Photoluminescence Spectral Features Research Articles

Practical consideration on Racah parameter and Tanabe−Sugano diagram analyses for Mn4+ and Cr3+-activated phosphors

The Racah parameters and Tanabe−Sugano (T−S) diagram are widely used as describing the electron−electron repulsion effects within the metal complexes in coordination chemistry. The present study discusses the Racah and related parameters for the Mn4+ and Cr3+-activated phosphors. The main subjects are two-fold: (i) to clarify how different input parameters of the excited-state energies make a difference in the Racah parameters derived from the general model and (ii) to further clarify the differences between the general and our newly proposed models. The three different excited-state energies of (1) the zero-phonon line energy, (2) the photoluminescence (PL) and/or PL excitation (PLE) peak energies, and (3) the Stokes shift-corrected PLE peak energy are considered in (ii). It is shown that the choice of such excited-state energies is of crucial importance for obtaining reliable Racah parameters and T−S diagram. The present analysis of (ii) also suggests our newly proposed model to promise the Racah parameters being satisfied the requirements of B and C to be smaller than and their ratio of C/B being not largely changed from the free-ion values. The lattice temperature effects on the PL and PLE spectral features of the 3d3 ion-activated phosphors are also discussed in detail.

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.

Investigation on the microstructural, optical and magnetic properties of Ce doped ZnO nanorods

Surfactant free wet chemical route is employed to synthesize Zn1-xCexO (x = 0.01, 0.03 and 0.05) nanorods. Effects of Ce doping on the microstructural, optical and magnetic properties of the ZnO nanorods are reported. X-ray diffraction study revealed the hexagonal wurtzite phase of ZnO with formation of secondary phase corresponding to CeO2. Nanorod nature of the samples was confirmed from field emission scanning electron microscope micrograph. The systematic decrease of band gap from 3.192 to 3.177 eV with increasing Ce doping concentration from 1 to 5% was evidenced from UV–Visible characterization. The photoluminescence spectral feature confirms the presence of intrinsic defects like zinc, oxygen vacancies etc. The different functional groups were identified from Fourier transform infrared spectra. A very weak ferromagnetic ordering was observed in all the samples at room temperature. Our study suggested that the synthesized Ce doped ZnO nanorods could be useful for optical device applications in the UV region.

Photoluminescence down-shifting studies of thermally stable Eu3+ ions doped borosilicate glasses for visible red photonic device applications

In this paper we report the synthesis of thermally stable borosilicate glasses doped with europium ions having chemical composition 35B2O3.20SiO2.(15-x)Al2O3.15ZnO.15Na2CO3.xEu2O3 (x = 0.5 to 2.5 mol%) using melt quench process. A broad hump without any sharp peaks observed in the XRD spectrum recorded for an undoped glass confirm its glassy nature. The DSC & TGA has been conducted on an undoped glass to understand thermal stability and aggregate weight loss. Raman spectrum recorded for an undoped glass reveal various functional groups present in the host glass along with its phonon energy. The absorption spectral features recorded for the as prepared glasses are used to estimate optical band gap. In the process of understanding the effective usage of the as prepared glasses in visible red photonic device applications, the spectral features such as photoluminescence (PL) excitation, PL emission and PL decay were recorded and analyzed. Under 393 nm sharp excitation, all the glass samples are showing red emission corresponds to 5D0 → 7F2 transition (612 nm) and whose intensity continuously increasing with Eu3+ ion concentration up to 2.5 mol%. The red to orange color ratio (R/O) estimated from the recorded PL spectral features varies from 3.62 to 3.92 within the variation limits of Eu3+ions from 0.5 to 2.5 mol% indicates relatively low symmetry around Eu3+ ions in the as prepared glasses. Relatively higher R/O ratio also reveals that the nature of bonding between Eu3+ ions and the surrounding ligands as covalent. The Judd-Ofelt theory has been applied to the emission spectral features to understand the nature of bonding between the doped RE ion and its surrounding ligands along with the radiative properties of the doped RE ion. Activation energy (0.175 eV) and percentage loss (82%) in PL intensity estimated for 2.5 mol% of Eu3+ions through temperature dependent PL (TDPL) studies reveal the superiority in thermal stability of the as prepared glasses. The PL, TDPL, PL decay studies conducted along with CIE coordinates estimated allows us to contemplate that, the as prepared glasses are quite useful in fabricating thermally stable visible red photonic devices.

Effective energy transfer from Dy3+ to Tb3+ ions in thermally stable KZABS glasses for intense green emitting device applications

Potassium Zinc Alumino Borosilicate (KZABS) glasses co-doped with Dy3+/Tb3+ ions have been synthesized by employing a sudden melt quenching technique. To check the luminescence behavior, the as prepared glasses were characterized by employing spectroscopic tools like photoluminescence (PL) excitation and emission, temperature dependent PL and PL decay to see the energy transfer between Dy3+ and Tb3+ ions and optimum green emission suitable for photonic applications. The XRD spectra reveals the amorphous nature of the as prepared KZABS glasses. PL spectral features show optimum green emission and confirms energy transfer from Dy3+ to Tb3+ ions. With the help of temperature dependent PL, glasses were found to be thermally stable. The decay profiles recorded show bi-exponential nature and demonstrates the energy transfer that took place from Dy3+ to Tb3+ ions. The Inokuti- Hirayama (I–H) model confirms the interaction involved in energy transfer process as dipole-dipole in nature. The CIE coordinates are found to be shifting gradually towards intense green region with increase in activator concentration (Tb3+) under the optimized sensitizer (Dy3+) concentration. It is also observed that, the CIE coordinates shifting towards intense green region when the as prepared KZABS glasses are excited with suitable excitation wavelengths of both sensitizer and activator. All the studies finally reveal the superiority of Dy3+/Tb3+ co-doped KZABS glasses for their usage in green emitting photonic device applications such as w-LEDs and display devices.

White light emission from Sm-doped YAG ceramic controlled by the excitation wavelengths

This work reports, for first time, on optically-driven white light emission from samarium-doped yttrium aluminum garnet ceramic, Sm-doped YAG. Nanocrystalline Sm-doped YAG sample has been prepared via co-precipitation method then transformed to bulk ceramic by sintering process using Spark Plasma Sintering (SPS) technique. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) are used to characterize the crystal structure of the nanocrystals. The micro-grains of the obtained ceramic have been demonstrated by scanning electron microscope (SEM). Photoluminescence (PL) and cathodoluminescence (CL) spectroscopies have been performed on the ceramic sample. It is found that the PL spectral features are strongly dependent on the excitation wavelength. Remarkable PL spectral overlapping between bluish-green band and reddish-orange lines related to host defects/impurities and Sm ions, respectively, has been obtained. In addition, controlling the relative PL spectral contributions from the host-related emission and Sm ions has been achieved by changing the excitation wavelengths. This led to manipulate the emission color coordinates as investigated by chromaticity diagram. Moreover, under certain excitation wavelengths, an intense white emission is observed with a naked eye. The origin of the white emission has been discussed in light of specific PL spectral overlapping from the host and Sm ion contributions. This work emphasizes on the role played by the host defects/impurities in the optical properties of ceramic materials that can be exploited in several lighting applications.

Spectral characterization of Dy3+ ions doped phosphate glasses for yellow laser applications

Dy3+ ions doped phosphate glasses were prepared using sudden melt quench method. The studies like XRD, FT-IR, optical absorption, photoluminescence excitation, photoluminescence (PL), and PL decay were conducted to understand the spectroscopic properties. The Judd-Ofelt (J-O) parameters evaluated from absorption spectral features were employed to evaluate various radiative parameters of Dy3+ ions in phosphate glasses. Two intense bands were observed in PL spectra, in blue and yellow regions under 387 nm excitation. The emission spectra indicate concentration quenching for phosphate glass with 1 mol% of Dy3+ ions, which may be ascribed to dipole-dipole interactions between Dy3+ ions (Dexter theory). These PL spectral features were also used to estimate Y/B intensity ratio, CIE-chromaticity coordinates to understand the utility of prepared glasses in Lasers. The stimulated emission cross-sections, branching ratios, quantum efficiencies and CIE-color coordinates evaluated to validate the suitability of the prepared glasses for yellow laser applications.

Delocalized Surface Electronic States on Polar Facets of Semiconductor Nanocrystals.

Wurtzite CdSe@CdS dot@platelet nanocrystals with (001) and (00-1) polar facets as the basal planes and (100) family of nonpolar facets as the side planes are applied for studying surface defects on semiconductor nanocrystals. When they are terminated with cadmium ions coordinated with carboxylate ligands, a single set of absorption features and band-edge photoluminescence (PL) with near unity PL quantum yield and monoexponential PL decay dynamics (lifetime ∼28 ns) are observed. In addition to these spectral signatures, when the surface is converted to sulfur-terminated, a second set of sharp absorption features with decent extinction coefficients and a secondary band-edge PL with low PL quantum yield and long-lifetime (>78 ns) PL decay dynamics are reproducibly recorded. Photochemical analysis confirms that the secondary UV-vis and PL spectral features are quantitatively correlated with each other. Chemical analysis and X-ray photoelectron spectroscopy measurements confirm that such secondary spectral features are well correlated with the sulfide (such as -SH) and disulfide (such as -S-S-) surface sites of a basal plane, which likely form surface hole electronic states delocalized on the entire basal plane. Results suggest that, for studying surface defects on semiconductor nanocrystals, it is essential to prepare a nearly monodisperse surface structure in terms of facets and surface chemical bonding.

Review—Mn4+-Activated Red and Deep Red-Emitting Phosphors

Mn4+-activated phosphors are a new class of non-rare earth phosphors and are alternative to commercial Eu2+-activated nitride/oxynitride phosphors with growing interest in various applications. In this review article, the structural and photoluminescence (PL) properties of various Mn4+-activated phosphors have been discussed. The host materials considered here can be roughly classified into five groups; fluorides, oxides, oxyfluorides, and two fluorine compounds. Phosphors of each group can also be classified into totally eleven subgroups from their different PL spectral features, e.g., whether an appearance of the zero-phonon line (ZPL) emission peak or not. The ZPL emission and absorption energies of the Mn4+ ions have been determined from the PL and PL excitation spectra using the Franck−Condon analysis method within the configurational-coordinate (CC) model. These results are used to obtain reliable phosphor parameters, i.e., the crystal-field (Dq) and Racah parameters (B and C), of the Mn4+ ions in the various host materials. The PL intensity vs temperature data, together with those of the luminescence lifetimes, are modeled on the basis of the CC model, and an excellent agreement has been achieved if not only the optical phonon but also the acoustic phonon contribution is taken into consideration in the conventional thermal quenching model. Effects of the hydrostatic pressure and dopant concentration on the PL spectral features are also discussed. Finally, key properties of the Mn4+-activated phosphors are discussed for use of such red and deep red-emitting phosphor systems in warm w-LED and indoor plant cultivation applications.

Dazzling red luminescence from Bi3+/Eu3+: CaLa2ZnO5 nanophosphor spheres for high luminescence quantum yield

We have successfully synthesized co-doped Bi3+/Eu3+: CLZO nanophosphor spheres by citrate sol-gel method. Tetragonal structure has been confirmed from the XRD analysis. Morphological studies were carried out from FE-SEM analysis for the optimized sample. EDAX and XPS measurements were employed to confirm the presence of elements and their ionic states. The homogeneous shape, size and crystalline planes of the phosphor crystalline nanosphere have been clearly demonstrated by HR-TEM analysis. Photoluminescence (PL) spectral profiles reveal that the strong red emission has been noticed at 626 nm (5D0→7F2) from the Eu3+: CLZO phosphors under the visible excitation of 467 nm. The PL performance has been remarkably enhanced by increasing the Eu3+ ion concentration. By co-doping with Bi3+ ions to Eu3+: CLZO phosphors, the red emission pertaining to Eu3+ was appreciably enhanced through energy transfer from Bi3+ to Eu3+ ions. The energy transfer mechanism from Bi3+ to Eu3+ ions has been demonstrated by partial energy level scheme diagram. Commission International de I'Echairage (CIE) 1931 chromaticity coordinates (x-y) calculated for singly Eu3+(12 mol %): CLZO and co-doped Eu3+(12 mol %)+Bi3+(1 mol %): CLZO nanophosphor spheres and they were found to be (0.6644, 0.3355) and (0.6688, 0.3311) respectively. The Correlated Color Temperature (CCT) value was evaluated as 3059 K for co-doped sample. Moreover, lifetime and quantum efficiency for Eu3+ emission were significantly enhanced upon co-doping with Bi3+ ions to the Eu3+ doped CLZO nanophosphor spheres. The energy transfer phenomenon from Bi3+ to Eu3+ ions was clearly elucidated by several fluorescence dynamics such as overlapped spectral studies, photoluminescence spectral features, CIE color coordinates and quantum efficiency. These dazzling red luminescent nanophosphor spheres material could be suggested as a promising candidate for solid state illumination and optical display devices.

Relationships between textural and photoluminescence spectral features of carbonado (natural polycrystalline diamond) and implications for its origin

Field Emission SEM (FESEM) textural observations, crystal size distribution (CSD) analyses, UV-excited luminescence imaging, and photoluminescence (PL) microspectroscopy excited by 488 nm laser were conducted on two texturally contrasting samples of carbonado, a kind of natural polycrystalline diamond from the Central African Republic (CAR). The investigated carbonado samples A and B show extremely different textures: sample A is made up of faceted crystals accompanied by abundant, small rectangular pores, whereas sample B has a granular texture with coarser crystals and scarce, large pores. Diamond crystals smaller than 2–3 µm are enriched in sample A but depleted in sample B. These textural features indicate that sample B diamonds were annealed under thermodynamically stable P–T conditions. The pore characteristics indicate that fluid permeability was higher for sample A than sample B. Photoluminescence (PL) spectra indicate that samples A and B correspond to Group A and B carbonados in the classification of Kagi et al. (1994), respectively, so that sample A reveals emissions from the H3 center without any N–V0 derived emission at 575 nm, whereas sample B shows emissions from the 3H center and the N–V0 defect. In addition, UV-excited luminescence images and photoluminescence spectra for sample B indicate that the rims of diamond crystals within several microns of a pore show luminescence features similar to those of Group AB carbonados (Kagi et al., 1994), indicating that this Group AB material was formed from Group B by irradiation from pore-filling, radioactive-element-bearing materials at a low temperature. The extent of the low-temperature irradiation is considered to depend on fluid permeability, and the Group A material was strongly irradiated due to its permeable texture whereas the Group B material was not significantly irradiated due to its less permeable granular texture. These results indicate that Group B carbonados have retained their original PL spectral features produced under high pressures and temperatures at mantle depths.

Structural change induced by thermal annealing of red-light-emitting ZnSnF6 ∙ 6H2O:Mn4+ hexahydrate phosphor

Effects of thermal annealing on the red-emitting ZnSnF6 ∙ 6H2O:Mn4+ hexahydrate phosphor properties were investigated using X-ray diffraction measurement (XRD), photoluminescence (PL) analysis, and Raman scattering spectroscopy. Thermal annealing was performed at Ta = 50 to 400 °C in air for 1 h. Mn4+-related red emission wavelengths were redshifted about 5 nm after annealing at Ta ≥ 200 °C with greatly decreased emission intensities. This change in PL spectral feature was attributed to the dehydration of the hexahydrate phosphor, supported by the XRD and Raman scattering results. The XRD and PL intensity analyses determined thermal decomposition energies of ∼0.3 eV from the ZnSnF6 ∙ 6H2O hexahydrate to anhydrate and of ∼0.9 eV from the ZnSnF6 anhydrate to metallic fluorid/oxide (ZnF2/SnO2). A comparative discussion was given on the PL properties of two different Mn4+-activated phosphors, Ba–IV–F6:Mn4+ anhydrate and Zn–IV–F6 ∙ 6H2O:Mn4+ hexahydrate phosphors with IV = Si, Ge, and Sn.

Effect of Ag/Au bilayer assisted etching on the strongly enhanced photoluminescence and visible light photocatalysis by Si nanowire arrays.

We report on the strongly enhanced photoluminescence (PL) and visible light photocatalysis by arrays of vertically aligned single crystalline Si nanowires (NWs) grown by Ag/Au bilayer assisted etching. High resolution FESEM and TEM imaging reveals that the Si NWs are decorated with ultra-small size arbitrary shaped Si nanocrystals (NCs) due to the lateral etching of the NWs. A strong broad band and tunable visible to near-infrared (NIR) photoluminescence (PL) in the range 1.3-2.4 eV are observed for these Si NWs/NCs at room temperature, depending on the etching conditions. Our studies reveal that the visible-NIR PL intensity is about two orders of magnitude higher and it exhibits faster decay dynamics in the bilayer assisted etching case as compared to the Ag or Au single layer etching case. The enhanced PL in the bimetal case is attributed to the longer length and higher density of the Si NWs/NCs, surface plasmon resonance enhanced absorption by residual bimetal NPs and the enhanced radiative recombination rate. Studies on the time evolution of PL spectral features with laser exposure under ambient conditions and laser power dependence reveal that both the quantum confinement of carriers in Si NCs and the nonbridging oxygen hole defects in the SiOx layer contribute to the tunable PL. Interestingly, Si NWs grown by Ag/Au bilayer assisted etching exhibit enhanced photocatalytic degradation of methylene blue in comparison to Si NWs grown by single layer Ag or Au assisted etching. The Schottky barrier present between bimetallic NPs and nanoporous Si NWs with Si-H bonds facilitates the photocatalytic activity by efficient separation of photogenerated e-h pairs. Our results demonstrate the superiority of the Si NW array grown by bilayer assisted etching for their cutting edge applications in optoelectronics and environmental cleaning.

Phonon induced luminescence decay in monolayer MoS2 on SiO2/Si substrates

Exfoliated monolayer MoS2 films on SiO2/Si substrates have been studied using photoluminescence (PL), Raman and reflectance contrast (RC) spectroscopies. With increase in temperature, the intensity of the two dominant PL spectral features A and D, attributed to A exciton/trion and to defects, seemingly decay in an activated fashion with an energy ∼50 meV, which is close to the energies of E2g1 and A1g phonons. Comparison of absorption spectrum derived from RC with circular polarization resolved PL spectrum suggests that both D and A emissions are associated with bound excitons, the A emission involving relatively weakly localized ones. The PL decay behaviour is explained using a phenomenological model where non-radiative loss of excitons is determined by the number of excited phonon modes. This corroborates the recent finding of strong A exciton and A1g phonon coupling in monolayer MoS2.

Effect of rapid thermal annealing on InP1−xBix grown by molecular beam epitaxy

The effect of post-growth rapid thermal annealing on structural and optical properties of InP1−xBix thin films was investigated. InPBi shows good thermal stability up to 500 °C and a modest improvement in photoluminescence (PL) intensity with an unchanged PL spectral feature. Bismuth outdiffusion from InPBi and strain relaxation are observed at about 600 °C. The InPBi sample annealed at 800 °C shows an unexpected PL spectrum with different energy transitions.

Structural dependences of localization and recombination of photogenerated carriers in the top GaInP Subcells of GaInP/GaAs double-junction tandem solar cells.

In high-efficiency GaInP/GaAs double-junction tandem solar cells, GaInP layers play a central role in determining the performance of the solar cells. Therefore, gaining a deeper understanding of the optoelectronic processes in GaInP layers is crucial for improving the energy conversion efficiency of GaInP-based photovoltaic devices. In this work, we firmly show strong dependences of localization and recombination of photogenerated carriers in the top GaInP subcells in the GaInP/GaAs double-junction tandem solar cells on the substrate misorientation angle with excitation intensity- and temperature-dependent photoluminescence (PL). The entire solar cell structures including GaInP layers were grown with metalorganic chemical vapor deposition on GaAs substrates with misorientation angles of 2° (denoted as Sample 2°) and 7° (Sample 7°) off (100) toward (111)B. The PL spectral features of the two top GaInP subcells, as well as their excitation-power and temperature dependences exhibit remarkable variation on the misorientation angle. In Sample 2°, the dominant localization mechanism and luminescence channels are due to the energy potential minima caused by highly ordered atomic domains; In Sample 7°, the main localization and radiative recombination of photogenerated carriers occur in the atomically disordered regions. Our results reveal a more precise picture on the localization and recombination mechanisms of photogenerated carriers in the top GaInP subcells, which could be the crucial factors in controlling the optoelectronic efficiency of the GaInP-based multijunction photovoltaic devices.

Optical Properties of Graphene Nanoribbons Encapsulated in Single-Walled Carbon Nanotubes

We report the photoluminescence (PL) from graphene nanoribbons (GNRs) encapsulated in single-walled carbon nanotubes (SWCNTs). New PL spectral features originating from GNRs have been detected in the visible spectral range. PL peaks from GNRs have resonant character, and their positions depend on the ribbon geometrical structure in accordance with the theoretical predictions. GNRs were synthesized using confined polymerization and fusion of coronene molecules. GNR@SWCNTs material demonstrates a bright photoluminescence both in infrared (IR) and visible regions. The photoluminescence excitation mapping in the near-IR spectral range has revealed the geometry-dependent shifts of the SWCNT peaks (up to 11 meV in excitation and emission) after the process of polymerization of coronene molecules inside the nanotubes. This behavior has been attributed to the strain of SWCNTs induced by insertion of the coronene molecules.

Effect of layer separation, InAs thickness, and rapid thermal annealing on the optical emission from a multi-layer quantum wire structure

Multi-layer InAs quantum wire stacks with different layer separations (8, 15, and 25 nm) and InAs thicknesses (3, 4, 5, and 7 monolayers [ML]) were grown on and embedded in In0.53Ga0.27Al0.20As barrier/spacer layers lattice-matched to an InP substrate. For the samples with 4 ML of InAs and different layer separations, double peak photoluminescence was observed from quantum wire stacks separated by 8 nm, and with a 15 nm spacer layer a long wavelength component was observed extending from the main peak. Only a single peak was found as the spacer layer thickness was increased to 25 nm. For the quantum wire stacks with different InAs layer thicknesses and a separation of 8 nm, double peak photoluminescence spectra were observed in the sample with 4 ML of InAs, and a main peak with a long wavelength component was obtained from the sample with 3 ML of InAs. Only a single peak was detectable for the InAs layer thicknesses of 5 and 7 ML. The optical emission features were studied via temperature and excitation laser power dependent photoluminescence. Based on the photoluminescence and transmission electron microscopy observations, photoluminescence spectral features can be attributed to a bi-modal height distribution in certain samples. In order to extend the optical emission to room temperature, the sample with 5 ML of InAs and an 8 nm spacer layer was subjected to post-growth rapid thermal annealing at different temperatures. The emission wavelength was tunable from 1.63 to 1.72 μm at room temperature.

Structural, Dielectric, Thermal and Optical Properties of Ti3+or Cr3+: PVA Polymer Films

Highly transparent and very clear natured PVA: Cr3+ and PVA: Ti3+ polymer films of good quality have been synthesized by employing solution cast method. XRD profiles of reference PVA film has shown totally amorphous nature, however due to the presence of Cr3+ or Ti3+, PVA films have acquired some crystalline natured based on the XRD profiles of these two films in comparison with the reference host film. By employing the tools of SEM and EDAX, analysis of these doped films have been made confirming the presence of dopant ions in the PVA film matrices. FTIR profiles of PVA film has been investigated for the structural details of it. For the both the transition metal ions doped PVA films, dielectric properties related profiles have been measured to understand their potentialities. In order to understand thermal properties of these films, their TG-DTA measurement have been carried out. Both optical absorption and emission spectra of these polymers have been carried out, electronic assignments to those bands have successfully been made. It is interesting to mention that a bright blue colour has been observed from the PVA: Cr3+ upon its exposure to an UV source and also PVA: Ti3+ has revealed a prominent indigo emission under an UV source. These observations have been correlated to the measured photoluminescence spectral features.

Phase evolution and photoluminescence in as-deposited amorphous silicon nitride films

A systematic study of hydrogenated amorphous silicon nitride films deposited by varying gas flow rate ratio ( R = SiH 4 /NH 3 ) using Photo-Chemical Vapour Deposition reveal that as R is increased, dominant phase changes from silicon oxynitride to silicon nitride with embedded silicon nanoclusters. The change in photoluminescence spectral features in these films is attributed to quantum confinement effect. The results suggest that hydrogen plays a crucial role in overall phase evolution and in-situ formation of Si nanoclusters embedded in silicon nitride matrix.