing the Mn content or by reducing the structural quality, the resistivity ρ decreases from 3×109Ωcm down to 3×104Ωcm. For MnZO thin films on a-plane sapphire substrates, Seebeck-effect measurements verify a transition from p-type conductivity to n-type conductivity around 500 K with increasing temperature, which is probably governed by an enhanced ionic conduction. Cathodoluminescence measurements clearly show a Mn-related emission at about 2.8 eV, correlated to an Mn-induced electronic state in the bandgap of MnZO. From electron paramagnetic resonance measurements and x ray photoelectron spectroscopy, we conclude that both Mn3+ and Mn4+ is present in our MnZO thin films.

Enlarged ferromagnetic hysteresis in InMnP:Be epilayers formed by thermal diffusion using MBE-grown Mn/InP:Be bilayers

The p-type InMnP:Be epilayers, which were prepared by thermal diffusion of Mn through in-situ deposition of Mn layer using molecular beam epitaxy (MBE) onto MBE-grown InP:Be epilayers and subsequent in-situ annealing at 300–350 °C, were investigated. InMnP:Be epilayers prepared by the above sequence clearly showed the Mn-related emission band at 1.1–1.2 eV, which indicates the effective incorporation of Mn 2+ ions into the host layer InP:Be. The samples demonstrated very large ferromagnetic hysteresis loops with enhanced coercivity, and the ferromagnetic-to-paramagnetic transition of the samples was observed to occur at ∼85 K. These results suggest that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be effectively formed by the above-mentioned sequential in-situ processes.

Optical and Structural Properties of Mn-Doped GaN Grown by Metal Organic Chemical Vapour Deposition

Mn-doped GaN epitaxial films were grown by metal organic chemical vapour deposition (MOCVD). Micro-structural properties of films are investigated using Raman scattering. It is found that with increasing Mn-dopants levels, longitudinal optical phonon mode A1 (LO) of films is broadened and shifted towards lower frequency. This phenomenon possibly derives from the difference in bonding strength between Ga-N pairs and Mn-N pairs in host lattice. In addition, optical properties of films are investigated using cathodoluminescence and absorption spectroscopy. Mn-related both emission band around 3.0eV and absorption bands around 1.5 and 2.95eV are observed. By studies on structural and optical properties of Mn-doped GaN, we find that Mn ions substitute for Ga sites in host lattice. However, carrier-mediated ferromagnetic exchange seems unlikely due to deep levels of Mn acceptors.

Luminescence and Absorption Spectroscopy of Weakly Mn-Doped SrTiO3 Crystals

The emission and excitation spectra of photoluminescence of the as-grown and reduced SrTiO 3 :Mn (280 ppm) crystal were studied within wide temperature (12 – 300 K) and spectral (300 – 1600 nm) regions. The emission spectra consist of two overlapping bands. The first one corresponds to the emission of Mn 4 + ions substituted in octahedral coordinated Ti 4+ sites with zero-phonon line peaking at 723.23 nm at 12 K. The second broad emission band peaking near 870 nm was observed on SrTiO3:Mn crystals for the first time. Temperature behavior of photoluminescence intensity and the origin of this new Mn related emission band are discussed.

Time resolved spectroscopic studies on some nanophosphors

Time resolved spectroscopy is an important tool for studying photophysical processes in phosphors. Present work investigates the steady state and time resolved photoluminescence (PL) spectroscopic characteristics of ZnS, ZnO and (Zn, Mg)O nanophosphors both in powder as well as thin film form. Photoluminescence (PL) of ZnS nanophosphors typically exhibit a purple/blue emission peak termed as self activated (SA) luminescence and emission at different wavelengths arising due to dopant impurities e.g. green emission for ZnS: Cu, orange emission for ZnS: Mn and red emission for ZnS: Eu. The lifetimes obtained from decay curves range from ns to ms level and suggest the radiative recombination path involving donor-acceptor pair recombination or internal electronic transitions of the impurity atom. A series of ZnMgO nanophosphor thin films with varied Zn: Mg ratios were prepared by chemical bath deposition. Photoluminescence (PL) excitation and emission spectra exhibit variations with changing Mg ratio. Luminescence lifetime as short as 10−10 s was observed for ZnO and ZnMgO (100: 10) nanophosphors. With increasing Mg ratio, PL decay shifts into microsecond range. ZnO and ZnMgO alloys up to 50% Mg were prepared as powder by solid state mixing and sintering at high temperature in reducing atmosphere. Time resolved decay of PL indicated lifetime in the microsecond time scale. The novelty of the work lies in clear experimental evidence of dopants (Cu, Mn, Eu and Mg) in the decay process and luminescence life times in II–VI semiconductor nanocrystals of ZnS and ZnO. For ZnS, blue self activated luminescence decays faster than Cu and Mn related emission. For undoped ZnO nanocrystals, PL decay is in the nanosecond range whereas with Mg doping the decay becomes much slower in the microsecond range.

Manganese doping and optical properties of ZnS nanoribbons by postannealing

Manganese (Mn) doping of ZnS nanoribbons was achieved by simple thermal annealing. Upon heating ZnS nanoribbons with MnS powder up to 700°C, the intrinsic photoluminescence (PL) of the annealed nanoribbons disappeared and a new PL peak at 585nm gradually emerged. Significantly, the annealing process induced no detectable change in the morphology and uniform hexagonal wurtzite 2H structure of the single-crystal ZnS nanoribbons. The PL peak at 585nm is attributed to Mn dopant and confirms Mn incorporation in ZnS because (1) the peak appears only when ZnS ribbons were annealed with MnS, but does not appear without MnS, (2) its intensity increases with increasing annealing temperature, which is consistent with increased incorporation of Mn2+ ions, and (3) its position is similar to that of Mn-related emission in ZnS, and is independent of the measuring temperature and excitation power. This work demonstrates the capability of doping nanostructured materials by simple postannealing treatment.