Yellow Emission Band Research Articles

H2O-NH4+-Induced Emission Modulation in Sb3+-Doped (NH4)2InCl5·H2O.

Lead-based metal halide perovskites have received widespread attention for their promising application prospects in the field of lighting and display due to their excellent optical properties. However, the toxicity of lead may hinder their further commercial application. Herein, a zero-dimensional (0D) metal halide (NH4)2InCl5·H2O with an orthorhombic structure and the Pnma space group was produced. With doping with Sb3+, these products exhibit one highly efficient and wide yellow emission band (∼450-850 nm) in their photoluminescence (PL) spectra, which covers almost the entire visible spectral range at room temperature; however, they give two emission bands with long decay lifetimes (microseconds) at low temperature. Temperature-dependent steady-state PL, transient PL spectroscopy, temperature-dependent Raman spectra characterization, and theoretical band structure calculations confirm that the dual-band emission at low temperature originates from the dual vibronic levels of the self-trapped exciton (STE) in the hole-vibration state, whose vibration energy is related to the H2O-NH4+ connection in the valence band. This result proves that the vibronic state in STE formation involves both electrons and holes in the excited states, the opposite of this happens in the electron-vibration band in most perovskite halides. These results provide new insight into the luminescent mechanism of Sb3+ in halide perovskites, especially used for emission color modulation by the temperature-dependent electron- or hole-vibration processes.

Broadband Yellow Phosphor Discovered by Single-Particle Analysis Based on Fluorescence Microscopy, Scanning Electron Microscopy, Cathodoluminescence, and Energy-Dispersive X-ray Spectroscopy.

The discovery of new, efficient, and stable inorganic phosphors excited by near-ultraviolet (n-UV) light is of great significance for the realization of high-performance healthy lighting and special lighting. The traditional methods to find new phosphors are usually time-consuming, laborious, and inefficient. Here, a simple and efficient method to find new phosphors using fluorescence microscopy, scanning electron microscopy (SEM), cathodoluminescence (CL), and energy-dispersive X-ray spectroscopy (EDS) is proposed. At the same time, a phosphor Ca5BaP4O16 (CBPO): Eu2+ found by this method is reported. Under 365 nm excitation, the optimal phosphor shows an ultrabroad yellow emission band with a peak at 573 nm and a full width at half-maximum of 164 nm. Compared with most phosphate phosphors, CBPO: Eu2+ shows good thermal stability. The emission intensity at 150 °C can maintain 61.4% of the initial value at room temperature. Importantly, the quantum efficiency of the optimal CBPO: Eu2+ sample is 66.2%. In addition, a WLED lamp was obtained by combining CBPO: Eu2+ and BAM: Eu2+ phosphors with a 365 nm n-UV chip, which generated high-performance white light with a correlated color temperature of 7115 K and a color rendering index of 89.4. It is certain that the new method is very effective and useful for the discovery of new phosphors.

Correlating yellow and blue luminescence with carbon doping in GaN

Blue and yellow emission bands in carbon-doped GaN grown by MBE were investigated in low-temperature cathodoluminescence measurements performed in a scanning transmission electron microscope (STEM-CL) with high spatial resolution. Blue luminescence at 2.85 eV and two contributions in the spectral range of the yellow emission band around 2.2 eV separated by 120 meV are observed in carbon-doped material, whereas only one distinctive yellow luminescence contribution was found in unintentionally-doped GaN.

Enhancement of optical property and crystal structure for GaN films on 2D MoS2 buffer layer by nitridation treatment

The growth of GaN films on layered 2D-MoS2/c-sapphire substrate by plasma-assisted molecular beam epitaxy system was investigated. Pre-nitridation process and deposition time as growth parameters were employed to exploit the heteroepitaxial growth of GaN films at the temperature of 700 °C. The characterizations of surface condition, surface morphology, chemical composition, optical properties, crystal orientation and quality of GaN epitaxial layers were conducted by reflection high energy electron diffraction (RHEED), scanning electron microscope (SEM), atomic force microscope (AFM), X-ray photoelectron Spectroscopy (XPS), Raman spectroscopy, photoluminescence spectroscopy (PL) and high-resolution X-ray diffraction (HR-XRD), respectively. The pre-nitridation process and growth duration can enhance the optical properties and crystal quality of GaN films on 2D-MoS2/c-plane sapphire. The pre-treatment of MoS2 layer by nitrogen plasma before the growth, providing a wetting layer of nitrogen for GaN growth, can eliminate the oxygen contamination and reduce the defects in the films. Band-to-band emission of Wurtzite GaN with the bandgap of 3.5 eV can be improved by pre-nitridation process, and yellow band emission can be suppressed due to the elimination of defect states in the films. Meanwhile, the crystal orientation and quality can be improved by the pre-nitridation process and longer duration of growth time. This study demonstrates a van der Waals epitaxial GaN films on 2D-MoS2 layer with higher crystal quality by pre-nitridation process, and it provides a potential solution for the future applications of GaN-based devices.

Blue-light-excitable broadband yellow-emitting CaGd2HfSc(AlO4)3:Ce3+ garnet phosphors for white light-emitting diode devices with improved color rendering index

The current commercial white light-emitting diodes (LEDs) are generally based on the combination of blue LED chips and Y3Al5O12:Ce3+ yellow phosphors. However, because of the lack of red component, such white LED devices exhibit cool white-light emissions with low color rendering index (Ra < 75, R9 < 0). Therefore, it is urgent to discover new blue-light-excitable yellow-emitting phosphors with enhanced red emissions for fabricating high color-quality white LEDs. In the present work, we demonstrate a novel broadband yellow-emitting CaGd2HfScAl3O12:Ce3+ garnet phosphor for blue-light-excited white LEDs with improved color rendering index. The as-prepared CaGd2HfScAl3O12:Ce3+ garnet phosphor possesses a cubic structure with Ia3¯d space group, and the unit cell parameters of the representative CaGd2HfScAl3O12:2%Ce3+ phosphor are a = b = c = 12.450 Å, α = β = γ = 90°, and V = 1,929.59(4) Å3. Impressively, we find that the CaGd2HfScAl3O12:Ce3+ garnet phosphor shows an intense absorption band in the 300–500 nm wavelength range with a maximum at 452 nm owing to the 4f→5d transition of Ce3+ ions. On 452 nm excitation, the optimal CaGd2HfScAl3O12:2%Ce3+ sample exhibits a broad asymmetric yellow emission band in the wavelength range of 470–750 nm with peak at 564 nm and full width at half maximum of 151 nm. The Commission Internationale de l’Eclairage chromaticity coordinates and internal quantum efficiency of the CaGd2HfScAl3O12:2%Ce3+ sample are (0.4485, 0.5157) and 30.4%, respectively. Finally, a white LED device is fabricated by combing a 450 nm blue LED chip with commercial Y3Al5O12:Ce3+ yellow-emitting phosphor, which generates white light with low color rendering index (CRI; Ra = 74.7, R9 = −12.7) and high correlated color temperature (CCT = 6,554 K) under the 60 mA driving current. In sharp contrast, another white LED device, which is made by coating our as-prepared CaGd2HfScAl3O12:2%Ce3+ yellow-emitting phosphors onto the surface of a 450 nm blue LED chip, produces white-light emission with high CRI value (Ra = 84.5, R9 = 26.3) and relatively low CCT of 5,649 K. This work reveals that the newly discovered broadband yellow-emitting CaGd2HfScAl3O12:Ce3+ phosphors can serve as a potential color converter in high-color-quality phosphor-converted white LEDs.

A novel rare-earth luminescent coordination polymer showing potential semiconductor characteristic constructed by anthracene-based dicarboxylic acid ligand (H2L)

• A new member of rare-earth coordination polymer based on H 2 L was successfully synthesized using a solvothermal method. • The crystal structure, morphology feature and thermostability of the obtained La-CP were systematically characterized and analyzed by a series of measurement techniques. • La-CP exhibited a yellow fluorescence emission band with a QY of 1.81%. • Its semiconductor characteristic was confirmed by the optical band gaps from DRS data as well as the electronic structure calculation. In this study, one new rare-earth lanthanum(Ⅲ) metal-organic coordination polymer {[La(L) 1.5 (H 2 O)(DMF)]∙DMF} n (H 2 L = 4,4’-(diethynylanthracene-9,10-diyl) dibenzoic acid) labeled as La-CP was successfully constructed via a solvothermal process. Structure analysis of the obtained La-CP revealed that it crystallized in the triclinic space group P -1, in which each La 3+ ion was coordinated to eight oxygen atoms to form a distorted square antiprism geometry. It was important to observe π-π stacking between adjacent ligand moieties of La-CP with face-to-face distances of 3.385 and 3.447 Å, endowing charge carriers with the possibility of through-space transport. The optical band gap of 2.23 eV evaluated from the UV-vis diffuse reflectance spectrum, coupled with electronic band structure calculation, provided reliable evidence of its potential semiconductor characteristic. In addition, La-CP exhibited a yellow fluorescence emission and a comparable quantum yield of 1.81% to that of free ligand H 2 L in terms of its optical properties. This work not only expands the list of rare-earth lanthanide coordination polymers but also offers useful guidance for materials design and related properties modulation of coordination polymers to some extent.

Dual-Emitting Carbonized Polymer Dots Synthesized at Room Temperature for Ratiometric Fluorescence Sensing of Vitamin B12.

Ratiometric fluorescence (FL) probes are highly desirable for highly sensitive and reliable assays. Dual-emitting carbonized polymer dots (CPDs) have great application prospects in building ratiometric FL sensors. However, dual-emitting CPDs are usually synthesized at high temperatures and high pressures, which not only increases the cost but also complicates the structure of CPDs. Here, we developed a facile strategy for the fabrication of dual-emitting CPDs at room temperature using tetrachlorobenzoquinone and ethylenediamine. The formation of CPDs was induced by Schiff base condensation reaction, enabling the following cross-linking polymerization process. The dual-emitting CPDs demonstrate good photostability and antioxidant capacity. Importantly, the typical dual-emission bands of the as-prepared CPDs are found to have a blue emission band at 445 nm with a maximum excitation of 350 nm and a yellow emission band at 575 nm with a maximum excitation of 440 nm. Based on the dual-emitting property of CPDs, a ratiometric FL nanoprobe is obtained for sensitive determination of vitamin B12 (VB12), as the inner filtering and static quenching effects between VB12 and CPDs allow effective quenching of the blue FL of CPDs, while the yellow FL is maintained. The established assay shows linear detection ranges of 0.25-100 μM with a low limit of detection of 0.14 μM. These findings provide new guidance for the facile preparation of CPDs with excellent dual-emitting optical properties, indicating good prospects in biosensing.

Chlorinated yellow phosphorescent cyclometalated neutral iridophosphors featuring broad emission bandwidths for white electroluminescence

The efficient yellow phosphors with broad emission bandwidths play quite important roles in the realization of high-performance two-color white organic light-emitting devices (OLEDs). Herein, by using a chlorine-functionalization method, we designed three efficient yellow iridium(III) complexes (Ir1–Ir3) bearing chlorine atoms. At room temperature, these phosphors exhibit bright yellow phosphorescence with emission wavelengths of 549–574 nm and high photoluminescence efficiency of 0.49–0.73 in the N2-saturated dichloromethane. Importantly, these complexes feature extremely broad emission bandwidths (reaching 104 nm), making them the record-high values in the yellow iridium(III) phosphors reported so far. Using these complexes as the triplet dopants, the prepared OLEDs show yellow phosphorescence with the emission maximum at 565, 548, and 551 nm, respectively. The extremely high external quantum efficiency of 23.8% was realized for the as-prepared yellow OLEDs. Furthermore, Ir2-based two-color white OLED with high spectral quality was also realized, and the color rendering index and CIE coordinates for two-color white OLED are 74 and (0.32, 0.34), respectively. The broad yellow emission band and high-efficiency of the device proved that these phosphors show great potentials in developing high-performance yellow and white electroluminescence.

Insight into the crystal structure and photoluminescence properties of an extremely broadband yellow-emitting phosphor Sr8MgCe(PO4)7:Eu2.

The combination of binary complementary color phosphors with near-ultraviolet (NUV) light-emitting diode (LED) chips was put forward to lower the energy loss caused by the reabsorption of the combination of tricolor phosphors with NUV LED chips. Thus investigating broadband yellow-emitting phosphors with enriched red components in the spectral range has gained much attention. Here, an extremely broadband yellow-emitting phosphor Sr8MgCe(PO4)7:Eu2+ with sufficient red component in the spectral region was synthesized. Due to the introduction of Ce into the host, Sr8MgCe(PO4)7 shows an emission band with a peak at 375 nm when excited at 310 nm. Meanwhile, Eu2+ doped Sr8MgCe(PO4)7 exhibits an extremely broad yellow emission band with a full width at half-maximum of 175 nm and a peak located at about 598 nm, due to the 5d-4f transitions of Eu2+ ions substituting five Sr2+ sites. The excitation peak of the host at 310 nm was detected in the excitation spectrum of Sr8MgCe(PO4)7:Eu2+ monitored at 598 nm, indicating the energy transfer from the host to Eu2+, which was also proved by the decay curves. On the other hand, the excitation band at about 400 nm due to the 4f-5d transitions of Eu2+ was also detected in the excitation spectrum of Sr8MgCe(PO4)7:Eu2+, and this matches well with the NUV LED chips. Moreover, the energy transfer between Eu2+ ions at different crystallographic sites was demonstrated by time-resolved photoluminescence (TRPL) spectra. A white LED with a CRI (Ra) of 82.88 and a CCT of 4238 K was prepared through a 400 nm NUV LED chip, Sr8MgCe(PO4)7:Eu2+ and BaMgAl10O17:Eu2+ (BAM:Eu2+). These results pave the way for designing better Eu2+-doped phosphors for NUV WLEDs with binary complementary color phosphors.

Crystal Structure and Photophysical Properties of a Novel Dy-Hg Isonicotinic Acid Compound with One-Dimensional Chain-Like Cations

A novel Dy-Hg compound [Dy(HIA)3(H2O)2]2n · 2nHgCl4 · nHgCl5 · nH3O · 3nH2O (1; HIA = isonicotinic acid) was prepared through a hydrothermal reaction and characterized by X-ray diffraction. The compound crystallizes in the space group of C2/c of the monoclinic system. The crystal structure of compound 1 has one-dimensional (1-D) chain-like cations. A photoluminescence experiment with a solid-state sample revealed that this compound exhibits a yellow emission band at 575 nm and, this emission band shall come from the 4f electron 4F9/2 → 6H13/2 characteristic transfer of Dy3+ ions. The compound features CIE chromaticity coordinates of 0.5168 and 0.4824 in the yellow region. A UV-visible diffuse reflectance spectrum with a solid-state sample unveiled that this compound possesses a wide optical band gap of 3.39 eV.

J-O study of a novel Dy-doped Lu3Al5O12 transparent ceramic for potential application in yellow laser generation

A novel Dy:LuAG transparent ceramic was fabricated by a solid-state method, and it has the potential to be used as the gain medium of yellow laser generated by blue LD pumping. The spectroscopic parameters were determined by the Judd-Ofelt theory, and Ω2, Ω4, Ω6 were calculated to be 0.57 × 10−20 cm2, 1.44 × 10−20 cm2, 0.68 × 10−20 cm2, respectively. An intense yellow emission band, corresponding to the 4F9/2 → 6H13/2 transition located at 581 nm, was observed in the visible region. The non-exponential curve was fitted to the Inokuti–Hirayama model to understand the energy-transfer mechanism. The fluorescence lifetime of the 4F9/2 level was about 339 μs, and the quantum efficiency was 21.7%.

Defect-related optical properties of Mg-doped ZnO nanoparticles synthesized via low temperature hydrothermal method

In this work, the monodispersed Mg-doped ZnO (Zn1-xMgxO, x = 0–0.06) nanoparticles (NPs) were synthesized through low temperature hydrothermal method. The as-prepared Zn1-xMgxO NPs exhibited single hexagonal wurtzite structure, confirming the incorporation of Mg2+ into ZnO lattice by replacing the Zn2+ ions. Optical analyses suggested the optical band gap of Zn1-xMgxO NPs increased from 3.46 to 3.59 eV with increasing Mg content from 0 to 0.06. The photoluminescence (PL) spectra of undoped and Mg doped ZnO NPs showed strong and broad visible emissions. With increasing Mg2+ content, the PL peak energy, intensity, and PL lifetime increased. The broad visible emission band was consisted of green, yellow, and red emission bands associated with different defect states. Based on the Mg content- and the temperature-dependent PL spectra, we proposed the possible origin of the observed visible emissions, which can be favorable for further understanding the correlation between the lattice states and PL property of doped ZnO NPs.

Visible emission studies of melt-grown Dy-doped CsPbCl3 and KPb2Cl5 crystals

We report results of the optical properties of Dy-doped CsPbCl3 and KPb2Cl5 bulk crystals for potential applications in yellow solid-state laser development. The crystals were synthesized from purified starting materials and melt-grown by vertical Bridgman technique. Optical transmission measurements revealed characteristic absorption bands from intra-4f transitions of Dy3+ ions. Direct optical excitation at 455 nm (6H15/2 → 4I15/2) resulted in dominant yellow emission bands at ∼575 nm from the 4F9/2 excited state of Dy3+ ions. In addition, both crystals exhibited weaker emission lines in the blue (∼483 nm) and red (∼670 nm) regions. The peak emission-cross sections for the yellow transition (4F9/2 → 6H13/2) were determined to be ∼0.22 × 10−20 cm2 for Dy: CsPbCl3 (λpeak = 576.5 nm) and ∼0.59 × 10−20 cm2 for Dy: KPb2Cl5 (λpeak = 574.5 nm). The spectral properties and decay dynamics of the 4F9/2 excited state were evaluated within the Judd-Ofelt theory to predict total radiative decay rates, branching ratios, and emission quantum efficiencies.

Photoluminescent properties of ZnO nanorods films used to detect methanol contamination in tequila

Zinc oxide (ZnO) nanorod films with thickness of 700 nm were prepared via a chemical bath deposition method using a ZnO seed layer deposited on a silicon substrate by a conventional dip-coating technique. The morphology and structural properties of the obtained ZnO nanorods were characterized by field emission scanning electron microscopy and Raman spectroscopy. Photoluminescence spectroscopy exhibited an intense emission located at 380 nm related to near band edge (NBE) recombination and a yellow emission band at 575 nm attributed to intrinsic defects of ZnO. Changes in intensity of the NBE and yellow emissions were determined through room-temperature photoluminescence measurements of ZnO nanorods films when exposed to vapors of ethanol, methanol and tequila-methanol mixtures respectively. ZnO nanorods based sensors showed rapid response times and moderate recovery times together with good selectivity for methanol and ethanol vapors. For tequila-methanol mixtures samples, the change in photoluminescence intensity of both said emissions of ZnO nanorods presented an opposite behavior in comparison against methanol and ethanol samples. Intensity changes of the NBE emission showed a linear trend depending on the increase in methanol concentration, while the yellow emission intensity presented an exponential trend for concentrations below 50 % of methanol in tequila.

Influence of high gamma radiation on the optical and photoluminescence characteristics of ZnO thin films

In this study, the researchers attempt to investigate the effect of irradiation of gamma doses in the range 25–150 kGy on the optical properties of sputtered ZnO thin films. The samples have a hexagonal wurtzite structure. The optical properties of the samples, such as the absorbance, transmittance, and reflectance, have been studied as a function of γ- irradiation doses. Several optical parameters, such as refractive index, optical energy gap, Urbach energy, oscillatory energy, dispersion energy, oscillator strength, and dielectric constant have been found to be affected by changing the γ- irradiation doses. The refractive index dispersion curve of the γ-irradiated and non-irradiated ZnO thin films meet the criteria of the single-oscillator model. The room temperature photoluminescence spectra of the samples under excitation 400 and 437 nm showed green emission nearly at 2.597 and 2.559 eV, and yellow emission approximately at 2.15 eV. The green emission bands can be attributed to a transition from CB to VZn −2 and −1 respectively, while the yellow emission band can be attributed to a transition between a shallow donor and a deep level.

Synthesis of RE3+ (RE3+ = Ce3+, Dy3+, Eu3+ and Tb3+) activated Gd2SiO5 optoelectronics materials for lighting

RE3+(RE3+ = Ce3+, Dy3+, Eu3+ and Tb3+) doped Gd2SiO5 optoelectronic materials were synthesised by solid state diffusion method and their down conversion spectral properties were reported in this paper as function of different RE3+ concentrations. The solid state diffusion results in well crystallized phosphor particles. The prepared materials were characterized by XRD, FT-IR, photoluminescence (PL) and CIE color co-ordinates techniques. Spectroscopic investigation revealed that gadolinium oxyorthosilicate (GSO), Gd2SiO5 phosphor doped with Ce3+ shows broad band emission with peak at 390 nm and 440 nm when excited at 350 nm excitation. Gd2SiO5:Dy3+ shows efficient blue and yellow band emissions at 481 nm and 576 nm Gd2SiO5:Eu3+ phosphor shows an orange and red emission at 587 nm and 615 nm respectively. Whereas Gd2SiO5:Tb3+ phosphor shows weak blue emission at 487 nm and strong green 545 nm. The excitation spectra used for the Gd2SiO5:RE3+ (where RE3+ = Ce3+, Dy3+, Eu3+ and Tb3+) phosphor are in the near UV (nUV) region extending from 250 to 400 nm, which is characteristics of modern lighting and display fields applications. The effect of the RE3+ (RE3+ = Ce3+, Dy3+, Eu3+ and Tb3+) concentration on the luminescence properties of Gd2SiO5:RE3+ optoelectronics materials were also studied. The investigated prepared Gd2SiO5 phosphors may be suitable for lighting based devices.

Raman and Photoluminescence Study of Al,N‐Codoped ZnO Films Deposited at Oxygen‐Rich Conditions by Magnetron Sputtering

Optical properties of as‐grown high nitrogen‐doped ZnO:Al,N films (with a variation of nitrogen concentration from 2.3 to 4.3 atomic %) are studied by Raman, photoluminescence, and Fourier‐transform infrared spectroscopy (FTIR). The intensity of mode A1LO, peaked at 580 cm−1, increases with increasing nitrogen concentration. The silent mode B1low at 275 cm−1 is clearly observed testifying increased disorder‐activated scattering in ZnO. Photoluminescence spectra reveal near‐band edge emission as well as several defect‐related bands, the intensity of which increases with nitrogen content. The blue band (2.61 eV) can be related to the transition from shallow donor level to deep nitrogen acceptor level. Also, incorporation of nitrogen in ZnO lattice causes appearance of both Zni and Oi defects responsible for violet (3.08 eV) and yellow (2.16 eV) emission band, respectively. At the same time near‐band edge emission of ZnO:Al,N films is not suppressed by simultaneously introduced Al and N impurities. Al compensates distortions in ZnO crystal lattice caused by nitrogen doping and, thus, stabilizes near‐band edge emission.

Phosphorescent cyanide sensor based on a 2-phenylpyridine(ppy)-type cyclometalated Ir(III) complex bearing dimesitylboron group with concentration distinguishing ability

With a 2-phenylpyridine(ppy)-type cyclometalated Ir(III) complex with –B(Mes)2 group Ir–B, the CN¯ ions can bind effectively with the boron atom in the –B(Mes)2 group to furnish CN¯ sensing ability through inducing phosphorescence changing of the concerned Ir(III) complex. Uniquely, with increasing the added amount of CN¯ ions, loose and tight binding between CN¯ and boron atom in the –B(Mes)2 group of Ir–B can occur in sequence to destabilize metal-to-ligand charge transfer (MLCT) excited states and then form new MLCT excited states in Ir–B. Accompanying this process, the red phosphorescence of Ir–B can be effectively quenched by adding CN¯ ions, while new yellow and green emission bands can appear in sequent with increasing the amount of added CN¯ ions, showing CN¯ sensing behavior with unique concentration distinguishing ability. In addition, the new phosphorescent CN¯ sensor can possess detection limit (DL) as low as 4.3 × 10−6 M and good selectivity to the CN¯ ions. Clearly, these results can provide important information for developing new CN¯ sensors with high performances.

Room-temperature photoluminescence of Mg-doped GaN thin films grown by plasma-assisted MOCVD

The growth of Mg-doped GaN thin films by metalorganic chemical vapor deposition (MOCVD) using NH3 and Cp2Mg as a source of nitrogen and Mg, respectively, usually produces Mg–H complexes, which hinder the activation of Mg as shallow acceptor centers. Therefore, post-growth treatments are commonly required to activate these acceptor centers. The presence of Mg dopants in GaN films induces various defect-related emissions whose characteristics depend on the growth method. For this study, we prepared Mg-doped GaN thin films by plasma-assisted MOCVD. A nitrogen-plasma, instead of NH3, served as a nitrogen source to minimize the formation of Mg–H complexes, thereby eliminating the requirement for post-growth treatment. The emission characteristics were obtained by measuring the photoluminescence of the as-grown room-temperature films. Yellow, green, blue, and ultraviolet emission bands are produced by Mg-doped samples with different Mg concentrations produced by Cp2Mg flow rates of 2%, 5%, and 10% of the total flow rate. Low-Mg concentration leads to nitrogen and gallium vacancies, which results in yellow photoluminescence. At higher Mg concentration, the yellow photoluminescence is suppressed and the blue photoluminescence is enhanced because of the incorporation of vacancies by Mg atoms. The analysis of the photoluminescence spectra leads to the proposed band diagrams for Mg-doped GaN with varying Mg concentration.

Site-Selective Occupation for Broadband Upconversion Luminescence in Ca3Y(GaO)3(BO3)4:Yb3+,Mn2+ Phosphors

Room-temperature yellow emission band around 600 nm is obtained in Yb3+ and Mn2+ codoped Ca3Y(GaO)3(BO3)4 with near-infrared laser excitation. The structure analysis, excitation and emission spectr...