Photoluminescence Excitation Peak Research Articles

Synthesis and luminescence properties of Ca2AlNbO6:Fe3+ phosphor for plant growth lighting

With the development of plant growth lighting, more and more attention has been paid to red and far red luminescent materials. In this work, we synthesize successfully a non-rare earth and non-toxic Ca2AlNbO6:Fe3+ phosphor in air and investigate the crystal structure, morphology, and luminescence properties of Ca2AlNbO6:Fe3+ by using powder X-Ray Diffraction, the field emission scanning electron microscopy, and the Edinburgh steady-state FS5 spectrometer, respectively. The far-red emission with peak at 714 nm of Ca2AlNbO6:Fe3+ is due to the 4T1(4G) → 6A1(6S) transition of Fe3+ ion. Photoluminescence excitation (PLE) spectrum of Ca2AlNbO6:Fe3+ includes four PLE peaks, which are assigned to the O2− → Fe3+ charge transfer band (CTB) (309 nm), the 6A1(6S) → 4T1(4P) (364 nm), 6A1(6S) → 4E(4D) (395 nm), and 6A1(6S) → 4T2(4G) (532 nm) transitions of Fe3+, respectively. We further study the concentration/temperature dependent emission spectra and time-resolved emission spectra. The optimal Fe3+ doping concentration (0.6mol%) and the only luminous center (Fe3+) in Ca2AlNbO6:Fe3+ are confirmed. The decay curves of Ca2AlNbO6:xFe3+ (0.2 mol% ≤ x ≤ 1.2 mol%) are measured and their lifetimes decrease from 463.24 to 385.29 μs＀ The emission spectra under different temperatures prove that Ca2AlNbO6:Fe3+ has a good heat stability. We explain the luminous mechanism and concentration/thermal quenching mechanisms, and further research the application prospect of Ca2AlNbO6:Fe3+ in plant growth lighting.

Investigation on luminescent characteristics of Tb3+/Dy3+co-doped boro-phosphate glass for cool white LED and radiation shielding applications

The Tb3+/Dy3+ co-doped Boro-Phosphate Glass (BPANZDyTb) was produced (40 B2O3 + 39P2O5 + 5 Al2O3 + 5 NaF + 10 ZnO + 0.5 Tb2O3 + 0.5 Dy2O3) using melt-quenching technique. X-ray diffraction measurements, Raman, and Fourier Transform Infrared were used to evaluate the structural behavior of the prepared glass. Powder-XRD spectra, in the 10–90° range showed that the prepared glass was amorphous. FTIR analysis reveals that the network contains a variety of structural groups, including B-O-B, BO4, BO, P-O, PO2, P-O-B, and PO4 units. The UV–visible diffuse reflectance spectroscopy was used to record and study the optical linear properties of Tb3+/Dy3+ co-doped Boro-Phosphate Glass (BPANZDyTb). The photoluminescence excitation peak was obtained at 348 nm. The emission peaks were located at 484 nm (4F9/2 → 6H15/2 → blue), 576 nm (4F9/2 → 6H13/2 → yellow), and 662 nm (4F9/2 → 6H11/2 → red). Tb3+ ions are located at 412 nm (5D3 → 7F5), 441 nm (5D3 → 7F4), 546 nm (5D4 → 7F5), and 625 nm (5D4 → 7F3). The result of CIE 1931 chromaticity coordinates indicate that the prepared glass is suitable material for cold white light emitting diode applications due to its color coordinates x = 0.3106 and y = 0.3240 and correlated color temperature (CCT) values about 6768 K. The gamma-ray parameters such as half-value layer (HVL), mass attenuation coefficient (μ/ρ), mean free path (MFP), and effective atomic number (Zeff) of the BPANZDyTb glass were studied using Phy-X software. The results of the gamma-ray parameter show that the Dy3+ ions and Tb3+ ions co-doped BoroPhosphate glass is an appropriate material for radiation shielding applications.

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.

Dosimetric properties of MgAl2O4 transparent ceramics doped with Ce

Ce-doped MgAl2O4 transparent ceramics were fabricated by the spark plasma sintering method. The 0.01% Ce-doped MgAl2O4 exhibited photoluminescence (PL) peaking at 410 nm upon the excitation of 310 nm. On the other hand, the 0.1%, 0.5%, and 1% Ce-doped MgAl2O4 showed different PL excitation peaks. The PL peak at 410 nm was attributed to 5d-4f transitions of Ce3+ ions with a decay time of a few nanoseconds. Thermally stimulated luminescence (TSL) glow curves were mainly composed of three glow peaks. When Ce-doped MgAl2O4 was heated at 300 °C, three TSL emission peaks were observed at around 410, 520 and 700 nm in TSL spectra, originating from Ce3+ ions, Mn2+ impurities, and Mg2+ vacancies, respectively. The normalized TSL intensity declined to 95% for the first 24 h and did not change in 1–5 d within the measurement error. The minimum detectable dose of the 0.5% Ce-doped MgAl2O4 was 0.5 μGy.

Enhanced photoluminescence quantum yield of Ce3+‐doped aluminum–silicate glasses for scintillation application

AbstractCe3+‐doped 20Gd2O3–20Al2O3–60SiO2 (GAS:xCe3+) glasses (x = 0.3, 0.7, 1.1, 1.5, 1.9 mol%) with Si3N4 as a reducing agent were prepared. The density of the glasses is around 4.2 g/cm3. With the increase in the Ce3+ concentration, both the photoluminescence (PL) and PL excitation peaks of GAS:xCe3+ glasses show a redshift because the 4f–5d energy levels of Ce3+ ions are narrowed. PL quantum yield and PL decay time of GAS:xCe3+ glasses are 28.32–50.59% and 43–64 ns, respectively. In addition, they both first increases and then decreases with the Ce3+ concentration increasing, reached the maximum when x = 1.1 mol%. The integrated X‐ray excited luminescence (XEL) intensity of the GAS:1.1Ce3+ glass is 23.86% of that of Bi4Ge3O12 (BGO) crystal, and the light yield reaches 1200 ph/MeV with an energy resolution of 22.98% at 662 keV when exposed to γ‐rays. The PL and XEL thermal activation energies of GAS:xCe3+ glasses are independent of Ce3+ ions concentration. Scintillating decay time of the glasses exhibits two components consisting of nanosecond and microsecond levels, and the scintillating decay time gradually decreases with the Ce3+ concentration increasing. The difference between PL and scintillating decay time is discussed regarding the different luminescent mechanisms.

The Emission Mechanism of Gold Nanoclusters Capped with 11-Mercaptoundecanoic Acid, and the Detection of Methanol in Adulterated Wine Model.

The absorption and emission mechanisms of gold nanoclusters (AuNCs) have yet to be understood. In this article, 11-Mercaptoundecanoic acid (MUA) capped AuNCs (AuNC@MUA) were synthesized using the chemical etching method. Compared with MUA, AuNC@MUA had three obvious absorption peaks at 280 nm, 360 nm, and 390 nm; its photoluminescence excitation (PLE) peak and photoluminescence (PL) peak were located at 285 nm and 600 nm, respectively. The AuNC@MUA was hardly emissive when 360 nm and 390 nm were chosen as excitation wavelengths. The extremely large stokes-shift (>300 nm), and the mismatch between the excitation peaks and absorption peaks of AuNC@MUA, make it a particularly suitable model for studying the emission mechanism. When the ligands were partially removed by a small amount of sodium hypochlorite (NaClO) solution, the absorption peak showed a remarkable rise at 288 nm and declines at 360 nm and 390 nm. These experimental results illustrated that the absorption peak at 288 nm was mainly from metal-to-metal charge transfer (MMCT), while the absorption peaks at 360 nm and 390 nm were mainly from ligand-to-metal charge transfer (LMCT). The PLE peak coincided with the former absorption peak, which implied that the emission of the AuNC@MUA was originally from MMCT. It was also interesting that the emission mechanism could be switched to LMCT from MMCT by decreasing the size of the nanoclusters using 16-mercaptohexadecanoic acid (MHA), which possesses a stronger etching ability. Moreover, due to the different PL intensities of AuNC@MUA in methanol, ethanol, and water, it has been successfully applied in detecting methanol in adulterated wine models (methanol-ethanol-water mixtures).

Enhancement of blue emission in Ce3+, Eu2+ activated BaSiF6 downconversion phosphor by energy transfer mechanism: A photochromic phosphor

Rare earth activated fluoride phosphors have attention in recent years in the field of solid state lighting. In the present study, RE (RE = Ce3+,Eu2+) doped/co-doped BaSiF6 phosphor has been synthesized by low temperature solution combustion method at 500 ± 20 °C using urea as a fuel. Photoluminescence (PL) properties of this sample were investigated by RF-5301 PC Spectrofluorophotometer. The structural, vibrational features and morphology of all the samples were analyzed by X-ray Diffraction (XRD), and Fourier Transform-Infrared Spectroscopy (FT- IR) which showed that the samples were crystallized in a well known structure. Photoluminescence characterization of Eu2+ doped phosphor shows a blue emission at λmax ~460 nm under the excitation of 287 nm. The photoluminescence properties of the as‐prepared phosphors were investigated and the Ce3+ ions in these hosts were found to give little broadband emission in the UV range at 344 nm on exciting it at 300 nm. A broad PL excitation peak is obtained on co-doping Ce3+ with Eu2+ in the range of 300–425 nm highest intensity at 362 nm gives broad blue emission at 440 nm. This luminescent powder are expected to find out potential applications in the blue emitting phosphor converted white light emitting diodes and optical display systems.

Synthesis and photoluminescence properties of Eu3+ -activated Ba2 Mg(PO4 )2 phosphor.

In this paper, we have reported the photoluminescence (PL) properties of the Ba2 Mg(PO4 )2 :Eu3+ phosphor synthesized using a wet chemical method. The preliminary scanning electron microscopy (SEM) investigation of the sample revealed irregular surface morphology with particle sizes in the 10-50 μm range. The strongest PL excitation peak was observed at 396 nm. The emission spectra indicated that this phosphor can be effectively excited by the 396 nm wavelength. Upon 396 nm excitation, the emission spectrum showed characteristics peaks located at 592 nm and 615 nm. These intense orange-red emission peaks were obtained due to f→f transitions of Eu3+ ions. The emission peak at 592 nm is referred to as the magnetic dipole 5 D0 →7 F1 transition and the emission peak at 615 nm corresponded to the electric dipole 5 D0 →7 F2 transition of Eu3+ . The Commission Internationale de l'Eclairage (CIE) coordinates of the Ba2 Mg(PO4 )2 :Eu3+ phosphor were found to be (0.586, 0.412) for wavelength 592 nm and (0.680, 0.319) for wavelength 615 nm situated at the edge of the CIE diagram, indicating high colour purity of phosphors. Due to the high emission intensity and a good excitation profile, Eu3+ -doped Ba2 Mg(PO4 )2 phosphor may be a promising orange-red phosphor candidate for solid-state lighting applications.

Twisted bilayer graphene photoluminescence emission peaks at van Hove singularities

We report on photoluminescence emission imaging by femtosecond laser excitation on twisted bilayer graphene samples. The emission images are obtained by tuning the excitation laser energies in the near infrared region. We demonstrate an increase of the photoluminescence emission at excitation energies that depends on the bilayer twist angle. The results show a peak for the light emission when the excitation is in resonance with transitions at the van Hove singularities in the electronic density of states. We measured the photoluminescence excitation peak position and width for samples with various twist angles showing resonances in the energy range of 1.2 to 1.7 eV.

Photoluminescence properties of white light emitting La2O3:Dy3+ nanocrystals

White light emitting nanocrystalline La2O3:Dy3+ phosphors with different concentration (0.5–2 at.%) were synthesized by simple precipitation method. X-ray diffraction (XRD) pattern indicates all the samples crystallizes in the hexagonal phase. Average crystallite sizes of the samples calculated from XRD data were found to be in the range of 20–55 nm. Transmission electron microscopy, selected area electron diffraction, energy dispersive analysis of X-ray and photoluminescence (PL) of the samples are also reported. Strong PL excitation peak due to charge transfer band was observed at 230 nm. Photoluminescence emission peaks observed at 486 and 575 nm were probably attributed to 4F9/2–6H15/2 and 4F9/2–6H13/2 of Dy3+ ions respectively. Optimum luminescence intensity is found at 1 at.% Dy3+ doped La2O3 sample. Further, Commission Internationale de l'e clairage (CIE, 1931) co-ordinates and correlated color temperature (CCT) of the doped sample were calculated to investigate the phosphors’ performance and technical applicability of the emitted light respectively. CCT of the 0.5 and 1 at.% samples is 5894 K (white light), within the range of vertical daylight, which makes the synthesised samples promising nanophosphor and may find application in simulating vertical daylight of the Sun.

Tellurium quantum dots: Preparation and optical properties

Herein, we report an effective and simple method for producing Tellurium Quantum dots (TeQDs), zero-dimensional nanomaterials with great prospects for biomedical applications. Their preparation is based on the ultrasonic exfoliation of Te powder dispersed in 1-methyl-2-pyrrolidone. Sonication causes the van der Waals forces between the structural hexagons of Te to break so that the relatively coarse powder breaks down into nanoscale particles. The TeQDs have an average size of about 4 nm. UV-Vis absorption spectra of the TeQDs showed an absorption peak at 288 nm. Photoluminescence excitation (PLE) and photoluminescence (PL) are used to study the optical properties of TeQDs. Both the PLE and PL peaks revealed a linear relationship against the emission and excitation energies, respectively. TeQDs have important potential applications in biological imaging and catalysis as well as optoelectronics.

Photoluminescence and thermoluminescence properties of BaGa2O4

Rare–Earth free luminescent materials are fast becoming important as the cost of rare earth ions gradually increases. In this work, a Rare–Earth free BaGa2O4 luminescent compound was prepared by solid state chemical reaction, which was confirmed to have a single phase by X-ray Diffraction. The Backscattered Electron image and Energy Dispersive X-ray spectroscopy maps confirmed irregular particle and homogeneous compound formation, respectively. The Photoluminescence spectrum displayed broad emission between 350 to 650nm, which was deconvoluted into two components. The photoluminescence excitation peak was positioned at 254nm, which corresponds with the band-to-band position observed from the diffuse reflectance spectrum. The band gap was extrapolated to 4.65 ± 0.02eV using the Kubelka-Munk model. The preliminary thermoluminescence results indicated that the kinetics involved were neither of first nor second order. Additionally, the activation energy of the electrons within the trap centres was approximated to 0.61 ± 0.01eV using the Initial Rise model.

Optimization of InAs quantum dots through growth interruption on InAs/GaAs quantum dot heterostructure

This study investigates the optical and structural properties of multilayer InAs QDs heterostructures designed with varying levels of growth interruption. Samples were subject to growth interruptions of 0, 25, 50, and 75s (samples A, B, C, and D, respectively). Low-temperature (9K) photoluminescence (PL) experiments revealed an initial redshift in the ground-state emission peak (from 1131 to 1145nm) as growth interruption (GI) was varied from 0 to 25s. In addition, we observed a blueshift (from 1145 to 1100nm) when the interruption lasted for more than 25s. The thermal activation energies of samples A–D, calculated from temperature-dependent (8–300K) PL experiments, were approximately 182.4, 241.5, 206.2 and 175.3meV, respectively. The photoluminescence excitation (PLE) studies reveal the existence of two strong peaks at each detection energy, one at ~ 63meV and other at ~ 140meV. These two PLE peaks arise from the InAs QDs shifting toward the higher energy (meV) levels which have lower intensities with the increase of GI. Longer GI time increases the intensities of InAs wetting layer as well as GaAs matrix. This, in turn, worsens the optical property. In our structural study, high-resolution transmission electron microscopy (HRTEM) confirmed that a short interruption (25s, Sample B) in the growth of QDs produced a better size homogeineity. We also observed that Sample B has a tensile stress along the growth direction (001), which increased the height of the InAs QDs to approximately 8nm with the interplanar distance of 0.626Å along the 001 planes. In addition, the InAs QDs maintained their geometrical shape till 50s and the shape of the dots started deterioting after 50s as a result of the decrease in QDs height of 2nm revealed from HRTEM. In contrast, high-resolution X-ray diffraction (HRXRD) found the strain energy drastically dropped to 0.4765meV/atoms (75s, Sample D) from 0.819meV/atoms (25s, Sample B), showing inhomegenous QDs size distribution. Higher strain energy of 0.819meV in the stacked heterostructure improved QDs size homogeineity. The average indium content calculated from the out-plane HRXRD in samples A–D were 0.234%, 0.288%, 0.241%, and 0.218%, respectively. From the growth model, we noticed a significant change in the surface self-diffusion rate of indium adatoms. The indium adatoms migration to larger adjacent QDs is higher when the pre-matured QDs lie within the critical distance (X; ~ 30nm). At X > 30nm, the QDs start strinking, thereby reducing the height of QDs. Thus, this paper shows how our growth method helps in optimizing the QDs homogeineity and increasing the QDs dimension.

Luminescence and structural properties of Gd 2 SiO 5 :Eu 3+ phosphors synthesized from the modified solid state method

Abstract This paper reports the preparation of Eu 3+ doped Gadolinium oxyorthosilicate (Gd 2 SiO 5 :Eu 3+ ) phosphor with different concentration of Eu 3+ (0.1–2.5 mol%) using the modified solid state reaction method. The synthesis procedure of the Gd 2 SiO 5 :Eu 3+ phosphor using inorganic materials such as Gd 2 O 3 , silicon dioxide (SiO 2 ), europium oxide (Eu 2 O 3 ) and boric acid (H 3 BO 3 ) as flux is discussed in detail. The prepared phosphor samples were characterized by using X-Ray Diffraction (XRD), Field Emission Gun Scanning Electron Microscopy (FEGSEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Photoluminescence (PL) and Thermoluminescence (TL). The Commission Internationale de l′Eclairage(CIE) coordinates were also calculated. The PL emission was observed in the 350–630 nm range for the Gd 2 SiO 5 :Eu 3+ phosphor. PL excitation peaks were observed at 266, 275, 312 and 395 nm while the emission peaks were observed at 380, 416, 437, 545, 579, 589, 607, 615 and 628 nm. The emission peak at 615 nm was the most intense peak for all the different Eu 3+ concentration samples. From the XRD data, using the Scherrer's formula, the average crystallite size of the Gd 2 SiO 5 :Eu 3+ phosphor was calculated to be 33 nm. TL was carried out for the phosphor after both UV and gamma irradiation. The TL response of the Gd 2 SiO 5 :Eu 3+ phosphor for the two different radiations was compared and studied in detail. It was found that the present phosphor can acts as a single host for red emission (1.5 mol%) for display devices and light emitting diode (LED) and white light emission for Eu 3+ (0.1 mol%) and it might be used as a TL dosimetric material for gamma dose detection.

Photoluminescence excitation spectra of lanthanide doped YAlO3 in vacuum ultraviolet region

To understand luminescent mechanisms of lanthanide (Ln) doped phosphors, it is important to know the energy positions of unoccupied Ln2+ 4f and Ln3+ 5d states, as well as occupied Ln3+ 4f states, relative to the energy bands of host materials. Photoluminescence excitation (PLE) spectra of Ln doped YAlO3 were measured in a vacuum ultraviolet (VUV) region and the energy positions of Ln2+ 4f and Ln3+ 5d states in the wide-gap YAlO3 were elucidated. Peaks assignable to host lattice excitation were observed in all samples at approximately 8 eV in the PLE spectra. PLE peaks derived from charge transfer (CT) and 4f-5d transitions were observed at lower energy than the bandgap energy. Ln2+ 4f energy levels were obtained from the PLE peak energies for the CT transitions along with the valence band maximum. In contrast, Ln3+ 5d energy levels were evaluated from those for the 4f-5d transitions along with the Ln3+ 4f energy levels, which were obtained previously from X-ray photoelectron spectroscopy measurements. The elucidated Ln2+ 4f and Ln3+ 5d energy levels were exhibited in an energy diagram together with Ln3+ 4f energy levels and host energy bands. The experimental Ln2+ 4f and Ln3+ 5d energy levels were in good agreement with the reported theoretical data.

Facile preparation of YAG:Ce nanoparticles by laser irradiation in water and their optical properties.

Yttrium aluminum oxide Y3Al5O12 (YAG:Ce) nanoparticles were prepared by laser ablation in liquid, and the photoluminescence (PL) properties of the nanoparticles were investigated. A pellet of YAG:Ce synthesized by co-precipitation in deionized water was irradiated with a focused laser beam to obtain a solution containing dispersed nanoparticles. The compositions and morphologies of the nanoparticles were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis, and dynamic light scattering. PL and photoluminescence excitation (PLE) spectra at room temperature and low temperature were measured using a fluorescence spectrophotometer. Nanoparticles of YAG single phase as a matrix were obtained by irradiation at high laser energy density. The average particle size was approximately 9 nm, although the nanoparticles were slightly aggregated. The broad peak centered at 540 nm in the PL spectrum was asymmetrically broadened at shorter wavelength. The intensity of the PLE peak centered at 340 nm decreased with increasing energy density of the laser beam. These phenomena were related to the nanosize effect of the YAG:Ce phosphor.

Editors' Choice—Investigation of Luminescence and Photoacoustic Properties in Ce3+-Doped Ln3Al5O12 (Ln = Lu, Y, Gd) Garnet

Optical and photoacoustic properties of Ce3+-doped lanthanide (Lu, Y, Gd) aluminum garnet were investigated. In the photoacoustic (PA) spectra, the 5d1 (lowest 5d level) band of Ce3+ was observed at around 450 nm in the obtained Ce3+-doped garnet samples. This result shows that a part of the excited energy is converted to thermal energy, which is generated by some nonradiative processes. In Y3Al5O12:Ce3+, the 5d1 PA peak wavelength is shorter than the 5d1 photoluminescence excitation peak wavelength, which indicates that part of the heat generation is caused by the phonon relaxation process within 5d1 state. The PA intensity and luminescence quantum efficiency of the Ce3+-doped gadolinium yttrium aluminum garnets ((Gd0.5Y0.5)3Al5O12, (Gd0.75Y0.25)3Al5O12) are much stronger and smaller, respectively, than those of Y3Al5O12:Ce3+. Based on these results and the persistent luminescence excitation spectra, we conclude that (Gd0.5Y0.5)3Al5O12:Ce3+ and (Gd0.75Y0.25)3Al5O12:Ce3+ possess the additional heat generation process explained by the thermal ionization.

Luminescent properties of Dy3+ - doped CaMgSi2O6 phosphor

Photoluminescence (PL), mechanoluminescence (ML) and thermoluminescence (TL) studies of Dy3+-doped CaMgSi2O6 phosphor are reported in the present paper. The sample of CaMgSi2O6:Dy3+ was prepared by using a solid-state reaction method, where it was sintered at 1000 °C for 3 hour in a reducing atmosphere. The phosphor was characterized by using X-ray Diffraction (XRD), Energy dispersive X-ray (EDX) Spectroscopy, PL, TL, and ML measurement. From the X-ray diffraction pattern the phosphor was in a single-crystalline phase, and the average particle size of the CaMgSi2O6:Dy3+ phosphor was obtained as 44.15 nm from the peak corresponding to the (221) plane. The EDX spectroscopy confirmed the proper preparation of the sample. The afterglow of the sample exposed to ultraviolet (UV) radiation at 254 nm for 2 min could be seen for 30 min. The PL excitation peaks were found at 289 and 350 nm, and the CaMgSi2O6:Dy3+ phosphor showed three emission bands, with peaks at around 480 nm, 576 nm and 669 nm, respectively. From the TL glow curve, the activation energy was found to be 1.27 eV. The ML intensity increased linearly with increasing impact velocity of the piston used to deform the phosphor. The local piezoelectricity-induced electron bombardment model was shown to be able to interpret the ML emission well.

Lanthanide 4f energy levels in perovskite-type YAlO3

Based on experimental data, an energy diagram of 4f levels of lanthanide ions in perovskite-type YAlO3 was made to obtain fundamental knowledge of luminescence in trivalent lanthanide ions (Ln3+) doped YAlO3, YAlO3:Ln3+. Energy of valence band maximum (VBM) in YAlO3 and energies of Ln3+ 4f ground levels from VBM were determined by X-ray photoelectron spectra of non-doped YAlO3 and YAlO3:Ln3+ (Ln=Pr, Eu, Gd, Tb, Lu). Energies of Ln3+ 5d band were determined from the energy position of each photoluminescence excitation (PLE) peak attributed to 4f–5d transition. Energies of 4f ground levels of divalent lanthanide ions (Ln2+) were determined from the PLE peak of Eu3+ charge transfer states. Ln3+ 4f ground/excited levels, Ln2+ 4f ground levels, Ln3+ 5d bands, VBM and conduction band minimum were exhibited in the energy diagram setting the VBM at 0eV. Luminescence of several YAlO3:Ln3+ was discussed referring to the diagram.

Sodium doping in ZnO crystals

ZnO bulk single crystals were doped with sodium by thermal diffusion. Positron annihilations spectroscopy confirms the filling of zinc vacancies, to >6 μm deep in the bulk. Secondary-ion mass spectrometry measurement shows the diffusion of sodium up to 8 μm with concentration (1–3.5) × 1017 cm−3. Broad photoluminescence excitation peak at 3.1 eV, with onset appearance at 3.15 eV in Na:ZnO, is attributed to an electronic transition from a NaZn level at ∼(220–270) meV to the conduction band. Resistivity in Na doped ZnO crystals increases up to (4–5) orders of magnitude at room temperature.