Blue Luminescence Centers Research Articles

Oxygen Vacancies in Zirconium Oxide as the Blue Luminescence Centers and Traps Responsible for Charge Transport

The origin of luminescence centres and traps of charge carriers in ZrO2 was studied using Raman scattering, luminescence spectroscopy, charge transport and quantum-chemical calculation. After the X-ray irradiation of the ZrO2 film, the EPR spectra from an interstitial oxygen and a negatively charged oxygen vacancy are observed. The 2.7 eV luminescence band and 5.2 eV absorption/luminescence excitation band are associated with an oxygen vacancy. Half of the Stokes shift in blue photoluminescence spectra is equal to the trap thermal activation energy 1.25 eV estimated from the charge transport experiment. Within quantum-chemical simulations and experiments on the extraction of minority carriers from silicon substrates, it was demonstrated that both electrons and holes can be trapped on oxygen vacancies in ZrO2. Hence, oxygen vacancies are supposed to operate as traps responsible for the blue luminescence band and charge transport in ZrO2.

Color‐tunable and white emission of Tm3+ doped transparent zinc silicate glass‐ceramics embedding ZnO nanocrystals

AbstractTm3+ doped zinc silicate glass‐ceramics composed of SiO2‐Al2O3‐ZnO‐K2O‐Tm2O3 embedded with ZnO nanocrystals were successfully fabricated by melt‐quenching method with subsequent heat treatment. Tm3+ ions and ZnO nanocrystals were introduced as blue and yellow luminescence centers, respectively. The effects of heat treatment, excitation wavelength and Tm3+ doping concentration on the photoluminescence behaviors of these glass‐ceramics were studied. Short‐time (5 minutes) heat treatment was considered as the optimal heat treatment time, which facilitates simultaneously emitting narrow blue peak located at 453 nm and a broad yellow band centered at 580 nm. Blue and yellow emissions could be attributed to the 1D2 → 3F4 transition of Tm3+ and Zni/Oi‐related defect emission of ZnO nanocrystals, respectively. The combination of these two emissions allows the realization of white light emitting in the glass‐ceramic samples. Furthermore, tunable luminescent color and chromaticity coordinates, including yellow, white and blue, can be realized by varying the pumping wavelengths as well as the content of Tm3+ dopant in the glass matrix. Nearly perfect white light emission with Commission Internationale de l'Eclairage coordinate (x = 0.33, y = 0.32) was achieved for the 0.05 mol% Tm3+ doped glass‐ceramic embedding ZnO nanocrystals by heat treatment at 750°C for 5 minutes under the excitation of 360 nm. These luminescent glass‐ceramics doped with Tm3+ ion and ZnO nanocrystals could be a promising candidate for white light emitting devices under near‐ultraviolet excitation.

Thermal transformations in ZnS in the course of doping with CuCl

The photoluminescence, electroluminescence, and electron paramagnetic resonance spectra of ZnS powders thermally doped with CuCl are investigated. The processes occurring in the material during simultaneous annealing of ZnS and CuCl are discussed, and the influence of the annealing conditions on the formation of the CuS and Cu2S phases in zinc sulfide is analyzed. It is shown that the concentration ratio of the blue luminescence centers to the green luminescence centers and the concentration of Mn2+ paramagnetic centers in the phosphor prepared can be controlled by varying the rate of heating of the material to the annealing temperature. A technique based on low-temperature annealing is conceptualized and developed for synthesizing materials that, as rule, can be produced only through high-temperature annealing.

Distribution of Blue and Green Luminescence Centers in Barrier Regions of the Grains of Zinc Sulfide Electroluminophors

Based on the investigation of the spectra of two-photon excited luminescence of powder zinc sulfide electroluminophors, their electroluminescence spectra measured under different conditions at different stages of degradation, and also the data known from the literature dealing with the study of the microstructure of ZnS:Cu crystals, a conclusion has been drawn that the centers of green and blue luminescence are nonuniformly distributed over the luminophor grains. It is presumed that close by the surface of the grains, near the “second phase–zinc–sulfide” interface (the regions of energy barriers responsible for impact multiplication of charge carriers in prebreakdown electroluminescence) the centers of green luminescence predominate, while the blue luminescence centers are located at the periphery of the barriers, in deeper regions of the crystals.

Comparison of blue and red TL from quartz

Following a suggestion by Scholefield and Prescott that blue and red emissions in quartz may involve the same electron traps, we have made a detailed study of blue and red TL glow peaks in some Australian sedimentary quartz samples (Scholefield, R.B., Prescott, J.R., 1999. The red thermoluminescence of quartz: 3-D spectral measurements. Radiat. Meas. 30, pp. 83–95). Allowing for thermal quenching of the blue TL, the Rapidly Bleaching Peak (at 325°C for a ramp rate of 20 K s −1) and the low temperature peaks at 140–220°C appear to be identical in the blue and red. We conclude that the electron traps are the same, but that the blue and red luminescence centers probably do not occur in the same grains. On present evidence we cannot determine whether or not the Slowly Bleaching Peak (at 375°C for 20 K s −1) involves the same traps in the blue as in the red. As did Scholefield and Prescott, we find no evidence of a red peak at 100°C.

The energy transfer to the luminescence centers in PbWO4

The luminescence spectra, rise and decay kinetics and the yield of luminescence in undoped PbWO4 crystals were studied after pulsed electron beam irradiation. The luminescence intensity rise observed after irradiation pulse showed two mechanisms—excitonic relaxation and electron–hole recombination—were involved in the formation of the excited states of the blue luminescence centers. It is proposed that the excited states of WO3 and WO2−4 luminescence centers were formed from some intermediate metastable state.

The structure of high-temperature blue luminescence centers in zinc selenide and mechanisms of this luminescence

The characteristic features of temperature quenching of the intensity of the edge luminescence bands of n-ZnSe crystals annealed in different media (vacuum, Zn, Se) are investigated a wide temperature range. A change in the mechanisms of high-temperature exciton luminescence in the short-wavelength region of the spectrum (443 nm) with increase in temperature of the crystal is observed. It is shown that the nature of temperature quenching of the long-wavelength edge luminescence band (458 nm) is evidence of dissociation of associative luminescence centers with increase in the sample temperature.

ChemInform Abstract: Growth and Luminescence Properties of Mg‐Doped GaN Prepared by MOVPE

Abstract(metal‐organic vapor phase epitaxy).

Growth and Luminescence Properties of Mg‐Doped GaN Prepared by MOVPE

Growth and luminescence properties of Mg‐doped prepared by metal‐organic vapor phase epitaxy, in which or is used as the Mg source gas, are reported for the first time. It was found that the Mg concentration in is proportional to the flow rate of the Mg source gas; the doping efficiency of Mg into is independent of the substrate temperature from 850° to 1040°C; and Mg in acts as an acceptor and forms blue luminescence centers. By using, an efficient near‐UV and blue LED can be fabricated.

Zn related electroluminescent properties in MOVPE grown GaN

A thin AlN buffer layer was proven to be effective on both sapphire A-face and sapphire C-face substrates for the preparation of high quality Zn-doped as well as undoped GaN. The nature of Zn-related luminescence centers and their density are strongly affected by growth conditions; especially by the substrate temperature, which must be lower than 950°C for the efficient formation of blue luminescence centers. Zn-doped GaN grown on a sapphire A-face was found to have a greater density of blue luminescence centers than that on a C-face, indicating that the A-face is superior to the C-face as a substrate.

Method for separating complex spectral curves and the nature of blue-luminescence centers in crystalline quartz

Method for separating complex spectral curves and the nature of blue-luminescence centers in crystalline quartz

Blue and Green Luminescence Centers of Electroluminescent ZnS:Cu Phosphors

Emission spectra, glow curves and infrared stimulation of electroluminescent ZnS:Cu phosphors were observed. In the emission at low temperatures, the green component is predominant in the low frequency electroluminescence, while the blue component is predominant in the photoluminescence and in the high frequency electroluminescence. The green component is also strong in intensities throughout the thermoluminescent process. The ration of the blue to green components in the stimulated emissions at low temperatures decreases with increasing the wavelength of the irradiating infrared. These results can be interpreted in terms of an energy model in which the Schön-Klasens and Lambe-Klick models are assumed for the green and blue luminescence centers, respectively.