Photoluminescence Spectra Of Structures Research Articles

IR Emission Band and Multiple-Peak Structure in Photoluminescence Spectra of SnO2:Mn

SnO2:Mn phosphor was synthesized by chemically etching metallic Sn and Mn shots in aqueous HNO3 solution. The synthesized phosphor was investigated by photoluminescence (PL), PL excitation spectroscopies, and PL decay time measurements. The PL spectra of SnO2:Mn exhibited a strong IR emission at ∼800 nm and green/red (G/R) emission. The G/R emission band was also observed in undoped SnO2. These emission bands were attributed to the Mn2+ (IR) and Sn2+ (G/R) ions in the SnO2 host, respectively. The IR emission band exhibited multiple-peak structure with an energy interval of ∼13 meV, in agreement with the Fourier transform analysis. The activation energies of the IR and G/R emission bands were determined to be ∼0.3 eV. The PL decay times were ∼2 ms and ∼2 μs for the IR and G/R emissions, respectively. The integrated PL intensity for the IR emission band showed a gradual increase with increasing temperature at T = 20–130 K. These unique tempearture dependence and multiple-peak structure were well explained by the configurational-coordinate model with the aid of the Franck–Condon principle. Resonant energy transfer from Sn2+ to Mn2+ is the cause of an appearance of the IR emission band in SnO2:Mn.

Preparation and photoluminescence of Eu‐doped GaN films by radio frequency magnetron sputtering method

AbstractThe red‐luminescent Eu‐doped GaN film has been prepared on both sapphire and GaN/sapphire substrates by the conventional RF magnetron sputtering method using a compound powder target (GaN + EuN), N2 sputtering gas and subsequent annealing in NH3. The GaN:Eu layers exhibited a red sharp photoluminescence (PL) line at 622 nm due to 5D0–7F2 transition of Eu3+ ions together with series of narrow PL lines: 5D1–7F1 (540 nm), 5D0–7F1 (580–600 nm), and 5D0–7F3 (665 nm). Dependence of Eu‐related PL on the growth condition is described: Eu‐doping level (EuN in target), substrate temperature (Ts), growth time, and annealing temperature (Ta). The optimum conditions for luminescent GaN:Eu are: (i) the Eu of 2 mol% in target, (ii) Ts at 400–450 °C, and (iii) Ta at 1000 °C for 2 hours. Improvements in intensity and reproducibility of Eu‐related PL have been attained by: (i) the increase of growth time, (ii) the use of undoped GaN buffer layer, (iii) the improvement of the target quality, and (iv) the use of the MOVPE grown GaN/Al2O3 template. Preliminary studies of various PL properties are described: the fine structure in PL spectra, PL decay characteristics, temperature dependence and photoluminescence excitation spectrum (PLE). The PL results are discussed in comparison with those in the GaN:Eu grown by other methods in literature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Free-exciton spectra in heteroepitaxial ZnSe/GaAs layers

The free-exciton photoluminescence (PL) and reflection spectra of metal-organic vapor-phase-epitaxy grown ZnSe/GaAs epilayers with a thickness greater than that of the strain relaxation thickness were studied experimentally and theoretically for temperatures in the range $T=10--120\mathrm{K}.$ Calculations were performed in the framework of absorbing and reflecting dead layer models, using single and two-oscillator models, both including and neglecting spatial dispersion. The results rule out the explanation that the fine structure in the free-exciton PL spectra derives from thermal strain splitting and polariton effects, if this structure is not accompanied by a corresponding structure in reflection. It was shown that this structure in the PL spectrum originates mainly from light interference caused by the presence of a dead layer in the near-surface region, with the thickness of the dead layer depending on the excitation intensity. A correlation between the measured and inherent free-exciton spectra was established.

Photoluminescence study on coarsening of self-assembled InAlAs quantum dots on GaAs (001)

Red-emission at similar to 640 nm from self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots grown on GaAs substrate by molecular beam epitaxy (MBE) has been demonstrated. We obtained a double-peak structure of photoluminescence (PL) spectra from quantum dots. An atomic force micrograph (AFM) image for uncapped sample also shows a bimodal distribution of dot sizes. From the temperature and excitation intensity dependence of PL spectra, we found that the double-peak structure of PL spectra from quantum dots was strongly correlated to the two predominant quantum dot families. Taking into account quantum-size effect on the peak energy, we propose that the high (low) energy peak results from a smaller (larger) dot family, and this result is identical with the statistical distribution of dot lateral size from the AFM image.

Two-band structure in photoluminescence spectra from porous silicon and its dependence on excitation wavelength

We have systematically measured the room-temperature photoluminescence spectra with a two-band structure from porous silicon (PS), as a function of excitation wavelengths in a wavelength range from 260 to 460 nm. Each spectrum can be fitted by two Gaussian functions centered at about 610 and 700 nm, the intensities of the two bands change with excitation wavelength and the intensity maxima occur when the excitation wavelength is about 340 and 400 nm, respectively. When the excitation wavelength exceeds 420 nm, the band at 610 nm is very weak. The above phenomena can be accounted for in the quantum confinement/luminescence centers model [G. G. Qin and Y. Q. Jia, Solid State Commun. 86, 559 (1993)], where it is supposed that there are two kinds of luminescence centers in SiOx layers covering the nanoscale silicon units in PS.

Variation of double-peak structure in photoluminescence spectra from porous silicon with excitation wavelength

We have systematically observed at room temperature the variations of photoluminescence(PL) from porous silicon(PS) with excitation wavelength in a range from 260 to 460nm at 20nm intervals. In the range from 260 to 320nm, the PL spectra for one of the two studied samples show clear double-peak structure. Each spectrum can be fitted by two Gaussian functions with their peaks centered at about 610nm and 710nm, respectively. The peak position and the full width at half maximum of the two Gaussian functions change little with excitation wavelength. The above phenomena seem hard to interpret using the quantum confinement model, but can be understood in the quantum confinement/luminescence centers model (G.G.Qin and Y.Q.Jia, Solid State Commun. 86, 559(1993)), if we suppose that there are two kinds of luminescence centers adsorbed on the surfaces of nane-scale silicon (NS) units or situated in the SiO x layers covering the NS units in PS.

Physical and electronic structure of amorphous silicon carbon hydrogen alloy

The physical and electronic structure of hydrogenated amorphous silicon carbide (a-SiC:H) are identified by measuring its photoluminescence and infrared spectra at various stages of thermal annealing. It is found that Brodsky’s [Solid State Commun. 36, 55 (1980)] quantum well model can be successfully applied to explain the observed results, such as the double peak structure in photoluminescence spectrum and the physical origin of the optical gap widening due to carbon incorporation.