Nanosecond Pulse Excitation Research Articles

The plasma reforming of methane in rocket engines under multiple working conditions and its effect on ignition delay

The dielectric barrier discharge (DBD) plasma reforming of methane is ideal for fuel upgrading in rocket engine. However, the working conditions such as high flow rate, high pressure, and low temperature in the propellant supply system significantly affect the reforming performance. This research explores the performance of plasma methane reforming under extreme conditions, examining the characteristics of four kinds of structures, with aims to make reasonable engine design and settings based on actual needs. Simulation is conducted to investigate the effect of plasma reforming on methane ignition delay. The results indicate that prolonging the gas residence could promote methane decomposition. The methane conversion rate under Nanosecond pulsed (NP) excitation is 9.6% higher than that under AC excitation, and the energy utilization efficiency is 1.8% higher. However, the carbon deposition of NP excitation is more severe. As the pressure increases, the cracking reaction intensity decreases by 5%. NP excitation has ideal adaptability to high work pressure. Low temperature has little effect on methane plasma conversion but could affect product distribution, promoting the transformation towards H2 and C2H6. The ignition delay could be shortened by 71 ms with C3H8 adding. The results of this study provide theoretical guidance for the ignition improving of the rocket engine.

High-spatiotemporal resolution microwave-induced thermoacoustic tomography for imaging biological dynamics in deep tissue

Biological systems undergo constant dynamic changes across various spatial and temporal scales. To investigate the intricate biological dynamics in living organisms, there is a strong need for high-speed and high-resolution imaging capabilities with significant imaging depth. In this work, we present high-spatiotemporal resolution microwave-induced thermoacoustic tomography (HR-MTAT) as a method for imaging biological dynamics in deep tissues. HR-MTAT utilizes nanosecond pulsed microwave excitation and ultrasound detection, with appropriate spatial configurations, to achieve high coupling of the sample to the microwaves, to produce images in soft tissue with dielectric contrast and sub-millimeter spatial resolution (230 μm), to a depth of a few centimeters. Notably, by employing a 128-channel parallel signal acquisition and digitization strategy, the field programmable gate array module manages data synthesis, and GPU-based parallel pixel reconstruction facilitates HR-MTAT to accomplish single-frame image reconstruction in an impressive 50 μs. The practical feasibility of HR-MTAT was evaluated in live mice. The results show that HR-MTAT can noninvasively image whole-body small animals (up to 60 mm in depth) with clear resolution of internal organ structures at a frame rate of 100 Hz, without the need for labeling. At this high spatiotemporal resolution, HR-MTAT can capture respiration, heartbeat, and arterial pulse propagation without motion artifacts and track bio-nanoprobes in livers and tumors. These findings demonstrate HR-MTAT's ability to perform dynamic imaging with high contrast and resolution in deep tissues.

The Influence of Concentrations of Sensitizers and Activators on Luminescence Kinetics Parameters of Up-Conversion Nanocomplexes NaYF4:Yb3+/Tm3+

For colloids of NaYF4:Yb3+/Tm3+ nanoparticles in DMSO, by the method of time-resolved luminescence spectroscopy with nanosecond pulsed excitation at a wavelength of 975 nm, the photophysical processes that determine the course of kinetic curves have been revealed. It has been found that the luminescence rise time decreases with an increase in the concentration of activators and sensitizers due to the increase in the efficiency of energy transfer from sensitizers to activators. The cross-relaxation of the excited states of activators provides a decrease in the luminescence decay time with an increase in the concentration of activators and a constant concentration of the sensitizer. There is no correlation between the time of luminescence decay with the change in the concentration of sensitizers and the constant concentration of activators due to the competition of the processes of energy back transfer from activators to sensitizers and the “feeding” of activators by excitations coming from remote sensitizer ions.

Nanobelt and nanoplatelet structured molybdenum disulfide thin film as a saturable absorber under nanopulsed green laser excitation

Demonstration of saturable absorption (SA) in MoS2 thin films with varying NLO coefficients as a function of reaction time of hydrothermal method is made using the open aperture Z-scan technique. Under nanosecond pulsed laser excitation (532 ​nm, 9 ns, 10 HZ), saturable absorption occurred involving the overtone of electron - hole pair state and band edge state of MoS2. Further higher ground state cross-section than excited state cross-section favors SA process in MoS2 thin films. The strong saturable absorption behaviors of nanobelt like structured MoS2 film could be attributed to the coexistence of 1T and 2H crystal phases and lower dimension morphology that allows more photons to transit to the higher energy state. Earlier the fabrication of MoS2 thin film on a FTO substrate with a varying reaction time of the hydrothermal technique such as 24, 36, 48 and 60 ​h was made. Raman spectrum has two sets of characteristics vibration representing the metallic 1T – octahedral coordination Oh phase and the semiconducting 2H – trigonal prismatic D3h phase. XRD and Raman studies confirm the formation of mixed phases of MoS2 with 1T phase dominating over 2H phase in MoS2 thin films. Here the absorbance and band gap of the MoS2 thin film increased with increase in reaction time. The luminescence spectra exhibit prominent peaks at 594 ​nm and 621 ​nm resulting from a direct bandgap transition and they are mostly due to the VBM splitting at the K-point. All the films exhibit maximum absorbance in the UV region (291 ​nm) due to the excitonic features of MoS2 and notable absorbance in the visible region (680 ​nm) due to the overtones of MoS2 ‘s electron-hole pair. SEM images confirm that nanoplatelet and nanobelt structured MoS2 was formed with varying size with respect to reaction time. Furthermore, while the nanoplatelet structure faded, nanobelts were grown for a prolonged reaction time. Thus, MoS2 nanostructure coated thin film would be useful for the design of saturable absorbers for fabricating optical switches and mode locking devices.

Quantum dot lasing from a waterproof and stretchable polymer film

Colloidal quantum dots (QDs) are excellent optical gain materials that combine high material gain, a strong absorption of pump light, stability under strong light exposure and a suitability for solution-based processing. The integration of QDs in laser cavities that fully exploit the potential of these emerging optical materials remains, however, a challenge. In this work, we report on a vertical cavity surface emitting laser, which consists of a thin film of QDs embedded between two layers of polymerized chiral liquid crystal. Forward directed, circularly polarized defect mode lasing under nanosecond-pulsed excitation is demonstrated within the photonic band gap of the chiral liquid crystal. Stable and long-term narrow-linewidth lasing of an exfoliated free-standing, flexible film under water is obtained at room temperature. Moreover, we show that the lasing wavelength of this flexible cavity shifts under influence of pressure, strain or temperature. As such, the combination of solution processable and stable inorganic QDs with high chiral liquid crystal reflectivity and effective polymer encapsulation leads to a flexible device with long operational lifetime, that can be immersed in different protic solvents to act as a sensor.

Ultrasonication assisted exfoliation of MoSe2 nanosheets for optical and optical power limiting applications

We report direct, economic, and facile preparation of two-dimensional transition metal dichalcogenide material molybdenum diselenide nanosheets through the ultrasonication assisted liquid exfoliation method. The optical absorption spectra confirm the formation of MoSe2 nanosheets. The Kramers–Kronig expression was used to estimate the refractive index and extinction coefficient values of the prepared nanosheets. The emission properties of the prepared samples were done using photoluminescence spectroscopy. The nonlinear optical studies were performed using an open aperture Z-scan method under nanosecond pulsed laser excitation of a second harmonic generation wavelength of 532 nm. The obtained results demonstrate the strong optical power limiting (OPL) properties of the MoSe2 nanosheets. This OPL is due to two-photon absorption behavior of MoSe2 nanosheets.

Ultra-Broadband Random Laser and White-Light Emissive Carbon Dots/Crystal In-Situ Hybrids.

The continuous white-light emission of carbon dots (CDs) can be applied to producing multicolor laser emissions by one single medium. Meanwhile, the solid-state emission greatly contributes to its practical application. In this work, a strategy to realize the in-situ hybridization of silane-functionalized CDs (SiCDs) and 1,3,5-benzenetricarboxylic acid trimethyl ester (Et3BTC) by a one-pot solvothermal method is reported. Significantly, the SiCDs/Et3BTC hybrid crystals exhibit ultra-broadband random laser emission over the near ultraviolet-visible region under 265nm nanosecond pulsed laser excitation. The wavelength region of laser emission is achieved from 315 to 600nm within an emission band of CDs-based materials. It is worth noting that the wavelength range of the laser is wider than the previously reported works. It is proposed that the continuous white-light emission of SiCDs caused by multiple fluorescence centers mainly gives rise to the broadband random laser emission. Moreover, the crystals are conducive to forming resonance and realizing solid-state laser emission. This in-situ method is expected to enable a more convenient, cheaper, and greener approach to prepare luminescent hybrids for application in multicolor laser displays, multi-level laser anti-counterfeiting, supercontinuum light sources, and so on.

MAPbBr3 First‐Order Distributed Feedback Laser with High Stability

A green‐emitting perovskite first‐order distributed feedback (DFB) laser based on the methylammonium lead bromide (MAPbBr3) with high stability is demonstrated for the first time. The laser achieves stable lasing at 550 nm with a full width at half maximum of 0.4 nm. Low lasing threshold of 60 μJ cm−2 under nanosecond pulsed excitation and 3.1 μJ cm−2 under femtosecond pulsed excitation is observed, showing a much lower lasing threshold compared with the second‐order DFB cavities, which are fabricated on the same substrate. By optimizing the antisolvent treatment and encapsulating with poly(methyl methacrylate), the laser lifetime, resistance to moisture, lasing threshold, and intensity are significantly improved. The lasers are fabricated with a complementary metal‐oxide‐semiconductor‐compatible process, thus offer promising potential for the integrated photonic devices.

Optical Properties and Upconversion Luminescence of BaTiO3 Xerogel Structures Doped with Erbium and Ytterbium

Erbium upconversion (UC) photoluminescence (PL) from sol-gel derived barium titanate (BaTiO3:Er) xerogel structures fabricated on silicon, glass or fused silica substrates has been studied. Under continuous-wave excitation at 980 nm and nanosecond pulsed excitation at 980 and 1540 nm, the fabricated structures demonstrate room temperature PL with several bands at 410, 523, 546, 658, 800 and 830 nm, corresponding to the 2H9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2→ 4I15/2 and 4I9/2→ 4I15/2 transitions of Er3+ ions. The intensity of erbium UC PL increases when an additional macroporous layer of strontium titanate is used beneath the BaTiO3 xerogel layer. It is also enhanced in BaTiO3 xerogel films codoped with erbium and ytterbium (BaTiO3:(Er,Yb)). For the latter, a redistribution of the intensity of the PL bands is observed depending on the excitation conditions. A multilayer BaTiO3:(Er,Yb)/SiO2 microcavity structure was formed on a fused silica substrate with a cavity mode in the range of 650–680 nm corresponding to one of the UC PL bands of Er3+ ions. The obtained cavity structure annealed at 450 °C provides tuning of the cavity mode by 10 nm in the temperature range from 20 °C to 130 °C. Photonic application of BaTiO3 xerogel structures doped with lanthanides is discussed.

All-optical laser ultrasonic technique for imaging of subsurface defects in carbon fiber reinforced polymer (CFRP) using an optical microphone

Defects, such as delamination and debonding, are critical to the performance of carbon fiber-reinforced polymer (CFRP) composites. In recent years, non-destructive testing techniques have been improved for the inspection of these defects among CFRPs. In this study, an all-optical and non-destructive laser ultrasonic technique with an optical microphone detection module has been presented to detect the artificial subsurface defects among the CFRP composites. A finite element simulation based on the thermo-mechanical coupling model was used to study the process of nanosecond pulsed laser excitation of the CFRP laminate to produce ultrasound and the propagation behavior of ultrasound among the CFRP laminate. A series of non-contact laser ultrasonic testing experiments were carried out to study the flat bottom holes of different sizes via a laser ultrasonic detection system. The artificial subsurface defects were reliably identified by the presented all-optical laser ultrasonic system imbedded in the optical microphone using four feature images.

A red-green photochromic bacterial protein as a new contrast agent for improved photoacoustic imaging

The GAF3 domain of the cyanobacteriochrome Slr1393 from Synechocystis sp. PCC6803, binding phycocyanobilin as a chromophore, shows photochromicity between two stable, green- and red-absorbing states, characterized by relatively high photoconversion yields. Using nanosecond-pulsed excitation by red or green light, respectively, and suitable cw photoconversion beams, we demonstrate that the light-modulatable photoacoustic waveforms arising from GAF3 can be easily distinguished from background signals originating from non-modulatable competitive absorbers and scattering media. It is demonstrated that this effect can be exploited to identify the position of the photochromic molecule by using as a phantom a cylindrical capillary tube filled with either a GAF3 solution or with an E.coli suspension overexpressing GAF3. These properties identify the high potential of GAF3 to be included in the palette of genetically encoded photochromic probes for photoacoustic imaging.

Speciation in nanosecond laser ablation of zinc in water

In situ experimental methods have been applied to resolve mass flow and chemical speciation in the pulsed laser ablation of zinc in water. The chemical speciation has been resolved by time-resolved μ-X-ray absorption spectroscopy and mapped onto the macroscopic mass flow during material ejection from the metallic target and bubble dynamics of evaporated water. Large particles and agglomerates have been detected via dark-field X-ray imaging with a Shack-Hartmann sensor. The characteristic of the dynamics is that the vapor bubble is nearly homogeneously filled with ablated material. This persists during bubble collapse, which means that the ablated particles are captured and retracted towards the target. Limited mass escape is indicated by the X-ray absorption signal. Importantly, the near-edge structure at the Zn-Kα transition delivers information on the chemical state of the ejected material. It clearly confirms that oxidation is not present within the bubble phase and the following sub-millisecond time scale. The oxidation proceeds on Zn nanoparticles in suspension on a second to minute course. Within the first microseconds, a Zn atom phase is detected that resembles Zn vapor. The addition of either reductive NaBH4 or oxidative HAuCl4 to the water phase influences the quantity of the atom contribution moderately, but does not influence the initial atom phase. Such behavior must be understood in terms of the nanosecond pulse excitation. After ejected material and a plasma is formed within the pulse duration of 7 ns the laser is able to further heat the ejecta and transform it partly into vapor. Correspondingly, the coupling of energy into the ablation zone as followed by plasma intensity and bubble size follows a threshold behavior as a function of laser fluence, marking the onset of laser-plasma heating. The reaction conditions inside the bubble are probably reductive due to the concomitant formation of excess hydrogen.

Is an extended barrier-free discharge under nanosecond-pulse excitation really diffuse?

A homogeneous discharge with a large volume is a desirable plasma source for many applications. Nanosecond-pulsed high-voltage (HV) excitation is believed to be a promising strategy for obtaining homogeneous or diffuse discharges at atmospheric pressure. In this paper, using a knife–plate geometry driven by a nanosecond-pulsed generator, a diffuse plasma sheet with a gap distance of 1 cm and a length of 12 cm is generated in atmospheric air, maintaining a low gas temperature of ∼330 K. However, time-resolved images reveal that the discharge, which appears diffuse to the naked eye, actually consists of multiple individual streamers that propagate from knife (HV) to plate (ground). The appearance of two processes, namely primary and secondary streamers, is consistently verified by discharge images, electric field evolution and fluid simulation. This further proves that the entire discharge belongs to an intermediate state between corona and spark. This work aids a deeper understanding of the intrinsic characters of similar diffuse discharges and optimizing parameters in practical applications.

Nonlinear optical characteristics of non-covalently functionalised graphene-pyrene-conjugated phthalocyanine hybrids

Improving the non-linear absorption properties of graphene materials is valuable for optical limiting applications. We report the non-linear optical characteristics of new hybrid materials formed by the non-covalent functionalisation of graphene nanoplatelets (GNs) with pyrene-conjugated Zn(II) phthalocyanines and pyrene-conjugated Zn(II) azaphthalocyanines. The GN–pyrene-conjugated Zn(II) phthalocyanine hybrid (GPc) shows a promising change from the two-photon absorption behaviour of GNs to three-photon absorption, the first such example in a graphene based hybrid system under nanosecond pulse excitation. Fluorescence and transient absorption spectroscopies are employed to describe the non-linear optical phenomena of the prepared hybrid materials. The GPc hybrid exhibits a low optical limiting threshold induced by three-photon absorption and a favourable linear transmittance (above 90%). The GN–pyrene-conjugated azaphthalocyanine hybrid (GAzaPc) also shows promising non-linear optical coefficients. A unique optical limiting performance (80% reduction in intensity) is achieved throughout the experimental range of excitation intensities. Our research offers a way to design hybrid material structures with a large effective three-photon absorption coefficient and nearly constant optical limitation across a wide intensity range with 92% linear transmittance, which would be highly useful in non-linear photonic applications.

High-power copper bromide vapor laser

A large-volume single-tube CuBr vapor laser, oscillating on the atomic copper self-terminating lines of λ510.6 nm and λ578.2 nm, is described. Characteristics of the nanosecond pulsed longitudinal discharge excitation for a maximum output power on these laser lines are found. A record-high average laser power of 140 W for atomic self-terminating CuBr vapor lasers is reported.

Chromophore Orientation-Dependent Photophysical Properties of Pyrene-Naphthalimide Compact Electron Donor-Acceptor Dyads: Electron Transfer and Intersystem Crossing.

In order to study the effect of mutual orientation of the chromophores in compact electron donor-acceptor dyads on the spin-orbit charge transfer intersystem crossing (SOCT-ISC), we prepared naphthalimide (NI)-pyrene (Py) compact electron donor-acceptor dyads, in which pyrene acts as an electron donor and NI is an electron acceptor. The connection of the two units is at the 4-C and 3-C positions of the NI unit and the 1-position of the pyrene moiety for dyads NI-Py-1 and NI-Py-2, respectively. A charge transfer absorption band was observed for both dyads in the UV-vis absorption spectra. Upon nanosecond pulsed laser excitation, long-lived triplet states (lifetime is 220 μs) were observed and the triplet state was confined to the pyrene moiety. The ISC efficiency is moderate to high in nonpolar to polar solvents (singlet oxygen quantum yield: ΦΔ = 14-52%). Ultrafast charge separation (ca. 0.81 ps) and charge recombination-induced ISC (∼3.0 ns) were observed by femtosecond transient absorption spectroscopy. Time-resolved electron paramagnetic resonance spectroscopy confirms the SOCT-ISC mechanism; interestingly, the observed electron spin polarization pattern of the triplet state is chromophore orientation-dependent; and the population rates of the triplet sublevels of NI-Py-1 (Px:Py:Pz = 0.2:0.8:0) are drastically different from those of NI-Py-2 (Px:Py:Pz = 0:0:1).

Uniform and stable plasma reactivity: Effects of nanosecond pulses and oxygen addition in atmospheric-pressure dielectric barrier discharges

Uniform and stable reactivity of atmospheric pressure plasmas is a prerequisite for most applications in fields ranging from materials’ surface processing, environment protection, to energy conversion. Dielectric barrier discharges (DBDs) are among the most promising plasmas to satisfy these requirements. However, the unpredictable and uncontrollable transitions between discharge modes, the limited understanding of the DBD ignition and extinction processes, and the complexity of plasma chemistries and reactions with admixture gases restrict their adoption in industry. Here, we report a practically relevant and elegant solution based on using customized nanosecond (ns) pulse excitation and precise addition of oxygen to an Ar flow. The effects of ns pulses and oxygen on the uniformity and reactivity of the DBD are investigated via quantifying the gap voltage Ug and the discharge current Ig from the current–voltage measurements and quantitative discharge imaging. The electron density, ne, is estimated with Ug and Ig. With increasing Ug, more electron avalanches are ignited and overlap, which facilitate ne, Te, and discharge uniformity, while high Ug induces excessive electrons generated with high ionization rates, resulting in the distortion of the space electric field and reduced stability and uniformity. A small amount of added oxygen favors the production of electrons. Overdosed oxygen molecules capture electrons causing a drop in ne and Te and couple with the effect of the electrical field resulting in the filamentary discharges or complete plasma extinction. The mechanism of the effects of ns pulses and oxygen addition on the uniformity and reactivity of plasmas is based on the electrical measurements and discharge image analysis and is cross-validated by optical emission spectra measurements and the ratio of the Ar intensities’ calculations as indicators of the variation in ne and Te. The results in this work contribute to the realization and controllability of uniform, stable, and reactive plasmas at atmospheric pressure.

Nonlinear optical behavior and optical power limiting characteristics of peripheral symmetrical and non-symmetrical zinc phthalocyanines with nanosecond pulsed excitation

In this study, the optical nonlinear absorption and optical limiting performances of symmetrical and non-symmetrical zinc phthalocyanines in tetrahydrofuran (THF) solution were conducted by the open aperture z-scanning technique. A new non-symmetrically substituted metallophthalocyanine, namely 2(3)-[(4-nitrophenyl)ethynyl]-{9(10),16(17),23(24)-tris-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zinc(II) (1b), was synthesized and then characterized by applying different spectroscopic methods, such as FT-IR, 1H NMR and MALDI-TOF spectroscopy. According to the literature, {2(3),9(10),16(17),23(24)-tetrakis-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zin(II) (1a), {2,3,9,10,16,17,23,24-octakis-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zinc(II) (2a) and 2(3)-[(4-nitrophenyl)ethynyl]-{9,10,16,17,23,24-hexakis-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zinc(II) (2b) were prepared. The effect of the symmetry and substituent’s number on the nonlinear behavior was determined. A Nd:YAG laser, nanosecond pulsed at 532 nm, was used as the excitation source. The measurements of the input-output power and the nonlinear transmission properties were carried out for different excitation power values and different concentrations of the phthalocyanines in the THF solution. The nonlinear absorption coefficient of βand the imaginary part of the third order nonlinear susceptibility of the medium (X3) were found to be strongly dependent on the concentration. All the zinc phthalocyanine complexes showed good optical limiting performances, attributed to a reverse saturable absorption (RSA) process. The results indicate that the zinc phythcyanine complexes are promising candidates for optical limiting materials.

Resonance Raman Scattering Spectra of Co(II)- and Cu-5,10,15,20-Tetrakis[4-(N-methylpyridyl)]porphyrin in the dd Excited State and Mechanisms of Its Deactivation in a Solution and in Complexes with DNA

Resonance Raman scattering (RRS) spectra of the complexes of 5,10,15,20-tetrakis[4-(N-methylpyridyl)]porphyrin with Co(II) and Cu(II) (CoIITMpyP4 and CuTMpyP4) in various solvents and in complexes with DNA are studied. Under nanosecond pulsed excitation, additional lines have been found in the RRS spectra of CoIITMpyP4 in a dimethylformamide (DMF) solution containing formic acid as an impurity and in a complex with DNA. At the same time, such lines are absent in the spectra of CoIITMpyP4 in pure DMF, dimethyl sulfoxide, water, and alcohols under the same excitation conditions. To interpret the experimental data, we have calculated the structure and vibrations of the solvate complexes of CoIITMpyP4 and CuTMpyP4 with water, methanol, and formic acid in the ground and in excited states. Based on the obtained data, additional lines in the Raman spectra are assigned to the dd excited state corresponding to the d(z2) → d(x2 – y2) transition, the lifetime of which increases with the formation of complexes of CoIITMpyP4 with formic acid. According to the calculation results, this correlates with a decrease in rate constant kic of the internal conversion due to an increase in energy gap ΔE between the ground and dd states of CoIITMpyP4. A decrease in the kic value in the case of binding of CoIITMpyP4 and CuTMpyP4 to DNA is caused by the additional interaction of the extra-ligand water molecule with one of its bases directly or via several water molecules immobilized on DNA surface. This complicates the conformational rearrangement of the water molecule in the dd excited state, which gives rise to an increase in the ΔE value.

Spontaneous and Stimulated Emission in Thin Films of Cu(In1 –xGax)(SySe1 –y)2 Solid Solutions in the Сomposition of Solar Cells

The emission spectra of thin nanocrystalline films of Cu(In1 – xGax)(SySe1 – y)2 (CIGSSe) direct-gap solid solutions in the structure of solar cells, recorded upon continuous-wave laser excitation (~0.5 W/cm2) and nanosecond pulsed laser excitation with a power density in the range of 0.1–53 kW/cm2 at temperatures ranging from 10 to 300 K, are analyzed. It is found that stimulated emission (SE) occurs in thin CIGSSe films at temperatures from 10 to 90 K in the spectral range hν = 1.062–1.081 eV, with a minimum threshold-pump level of ~1 kW/cm2. It is shown that the spontaneous emission band is blue-shifted with an increase in the excitation intensity. It is also established that, with an increase in temperature, the photoluminescence (PL) band (upon weak excitation) and the stimulated-emission band are blue-shifted, whereas the PL band is red-shifted upon strong excitation. The possible reasons and mechanisms for the influence of temperature and excitation intensity on the spectral positions of the spontaneous and stimulated emission bands for the solid-solution films are discussed.