Integrated Photoluminescence Intensity Research Articles

Designing a high-efficiency broadband cyan phosphor for low-blue full-spectrum LED lighting

Efficient cyan-emitting phosphor plays an important role in the development of solid-state lighting, which is indispensable to filling the cyan gap for full-spectrum warm-white light-emitting diodes (WLEDs) with high color rendering index (CRI). Herein, a novel highly efficient broadband cyan phosphor Ce3+-doped Ca3HfAl2Si2O12 (CHASO: Ce3+) garnet compound was developed by the substitution of Lu3+-Al3+ with Ca2+-Hf4+/Si4+ in Lu3Al5O12. The crystal structure and photoluminescence (PL) properties of CHASO: Ce3+ were investigated in detail. Notably, CHASO: Ce3+ phosphor can be effectively excited by violet light (390 – 430 nm) and exhibited bright cyan emissions around 490 nm with high PL internal quantum yields of 89.2 %. Moreover, the integrated PL intensity of the phosphor at 423 K was 66.3 % of that at room temperature. Finally, by incorporating CHASO: 11 %Ce3+ with commercial blue/yellow/red phosphor onto a violet LED chip (400 nm), the prototype full-spectrum WLEDs device exhibits warm white light with high color rendering index (CRI, Ra and R9 > 90) and low correlated color temperature 3301 K. These results suggest the highly efficient phosphor CHASO: Ce3+ is promising for low-blue full-spectrum healthy lighting.

Photoluminescence of dense arrays of InGaPAs/InGaAs quantum dots formed by substitution of group V elements

One drawback of self-organized quantum dots is their low optical gain. The development of new shaping methods that would allow higher gain, for example, due to a higher surface density of the QD array, remains an important task to date. In the present work, arrays of quantum dots have been formed by substituting phosphorous atoms with arsenic ones in a thin InGaP epilayer. Based on transmission electron microscopy data, the surface density was estimated to be about 1.3 × 1012 cm−2, which is one of the highest values for quantum dots on GaAs. The influence of an additional InGaAs epilayer (quantum well) on the luminescence properties of quantum dots was investigated in a wide temperature range and different optical pumping levels. It was found that placing the quantum well under the layer of quantum dots has little effect on the central emission wavelength, while quantum dots covered with the InGaAs demonstrate a strong red shift of the luminescence spectrum. A transition from a nonequilibrium to an equilibrium distribution of charge carriers over quantum-dot states, related to the lateral transport of charge carriers over quantum dot array, similar to that previously observed in In(Ga)As Stranski-Krastanow quantum dots, was revealed. This is manifested in a change in temperature dependencies of the linewidth and peak position of the photoluminescence band. For the structures under study, this transition occurs at a temperature of about 125 K. Rapid thermal annealing of the structures allows to increase the integrated photoluminescence intensity of quantum dots up to 4 times, while the maximum of the spectrum remains almost unchanged, provided that the annealing temperature does not exceed 620 °C.

High external quantum yield in near-infrared phosphor Bi2Ga4O9:Cr3+ excited by near-ultraviolet or blue light

The proliferation of portable and intelligent devices featuring Near-Infrared (NIR) light sources as a central component has resulted in a significant need for compact NIR light sources. The technique of NIR phosphor-converted light-emitting diodes (NIR-pc-LEDs) could offer a fresh viewpoint on NIR light sources. The performance of NIR-pc-LEDs is directly influenced by NIR phosphors. However, the development of NIR phosphors with high external quantum yield (EQY) NIR phosphors has been hampered. In this work, we report a mullite-structure NIR phosphor, Bi2Ga4O9: Cr3+ (BGO), which exhibits excellent NIR luminescence properties. The emission spectrum of the optimal doped sample BGO:0.06Cr3+ has two emission peaks at 711 and 763 nm. All samples can be efficiently excited by commercial 365 nm near-ultraviolet LED chips and 450 nm blue LED chips. The internal quantum yield (IQY) reaches an astonishing value of 89.13 % and an EQY of about 65.36 % at 365 nm excitation. Furthermore, BGO:0.06Cr3+ shows a high IQY (∼87.78 %) and EQY (∼41.64 %) upon 450 nm excitation. Moreover, concerning thermal stability, the integrated photoluminescence intensity remains at 82 % and 42 % of that at room temperature when measured at 373 K and 423 K, respectively. The capsuled NIR-pc-LED device can be utilized for blood veins imaging, food safety analysis, and information encryption. These results highlight the promising commercial prospects of BGO:0.06Cr3+ in the fields of bio-imaging and non-destructive testing, among others.

Low-temperature behavior of heat capacity and pho-toluminescence of a binuclear pivalate complex [Eu2(bath)2(piv)6

The low-temperature behavior of the heat capacity and photoluminescence of the previously structurally characterized binuclear pivalate complex [Eu2(bath)2(piv)6] (monoclinic, I2/a) (1), where bath = 4,7-diphenyl-1,10-phenanthroline, piv = (CH3)3CCO2-. Using the adiabatic calorimetry method, the temperature dependence of the heat capacity was measured in the temperature range 5.96–302.88 K and the thermodynamic functions Cp0(T), S0(T), Ф0(Т) and Н0(Т) - Н0(0) were calculated. The absence of low-temperature phase transformations of complex 1 was shown. It was established that in the temperature range 98-295 K, complex 1 demonstrates high temperature stability of the integral intensity of photoluminescence of the transitions of the Eu3+ ion 5D0-7Fj (j = 0.6).

Simultaneous enhancement of red luminescence and thermal stability of a novel red phosphor: A Li+-Eu3+ co-occupied site strategy in BaAl2Ge2O8 lattices

The rapid development of phosphor-converted white light emitting diodes (pc-WLEDs) requires new red phosphors with efficient and thermally stable luminescence for high-quality warm-white lighting. However, it is still a challenge to discover red phosphors with facile synthesis, high internal quantum efficiency (IQE), excellent thermal stability and high color purity. Herein, a novel red-emitting Eu3+ activated barium dialuminum digermanate (BaAl2Ge2O8, BAGO) phosphor showing strong red emission at 610 nm was prepared. The IQE is improved from 32.91% to 78.84% by employing a charge compensation strategy. The lithium-ion co-doped BAGO:Eu3+ phosphor exhibits a nearly twofold increase in integral photoluminescence (PL) intensity and the high color purity reaches 94.17%. Impressively, the PL intensity of the BAGO:Eu3+,Li+ phosphor drops by only 2.6% at 150 °C of that at room temperature. Finally, the pc-WLED using the red BAGO:Eu3+,Li+ phosphor exhibits white light with the chromaticity coordinate of (0.3515, 0.3495), a high color-rendering index of 92 and a low correlated color temperature of 4746 K. All these results manifest that BAGO:Eu3+,Li+ phosphor is a suitable red phosphor for near-ultraviolet (NUV) chip-based pc-WLEDs.

Optical signatures of suppressed carrier localization in encapsulated WSe2 monolayer

Low carrier mobility, closely associated with the formation of localized states, is the major bottleneck of utilizing the unique quantum transport properties in transition metal dichalcogenides (TMDCs). Here, we demonstrate an effective method to quantify the localization energy based on the temperature-dependent spectral variation of photoluminescence (PL) in pristine and hexagonal boron nitride (h-BN) encapsulated monolayer (ML) WSe2. Considering the protecting capability of h-BN against contamination and degradation, while not affecting the electronic structure as an insulating dielectric, the localization energy was comparatively extracted out of PL spectra in pristine and encapsulated ML WSe2. In pristine ML WSe2, two distinctive energy traces were resolved with an energy difference of about 17 meV, which was associated with the localized state revealed below 200 K. Clear evidence for the carrier localization was also evident in the integrated PL intensity trace with temperature as the trace from pristine ML clearly deviates from the dark-exciton-like behavior of ML WSe2, violating the spin selection rule of the lowest exciton state. In clear contrast, the temperature dependency of the h-BN encapsulated ML WSe2 in PL spectra matches well with the typical Varshni formula of free excitonic peaks and the integrated intensity trace of thermally populated spin subbands. Our study suggests that the h-BN encapsulation could suppress the carrier localization channels by avoiding surface oxidation due to air exposure and could provide insights into how one could preserve the excitonic features in TMDC materials and devices.

Ligand field luminescence in the honeycomb Mott insulator α-RuCl3

Novel electronic structure is central to Kitaev-like quantum spin liquid ground state in the van der Waals antiferromagnet α-RuCl3. In this octahedral low-spin system, the rich bandstructure includes Mott–Hubbard insulating bandgap of ∼1.1 eV and ligand field induced gap of ∼2 eV. Though the bandgap is extensively reported in previous optical and photoemission studies, the latter gap is less understood. In this regard, we probed the ligand field-induced electronic structure of bulk α-RuCl3 single crystals via unpolarized photoluminescence (PL) spectroscopy under linearly polarized excitation in the visible region. We observed the broad principal PL peak at E PL 1.87 eV, close to the energy required for the optical transition across the ligand field splitting gap (∼2 eV). This gap (E PL) monotonically increases with temperature, described by the thermal expansion of lattice parameters dominating the electron–phonon interaction in this Honeycomb Mott insulator. Moreover, we observed the multiplet structure of the PL spectra, which can be explained by parity-forbidden d–d transitions in the light of single ion ligand-field theory. We attribute the broad PL linewidths to strong vibronic coupling modeled by the Huang–Rhys parameter. Further we observed the signature of structural transitions, indicated by thermal hysteresis in normalized integrated PL intensity.

Synthesis and optical properties of highly efficient Na3KMg7(PO4)6:Eu2+ blue phosphor for full-spectrum white-light-emitting diodes: The role of Li2CO3 flux

Full-spectrum phosphor-converted white-light-emitting diodes (pc-WLED) are emerging as a mainstream technology in semiconductor lighting. Nevertheless, high-performance blue phosphor which can be excited efficiently by a 400 nm NUV diode chip is still lacking. Herein, we present a blue-emitting Na3KMg7(PO4)6:Eu2+ phosphor synthesized by the solid-reaction method. Particularly, we find that the using of Li2CO3 as flux can significantly improve the crystal quality and thus the emission efficiency of the phosphor. Meanwhile, the excitation peak of the phosphor shifts from 365 to 400 nm, which is pivotal for efficient NUV (400 nm) diode chip excitation. The practical Eu2+ concentration is also enhanced by using Li2CO3 as flux, and the absorption efficiency is greatly increased. This phosphor exhibits superior PL thermal stability, namely retains 94% integrated photoluminescence intensity at 150 °C of that at 25 °C. As a result, the optimized phosphor shows an emission band peaked at 437 nm with a bandwidth of 40 nm and a high external photoluminescence quantum yield of 51.7%. Finally, a pc-WLED was fabricated by using NKMPO:Eu2+ blue, Sr2SiO4:Eu2+ green, CaAlSiN3:Eu2+ red phosphors, and a 400 nm NUV diode chip. It shows a high color rendering index of Ra = 96.4 and a correlated color temperature of 4358 K. These results prove that NKMPO:Eu2+ is a promising blue phosphor for full-spectrum WLED based on NUV diode chips.

Achievement of full-visible-spectrum lighting in Bi3+-activated strontium gallates via lattice site occupancy engineering toward WLEDs applications

Achieving full-visible-spectrum lighting in a single component is highly desired but still challenging for high-quality phosphor-converted white light emitting diodes (pc-WLEDs). Herein, a broadband emission of Sr3Ga4O9: Bi3+, Yb3+ phosphor covering full-visible-spectrum from 400 to 800 nm is explored via the lattice site occupancy engineering strategy. The Bi3+ singly doped Sr3Ga4O9 phosphor exhibits warm yellow emission for the 3P1→1S0 transition of Bi3+ at Sr1 and Sr3 sites. While the introduction of Yb3+ contributes to the emerge of an extra blue emission band at 445 nm accompanied with a significant enhancement of the integral photoluminescence intensity. It is demonstrated that the chemical substitution of Yb3+ into Sr sites induces the lattice disorder and the increased concentration of Sr vacancies, and the local chemical environment change dominates the occupation of Bi3+ into Sr2 sites, resulting in the remarkable blue emission. Moreover, the WLED device as-fabricated by combining the broadband cyan-emitting Sr3Ga4O9: Bi3+, Yb3+ and the red-emitting CaAlSiN3: Eu2+ phosphors exhibits a high color-rendering index (CRI) of 89.6 and a correlated color temperature (CCT) of 5382 K. This work provides a feasible strategy for regulating the Bi3+occupation in Sr3Ga4O9 matrix and boosts the photoluminescence performance of the corresponding phosphor with broadband emission covering the full visible spectrum.

Growth of GaN Hexagonal Arrays on Partially Crystallized Sapphire Nanomembranes for Micro-Light-Emitting Diodes

100-nm-thick hexagonal fully and partially crystallized sapphire nanomembrane arrays were demonstrated as growth templates for hexagonal micro-sized GaN arrays for micro-light-emitting diodes (LEDs). By simply controlling the thermal treatment time for crystallization of the amorphous membrane, the partially crystallized nanomembrane which has both single- and polycrystalline alumina on the top surface was fabricated. The unique crystalline structures contributed to unique growth behavior which contains selective and lateral overgrowth of GaN, compared to that of GaN on fully crystallized sapphire nanomembranes, leading to superior structural and optical properties of GaN. Threading dislocation densities were reduced by 75% and 1.29 times higher integrated photoluminescence intensity was achieved compared to GaN on the fully crystallized sapphire nanomembranes. Stress in GaN was also fully relaxed due to the ultrathin membrane structure as a compliant substrate. The superior properties of GaN as well as the truncated inverted pyramid structure are expected to improve the performance of micro-LED devices. Hexagonal partially crystallized sapphire nanomembrane technology also provided advances in the fundamental study of epitaxial growth of GaN-based materials.

Photoluminescence characterization of GeSn prepared by rapid melting growth method

In this work, single crystalline GeSn on insulator (GSOI) were grown by rapid melting growth (RMG). The Sn content distribution along the strip was investigated, reaching to 7.8% near the end of the strip. The GeSn strip had high quality with no threading dislocations, as revealed by cross-sectional transmission electron microscopy (XTEM). Photoluminescence (PL) measurements along the strip were performed to check the indirect-direct bandgap transition Sn content of GeSn alloys. It was found the integrated PL intensity increased about 6.6 times for Sn content 0.86%–7.8%. For GeSn with Sn content 6.1%, the temperature-dependent PL shows that the energy difference between direct Γ-Γ valley and indirect L-Γ valley decreases due to the bandgap narrowing (BGN) effect, and the direct band transition gradually dominates the PL spectra as temperature increases. The temperature-dependent PL spectra have only one peak for GeSn with Sn content 7.8%, suggesting the direct bandgap property. These results indicate that GeSn grown by RMG is very promising for fabricating efficient Si based light sources.

Photoluminescence Properties of InAs Quantum Dots Overgrown by a Low-Temperature GaAs Layer under Different Arsenic Pressures

We studied the influence of the arsenic pressure during low-temperature GaAs overgrowth of InAs quantum dots on their optical properties. In the photoluminescence spectrum of quantum dots overgrown at a high arsenic pressure, we observed a single broad line corresponding to unimodal size distribution of quantum dots. Meanwhile, two distinct peaks (~1080 and ~1150 nm) at larger wavelengths are found in the spectra of samples with quantum dots overgrown at a low arsenic pressure. We attributed this phenomenon to the high-pressure suppression of atom diffusion between InAs islands at the overgrowth stage, which makes it possible to preserve the initial unimodal size distribution of quantum dots. The same overgrowth of quantum dots at the low arsenic pressure induces intensive mass transfer, which leads to the formation of arrays of quantum dots with larger sizes. Integrated photoluminescence intensity at 300 K is found to be lower for quantum dots overgrown at the higher arsenic pressure. However, a difference in the photoluminescence intensity for the high- and low-pressure overgrowths is not so significant for a temperature of 77 K. This indicates that excess arsenic incorporates into the capping layer at high arsenic pressures and creates numerous nonradiative recombination centers, diminishing the photoluminescence intensity.

An explanation for the non-monotonic temperature dependence of the photoluminescence spectral features of self-organized InAs QDs

Temperature-dependent photoluminescence (PL) measurements under different excitation densities were performed on self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy. Non-monotonic evolutions in the curves of the PL spectral parameters as a function of the sample temperature were observed in the low-temperature regime. Indeed, the PL peak energy of the QDs shows a sigmoidal variation with increasing temperature. This component is accompanied by an anomalous increase in the integrated intensity over the temperature range of 8–50K. These behaviors have been attributed to the optical emission from deep states that exist in the potential of the dots. A simple rate equation model, which describes the thermally activated emission and trapping of photo-injected carriers, is proposed to illustrate the interpretations made regarding the evolution of the integrated PL intensity with increasing temperature. A good agreement between the model simulation and the PL data was obtained for temperatures ranging from 8 to 300K. It was found that the thermally activated process of the intra-dot redistribution of carriers provides a good description of the anomalous behaviors encountered in the PL investigations depending on the temperature of the QD sample.

Controlling the photoluminescence of quantum emitters in hexagonal boron nitride by external magnetic fields

The recent observation of room temperature spin-dependent photoluminescence (PL) emission from hexagonal boron nitride’s (h-BN’s) defect centers motivates for performing a complementary low-temperature photophysical study of quantum emitters under relatively high magnetic fields. Here, we investigate the PL emission dynamics of h-BN’s visible single-photon emitters under an applied out-of-plane magnetic field at cryogenic temperatures. The PL intensity of the emitters in our work strikingly exhibits strong magnetic field dependence and decreases with the increased magnetic field. A substantial decrease in the integrated PL intensity of the emitters by up to one order of magnitude was observed when the applied field is increased from 0 T to 7 T. The observed reversible photodarkening of PL emission due to the applied magnetic field is in very well agreement with the predictions of a recent joint experimental and theoretical study and can happen only if the spin-selective, non-radiative, and asymmetric intersystem crossing transitions proceed from the triplet excited state to the lowest-lying spin-singlet metastable state and from the metastable state to the triplet ground state. Our results not only shed more light on the light emission paths of defect centers in h-BN but also show the use of the magnetic field as an efficient control knob in the development of magneto-optical devices.

(Digital Presentation) Characterization of Light Emission Properties of Impurity Doped Ge/Si Core–Shell Quantum Dots

Si–based quantum dots (QDs) have attracted much attention as an active element in Si-based optoelectronic applications because their light emission properties due to carrier confinement have potential to combine photonic processing with electronic processing on a single chip. We have focused on CVD formation and characterization of Si-QDs with Ge core and reported their photoluminescence (PL) properties attributable to type II energy-band alignment between the Ge–core and the Si-shell [1-2]. In addition, we have also demonstrated stable electroluminescence in the near–infrared region from diode structures having a 3–fold stacked Si–QDs with Ge core with an areal dot density of ~2.0×1011 cm−2 under pulsed bias applications [3]. One of the possible ways to enhance the radiative recombination rate and the improve the light emission efficiency is to reduce non–radiative centers and to increase carrier density by impurity doping into the QDs. In this work, in extending our research work to valency-controlled Si–QDs with Ge core, we have studied the effects of boron– and phosphorus–doping to the Ge core on PL properties.A highly dense layer of Si–QDs with Ge core was formed by controlling thermal decomposition of GeH4 and SiH4 alternately on thermally–grown ~2.0 nm–thick SiO2. During the Ge deposition, delta doping of boron and phosphorus atoms in QDs was carried out by pulse injection using 1% B2H6 and 1% PH3 diluted with He, respectively. No changes in dot size and areal dot density with B or P doping were confirmed by AFM topographic images. Under photoexcitation of undoped QDs with a 979–nm line from a semiconductor laser, a broad PL spectrum, which consists of four Gaussian components originating from radiative recombination through quantized states in QDs, were observed in the energy range from 0.62 to 0.85 eV even at room temperature. For the doped QDs, in addition to the four components seen in undoped QDs, relatively-narrow components peaked at ~0.64 eV and ~0.68eV were observed with B-doping and with P-doping to the Ge core, respectively. Notice that, with an increase in B2H6 pulse injection from 1 to 4 times, the integrated PL intensity was enhanced by a factor of 1.4 to 2.4 compared to that of the undoped QDs while no significant change in spectral shape was observable. This can be interpreted in terms of an increase in the number of holes with B-doping to the Ge core since the carrier recombination rates is proportional to the product of the number of electrons and holes confined in each of QDs under weak photoexcitation.AcknowledgementsThe authors wish to thank Dr. Akio Ohta for his contribution to the measurements. This work was supported in part by Grant–in–Aid for Scientific Research (A) 19H00762, 21H04559, and Fund for the Promotion of Joint Intentional Research [Fostering Joint International Research (A)] 18KK0409 of MEXT Japan.

K2SiF6:Mn4+ significantly improves water resistance and luminescence performance by coating green emission graphene quantum dots

In order to enhance the luminescent thermal stability and water resistance of K2SiF6:Mn4+, we proposed a simple hydrothermal method to synthesize K2SiF6:0.06Mn4+@GE-GQDS (6 mg/mol) (GE-GQDs: green emission graphene quantum dots) red emitting phosphor with outstanding water resistance. The emission intensity of the sample coated with the GE-GQDs still maintains 87.74% of the initial one after immersion for 360 min, while the uncoated K2SiF6:0.06Mn4+ sharply decreases to 11.26%. Another impressive phenomenon is that due to the negative thermal quenching (NTQ) effect, the luminescent thermal stability of the coated sample is also significantly improved, and the integrated photoluminescence (PL) intensity at 180 °C is 238% of that at 25 °C. In the meantime, the integrated PL intensity of the coated samples is 2.55 times that of K2SiF6:0.06Mn4+ under room temperature. Based on experimental results, it is suggested that after coating with GE-GQDs, a surface protective layer is formed on the surface of the sample, which improves the water resistance, room temperature emission intensity, and luminescent thermal stability of the coated sample. Finally, the improvement mechanism of the above multiple enhancements on luminescent properties is discussed and proposed. The above multiple enhancement effects make the sample have broad application for blue light-based warm and high-power WLEDs (white light-emitting diodes).

Structural and optical investigations on LaGaO3 synthesis by sol–gel method along with a blue luminescence property

• LaGaO 3 perovoskite material has been successfully synthesized by a simple rout called sol gel method. • The efficiency of sol–gel methods to obtain pure phase of LaGaO3 was proved. • Raman reveals 9 bands that correspond to active optical-vibrational modes of orthorhombic symmetry that is in good agreement with XRD results. • A special emphasis is put on the photoluminescence properties of this material. Temperature-dependent PL, low-temperature analysis has been carried out. This work presents the preparation of Lanthanum Gallate peroveskite (LaGaO3) by sol–gel based Pechini method at low temperatures. The structural and optical properties of the elaborated material were investigated, by means of X-ray diffraction (XRD), Raman, UV–visible and Photoluminescence (PL) Spectroscopies. The XRD pattern showed a pure orthorhombic phase of LaGaO3 annealed at 600 °C. The orthorhombic symmetry was confirmed by Raman study. The band gap energy was estimated from UV–visible diffuse reflectance spectra to be 3.64 eV. Photoluminescence spectra of LaGaO3 showed two bands in blue region. For a complete understanding of the luminescence properties, a temperature-dependent PL analysis was studied. The temperature dependence for LaGaO3 sample revealed an S-shape behavior. The S-shape phenomenon and the variation of the FWHM values as a function of temperature were discussed. Finally, the thermal activation energy was calculated from the integrated PL intensity as a function of inverse temperature in orders to determinate the thermal stability of material.

Interaction of Ge(Si) Self-Assembled Nanoislands with Different Modes of Two-Dimensional Photonic Crystal.

The interaction of Ge(Si)/SOI self-assembled nanoislands with modes of photonic crystal slabs (PCS) with a hexagonal lattice is studied in detail. Appropriate selection of the PCS parameters and conditions for collecting the photoluminescence (PL) signal allowed to distinguish the PCS modes of different physical nature, particularly the radiative modes and modes associated to the bound states in the continuum (BIC). It is shown that the radiative modes with relatively low Q-factors could provide a increase greater than an order of magnitude in the integrated PL intensity in the wavelength range of 1.3–1.55 µm compared to the area outside of PCS at room temperature. At the same time, the interaction of Ge(Si) islands emission with the BIC-related modes provides the peak PL intensity increase of more than two orders of magnitude. The experimentally measured Q-factor of the PL line associated with the symmetry-protected BIC mode reaches the value of 2600.

Exciton dynamics and photoresponse behavior of the in situ annealed CsSnBr3 perovskite films synthesized by thermal evaporation

The CsSnBr3 photodetectors are fabricated by thermal evaporation and 75 °C in situ annealing, and the effect of in situ annealing on the morphology, structure, exciton dynamics and photoresponse of thermally evaporated CsSnBr3 films are investigated. Especially, temperature dependent steady-state photoluminescence (PL) and transient PL decaying have been analyzed in details for understanding the exciton dynamics. Meanwhile, effect of annealing on the activation energy for trap sites (E a), exciton binding energy (E b), activation energy for interfacial trapped carriers (ΔE), trap densities and carriers mobilities are studied and the annealed (A-CsSnBr3) reveals obviously lower E b and trap density together with notably higher carrier mobility than those of the unannealed (UA-CsSnBr3). Temperature dependence of the integrated PL intensity can be ascribed to the combining effect of the exciton dissociation, exciton quenching through trap sites and thermal activation of trapped carriers. The temperature dependent transient PL decaying analysis indicates that the PL decaying mechanism at low and high temperature is totally different from that in intermediate temperature range, in which combing effect of free exciton and localized state exciton decaying prevail. The beneficial effects of the in situ annealing on the photoresponse performance of the CsSnBr3 films can be demonstrated by the remarkable enhancement of the optimal responsivity (R) after in situ annealing which increases from less than 1 A W−1 to 1350 A W−1 as well as dramatically improved noise equivalent power, specific detectivity D* and Gain (G).

Highly improved optical properties of silicon nanowires by deposition of Poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] polymer

This paper reports on the effect of the Poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) deposition on the chemical composition and the optical properties of silicon nanowires (SiNWs). The SiNWs were obtained by a single-step Ag-assisted chemical etching method, and then coated by MEH-PPV polymer using the electroless dipping method. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transformed Infra-Red (FTIR) spectroscopy were used to probe the deposition of the polymer on the SiNWs surface and its chemical interaction with them. The optical properties of the elaborated samples were investigated by photoluminescence (PL) spectroscopy. The PL spectra show that the PL emission range of the nanowires is practically the same as that of the MEH-PPV. We also get an enhancement of five orders of the integrated PL intensity of MEH-PPV/SiNWs sample compared to that of untreated SiNWs sample. The PL intensity enhancement is attributed to the luminescent centers of MEH-PPV molecules as well as the passivation of silicon nanowires surface. Interchain and intrachain transitions in the polymeric layer as well as the carriers transfer between SiNWs and MEH-PPV are the main sources of the multiband PL spectra.