Use In White Light-emitting Diodes Research Articles

Defect-Enabled Superior Negative Thermal Quenching in Palmierite Ba9La(VO4)7:Eu3+ for WLED In Situ Temperature Measuring.

Negative thermal quenching (NTQ) of the phosphors is critically important for both scientific research and practical applications, but the design of efficient NTQ phosphors is still a challenging task. Herein, we report a new strategy for developing NTQ materials by cation-vacancy engineering. Specifically, a new color-tunable Ba9La1-x(VO4):xEu3+ (BLVO:xEu3+) phosphor with abundant intrinsic cation vacancy was developed, exhibiting superior NTQ behavior under 365 nm excitation. The NTQ performance can be modulated via adjusting Eu3+ doping levels, and the emission intensity of Eu3+ ions in the BLVO:0.20Eu3+ phosphor increased by 275% at 473 K compared to room temperature. Furthermore, the reported material emitting bright white light under 365 nm excitation was well-suited for use in white light-emitting diode (WLED) phosphor and fluorescent temperature sensors, exhibiting outstanding color-rendering index (90.1) in lighting and high sensitivity (Sa = 11.83% K-1, Sr = 2.33% K-1) in temperature detecting. Lastly, the operating temperature of WLED at different currents can be monitored and displayed in real time through emission spectroscopy. All of the results demonstrated that the designed NTQ BLVO:xEu3+ can be used as a single-phase white phosphor and optical thermometry. This work provides a fresh perspective for designing high-efficient NTQ phosphors and expands the application of phosphors in WLED in situ temperature detection.

Effect of annealing temperature and doping concentrations on structure and optical properties of Eu3+-doped TiO2 nanomaterials

In this study, we successfully synthesized europium-doped TiO2 (TiO2:Eu3+) nanomaterials (NMs) with crystalline sizes ranging from 6.5 to 71.7 nm through a sol-gel method. Analysis of X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-Vis) spectra indicates that the substitution of smaller-sized Ti4+ ions (0.745 Å) by larger-sized Eu3+ ions (0.947 Å) was more efficient at higher doping concentrations and annealing temperatures. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the synthesized TiO2:7%Eu3+NMs exhibit a strong red emission band peaking at 613 nm and remarkable absorption in the blue light region centered at 463 nm, making them suitable for use in white light-emitting diode (WLED) applications. Our findings reveal that both annealing temperature and doping concentration significantly influence the structure and properties of these materials. Besides, the research team has seen, under the experimental conditions, the TiO2:7%Eu3+ sample annealed at 800°C exhibits the highest PL intensity. These results underscore the potential of the synthesized TiO2:Eu3+ NMs as red-emitting materials for WLED applications.

Unveiling Local Electronic Structures of Manganese‐Doped Double Perovskites Red Emitters

AbstractOver the past few years, light‐emitting diodes (LEDs) have emerged as an efficient replacement for standard incandescent and fluorescent lamps, due to their superior efficiency, energy conservation, service longevity, reliability, and affordability. However, identifying a red emitter for white LEDs has presented significant challenges. This study seeks to synthesize and analyze a novel red emitter, investigating its potential use in white LEDs and indoor plant growth lighting. The Sr2Lu(Nb,Mn)O6 is manufactured employing the traditional high‐temperature solid‐phase method. The internal and external quantum efficiencies (IQE and EQE) of double perovskites reached 32.39% and 21.67%. The g value calculates to 2.146, which corroborates that the magnetic dipolar transitions of Mn4+ ions inhabit symmetric octahedral sites. First‐principles investigations are utilized to unveil local electronic structures. Emission spectra reveal a substantial broad red emission peak at 688 nm. The Tanabe–Sugano diagram is applied to understand the luminescence mechanism. Additionally, the evaluation of parameters such as the internal UV emission ratio, crystal field strength, and Racah parameters is conducted. The luminescent intensity of the Sr2Lu(Nb,Mn)O6 can still be maintained at 60% upon reaching a temperature of 423 K. The findings suggest that Sr2Lu(Nb,Mn)O6 offers a novel alternative for white LEDs and indoor plant growth lighting.

Synthesis, luminescence properties, and thermal decomposition kinetics of NH4GdF4:Eu3+ with an intense negative thermal quenching effect

Developing Eu3+-doped red emission phosphors with exceptional luminescence thermostability is crucial for advancing white light emitting diodes (WLEDs). Herein, a series of NH4GdF4:xEu3+ (NGF:Eu3+) compounds are synthesized using the co-precipitation method, with NGF:0.25Eu3+ identified as the most promising sample. The paper discusses the mechanism underlying the negative thermal quenching (NTQ) effect, indicating that NGF:0.25Eu3+ exhibits sufficient luminescence thermal stability and chemical resistance under the operational temperatures of WLEDs, making it a viable application for this purpose. Experimental results reveal the following key findings. (a) Supported by the NTQ effect, NGF:0.25Eu3+ exhibits remarkable luminous thermostability. The integrated emission intensities at 150 °C, 180 °C, and 121 °C are 210.6 %, 234.1 %, and 244.2 % respectively, of the initial intensity at 30 °C. (b) NGF:0.25Eu3+ demonstrates good chemical thermostability and sufficient luminescent thermal stability under WLED operational temperatures and commences decomposition at 200 °C, making it suitable for use in WLEDs. (c) An assembled prototype WLED combining NGF:0.25Eu3+ and YAG:Ce3+ (a yellow emitting phosphor), emits warm white light under ultraviolet excitation. Furthermore, this study delves into the thermal decomposition kinetics of NGF:0.25Eu3+ using an iterative approach, identifying a single-step reaction mechanism. Consequently, the study provides three kinetic parameters (Eα, g(α), and A) and three thermodynamic functions (ΔH#, ΔS#, and ΔG#) associated with the decomposition process.

Luminescence properties of Eu2+ and Sm3+ co-doped in KBaPO4

Abstract KBaPO4:Eu2+/Sm3+ phosphor was synthesized via the high-temperature solid-phase reaction method. The structural properties, surface morphology, and optical properties of the synthesized samples were obtained by the X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and fluorescence measurements. The XRD patterns indicate that the crystal structure of KBaPO4 has not been changed by co-doped with two rare-earth ions. Under the excitation of 400 nm, the Eu2+ and Sm3+ co-doped KBaPO4 phosphors showed typical emission peaks at 430 (blue), 562 (yellow), and 600 nm (red). Meanwhile, with the increase of the Sm3+ content, the photoluminescent (PL) emission intensity of Sm3+ increased until the content reaches 0.12. However, the PL intensity of Eu2+ ions gradually decreased, which indicated that there was a possible energy transfer between the two ions. Therefore, the obtained results indicated that Eu2+/Sm3+ co-doped KBaPO4 is a promising phosphor for the use in white light-emitting diodes with near ultraviolet chips.

Lead-free Double Perovskite Cs2 AgIn0.9 Bi0.1 Cl6 Quantum Dots for White Light-Emitting Diodes.

Perovskite‐based optoelectronic devices have attracted considerable attention owing to their excellent device performances and facile solution processing. However, the toxicity and intrinsic instability of lead‐based perovskites have limited their commercial development. Moreover, the provision of an efficient white emission from a single perovskite layer is challenging. Here, novel electrically excited white light‐emitting diodes (WLEDs) based on lead‐free double perovskite Cs2AgIn0.9Bi0.1Cl6 quantum dots (QDs) without any phosphor are fabricated for the first time. Density functional theory calculations are carried out to clarify the mechanism of absorption and recombination in Cs2AgIn0.9Bi0.1Cl6 with Bi‐doping breaking the parity‐forbidden transition of the direct bandgap. Microzone optical and electronic characterizations reveal that the broadband emission of Cs2AgIn0.9Bi0.1Cl6 QDs originates from self‐trapped excitons, and luminescent properties are unchanged after the film deposition. The QD‐WLED exhibits excellent Commission Internationale de L'Eclairage color coordinates, correlated color temperature and relatively high color rendering index of (0.32, 0.32), 6432 K, and 94.5, respectively. The maximum luminance of 158 cd m−2 is achieved by triphenylphosphine oxide passivation, and this lead‐free QD‐WLED exhibits a superior stability in ambient air with a long T 50 ≈48.53 min. Therefore, lead‐free perovskite Cs2AgIn0.9Bi0.1Cl6 QDs are promising candidates for use in WLEDs in the future.

Encapsulating carbon quantum dot and organic dye in multi-shell nanostructured MOFs for use in white light-emitting diode

Abstract Encapsulating luminescence units into porous metal-organic frameworks to obtain white-light emission has attracted much attention because of their high designability and excellent color-tuning flexibility. In this study, two types of luminescence units with different emission color coverage, namely green-emitting carbon quantum dots (CQDs) and red-emitting rhodamine B (RhB) molecules, were encapsulated into porous ZIF-8 to obtain the yellow-emitting composite phosphor for use in white light-emitting diodes (LEDs). Single-phase single-shell CQDs&RhB@ZIF-82, as well as single-phase multi-shell CQDs@ZIF-82@RhB@ZIF-82, were fabricated and fine-tuned (by varying the amount of accommodated CQDs and RhB) so that the emitted color is near that of the commercial yellow-emitting phosphor. The multi-shell CQDs@ZIF-82@RhB@ZIF-82 has much better luminescence efficiency than that of the single-shell one. This is because the multi-shell structure provides a much larger separation distance of the encapsulated guest units, diminishing the energy-transfer-caused efficiency decrease. It is also shown that a bright source of white light can be realized by coating the CQDs@ZIF-82@RhB@ZIF-82 nanocomposite on a commercial blue (460 nm) LED chip.

Effect of Al3+ on the spectroscopic properties of Eu2+- and Tb3+-Doped high silica glass

In this study, Eu2+/Al3+-, Eu2+/Tb3+-, and Eu2+/Tb3+/Al3+-doped high silica glasses were prepared, and the effect of Al3+ on the spectroscopic properties of Eu2+ and Tb3+ and the energy transfer of Eu2+→Tb3+ was investigated. The results revealed that the addition of Al3+ increased the luminescent intensity of the Eu2+-doped glass by approximately 400 times. An obvious Eu2+→Tb3+ energy transfer occurred in the Eu2+/Tb3+-doped high silica glass, whose transfer efficiency can reached 66.9%. However, the efficiency continuously decreased as the Al3+ concentration increased, and eventually, it dropped to 7.2%. These phenomena can be explained by the following: Al3+ not only disperses Eu2+ but also changes the field strength and symmetry of its neighboring environment, thus increasing its emission intensity. Moreover, Al3+ destroys the strong dipole–dipole interactions between Eu2+ and Tb3+ in high silica glass due to its dispersive ability, which inhibits the energy transfer of Eu2+→Tb3+. This indicates that a small amount of Al3+ can significantly modify the neighboring environment of Eu2+ and change its light-emitting characteristics, potentially yielding efficient blue and green phosphors excited by near-ultraviolet light for use in white light-emitting diodes.

Optimization of structural and luminescent properties with intense red emitting thermally stable Sm3+ doped CaBiVO5 phosphors for w-LED applications

Sm3+ doped CaBiVO5 (CBV: Sm3+) phosphors synthesized namely by solid-state reaction (SSR), combustion (CB) and citrate sol-gel (SG) method to optimize the synthesis procedure and also to enhance the luminescent properties for the first time. X-ray powder diffraction patterns and scanning electron micrographs recorded for the synthesized CBV: Sm3+ phosphors to analyse structural and morphological aspects, respectively. The excitation spectra measured by monitoring emission at 649 nm for CBV: Sm3+ phosphors reveal significant absorption in ultraviolet (UV), near (n)-UV and blue spectral regions. The comparative photoluminescence (PL) spectra measured under 343 nm excitation for differently synthesized CBV: Sm3+ phosphors, which exhibit significantly enhanced emission intensity for SG derived phosphor than other adopted methods. The PL spectra for SG derived 1.0 mol% Sm3+ doped CBV phosphor at λex = 275 and 343 nm exhibit sharp peaks located at 566, 606 and 649 nm along with weak host emission broadband and for λex = 406 nm, similar sharp peaks of Sm3+ transitions are observed without any host emission. Unlike mostly explored Sm3+ doped phosphors, emission peak in red spectral region (649 nm) is more intense as compared to the emission peak in orange region (599 nm) in the present work. The energy transfer mechanism responsible for concentration quenching in CBV phosphors is discussed in detail. The CBV: Sm3+ phosphors manifest color tunability from orange to orange-red region by modulating excitation from 275 nm (0.567, 0.404) to 343 nm (0.591, 0.399) and finally to 406 nm (0.620, 0.376). The temperature-dependent PL studies indicate appreciable thermal stability of as-prepared phosphor. Above mentioned results suggest that CBV: Sm3+ phosphor has great potential for use in white light-emitting diode (w-LED) applications.

Photoluminescence and structural analysis of trivalent europium doped MLaAl3 O7 (M = Ba, Ca, Mg and Sr) nanophosphors.

The solution combustion technique was used to synthesize MLaAl3 O7 (M = Ba, Ca, Mg, and Sr) nanophosphors-doped with Eu3+ using metal nitrates as precursors. The photoluminescence (PL) emission spectra exhibited three peaks at 587-591, 610-616, and 653-654 corresponding to 5 D0 →7 F1 , 5 D0 →7 F2 , and 5 D0 →7 F3 transitions, respectively. Upon excitation at 254 nm, these nanophosphors displayed strong red emission with the dominant peak attributed to the 5 D0 →7 F2 transition of Eu3+ . The materials were further heated at 900 and 1050°C for 2 h to examine the consequence of temperature on crystal lattice and PL emission intensity. X-ray diffraction (XRD) analysis proved that all the synthesized materials were of a crystalline nature. CaLaAl3 O7 material has a tetragonal crystal structure with space group P421m. Scherer's equation was used to calculate the crystallite size of synthesized phosphors using XRD data. A Fourier transformation infrared study was used to observe the stretching vibrations of metal-oxygen bonds. Infrared peaks for stretching vibrations corresponding to lanthanum-oxygen and aluminium-oxygen bonds were found at 582 and 777 cm-1 respectively for CaLaAl3 O7 phosphor material. Transmission electron microscopy images were used to determine the size of particles (18-37 nm for the as-prepared materials) and also to analyze the three-dimensional view of these materials. The experimental data indicate that these materials may be promising red-emitting nanophosphors for use in white light-emitting diodes.

Engineering the optical properties of Cu doped CeO2 NCs for application in white LED

Cerium dioxide (ceria, CeO2) with wide band gap (3.6 eV) is optically transparent for visible light and efficiently luminescent in the UV-range. Here, we have investigated the effect of Cu dopant ions on the structural and optical properties of Ce1-xCuxO2; (0.00 ≤ x ≤ 0.20) nanocrystals (NCs) synthesized via co-precipitation technique. XRD results confirmed the successful incorporation of Cu ions into CeO2 single-phase cubic system. The decrease in the crystallite sizes (13 - 4 nm) as the Cu content increase indicates towards the decrease in the crystal quality and introduction of additional lattice defects. The concentration of oxygen deficiency (δ) and the reduction in the oxygen valency (CeO2-δ) have been evaluated quantitatively using Raman spectroscopy. The possible defects, assessed via Photoluminescence (PL) emission spectra, generate profound energy bands localized in the forbidden band region, which causes a lowering in the UV emission efficiency and narrowing the band gap energy from 3.7 eV for pure CeO2 to 3.1 eV for 20% Cu doped sample. The green PL emission band at ~520 nm (2.39 eV) is attributed to electronic decay from conduction band (CB) to donor band of oxygen vacancy (Ov), while the blue band at ~ 420 nm (2.9 eV) is due to electronic transition from CB to accepter band formed by ceria vacancies (VCe2−). The values of chromaticity coordinates and illuminating engineering parameters such as color rendering index (CRI) and correlated color temperature (CCT) of the studied samples predict their possible use in white light-emitting diode (LED).

Study of luminescence properties of dysprosium-doped CaAl12 O19 phosphor for white light-emitting diodes.

Dy3+ -doped CaAl12 O19 phosphors were synthesized utilizing a combustion method. Crystal structure and morphological examinations were performed respectively using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques to identify the phase and morphology of the synthesized samples. Fourier transform infrared spectroscopy (FTIR) estimations were carried out using the KBr method. Photoluminescence properties (excitation and emission) were recorded at room temperature. CaAl12 O19 :Dy3+ phosphor showed two emission peaks respectively under a 350-nm excitation wavelength, centered at 477nm and 573nm. Dipole-dipole interaction via nonradiative energy shifting has been considered as the major cause of concentration quenching when Dy3+ concentration was more than 3mol%. The CIE chromaticity coordinates positioned at (0.3185, 0.3580) for the CaAl12 O19 :0.03Dy3+ phosphor had a correlated color temperature (CCT) of 6057K, which is situated in the cool white area. Existing results point out that the CaAl12 O19 :0.03Dy3+ phosphor could be a favorable candidate for use in white light-emitting diodes (WLEDs).

Tailoring Emission Characteristics: Narrow-Band Red Luminescence from SLA to CaBa[Li2Al6N8]:Eu2+

Narrow-band red-emitting luminescent CaBa[Li2Al6N8]:Eu2+ for potential application in illumination-grade white-light-emitting diodes (WLEDs) was synthesized by reaction of the metal hydrides and nitrides in molybdenum crucibles in a hot isostatic press. Upon irradiation with high-energy visible light (444 nm), the material exhibits intense red and infrared luminescence (emission maxima, 636–639 nm, 790 nm; full width at half-maximum (fwhm), 1095–1266 cm–1 (48–57 nm), ≈1450 cm–1 (89 nm)). The red emission from Eu occupying the Ba site is nearly optimal for use in WLEDs combining outstanding color rendition and excellent luminous efficacy and the most narrow-band Eu2+ emission observed to date. The infrared emission intensity from Eu occupying the Ca site can be limited by reducing the activator concentration (here, 0.02–5 atom % Eu). CaBa[Li2Al6N8]:Eu2+ crystallizes isotypically with RbNaLi6Si2O8 in the monoclinic space group C2/m (no. 12) with unit cell parameters a = 16.0851(2), b = 6.467 38(4), c = 8.04...

All-Inorganic Perovskite Nanocrystals with a Stellar Set of Stabilities and Their Use in White Light-Emitting Diodes.

We report a simple, robust, and inexpensive strategy to enable all-inorganic CsPbX3 perovskite nanocrystals (NCs) with a set of markedly improved stabilities, that is, water stability, compositional stability, phase stability, and phase segregation stability via impregnating them in solid organic salt matrices (i.e., metal stearate; MSt). In addition to acting as matrices, MSt also functions as the ligand bound to the surface of CsPbX3 NCs, thereby eliminating the potential damage of NCs commonly encountered during purification as in copious past work. Quite intriguingly, the resulting CsPbX3-MSt nanocomposites display an outstanding suite of stabilities. First, they retain high emission in the presence of water because of the insolubility of MSt in water, signifying their excellent water stability. Second, anion exchange between CsPbBr3-MSt and CsPbI3-MSt nanocomposites is greatly suppressed. This can be ascribed to the efficient coating of MSt, thus effectively isolating the contact between CsPbBr3 and CsPbI3 NCs, reflecting notable compositional stability. Third, remarkably, after being impregnated by MSt, the resulting CsPbI3-MSt nanocomposites sustain the cubic phase of CsPbI3 and high emission, manifesting the strikingly improved phase stability. Finally, phase segregation of CsPbBr1.5I1.5 NCs is arrested via the MSt encapsulation (i.e., no formation of the respective CsPbBr3 and CsPbI3), thus rendering pure and stable photoluminescence (i.e., demonstration of phase segregation stability). Notably, when assembled into typical white light-emitting diode architecture, CsPbBr1.5I1.5-MSt nanocomposites exhibit appealing performance, including a high color rendering index ( Ra) and a low color temperature ( Tc). As such, the judicious encapsulation of perovskite NCs into organic salts represents a facile and robust strategy for creating high-quality solid-state luminophores for use in optoelectronic devices.

Preparation of Y3Al5O12:Ce nanophosphors using salt microemulsion method and their luminescent properties

Nano-yttrium aluminum garnet (YAG) is a promising material for use in white light-emitting diodes and biological fluorescent probe. However, its existing preparation methods often suffer from low synthesis temperature and particle agglomeration. Therefore, preparing YAG nanoparticles with both high crystallinity and high dispersibility is difficult, which severely limits the applications of nano-YAG phosphor. This work presents a salt microemulsion method that can yield YAG nanoparticles of size 4–6 nm that are dispersed at a high temperature (1000 °C). Transmission electron microscope analysis shows that the precursor particles are dispersed and isolated by nano-sized potassium sulfate particles. Because the melting point of potassium sulfate is high (1067 °C), the precursors and the YAG nanoparticles are always dispersed and isolated by the solid potassium sulfate salt during calcination at high temperatures, resulting in the formation of dispersed YAG nanoparticles with good crystallinity. The reflection spectrum of nano-YAG exhibited a redshift compared to that of bulk YAG. When the Ce content is 0.06, the nano-YAG phosphor exhibited the highest internal photoluminescence quantum yield of 51.2%, and the decrease in the particle size did not increase the quenching concentration. The nano-YAG prepared at a high temperature also exhibited improved optical stability: The luminescence intensity of the nano-YAG decreased by only~ 16% after 48 h of irradiation using blue laser. The obtained 4–6-nm-sized Y3Al5O12:Ce nanophosphors are expected to be ideal materials for novel fluorescent probes and preparation of transparent ceramics.

Highly thermally stable single-component warm-white-emitting ZANP glass: Synthesis, luminescence, energy transfer, and color tunability

Luminescent glass demonstrates potential for applications as color converters in white-light-emitting diodes (W-LEDs). In this study, solution combustion synthesis combined with low-temperature melt quenching was employed as a novel route for preparing new white-light fluorescent glasses (rare-earth-doped ZnO–Al2O3–Na2O–P2O5, ZANP). The developed solution combustion synthesis can considerably decrease the reaction temperature and time, with several advantages such as energy and time savings. X-ray diffraction and photoluminescence spectroscopy, as well as decay curves, CRI, and CCT, as well as the Commission Internationale de I′Eclairage (CIE) 1931 chromaticity coordinates, were assessed to examine the microstructure and photoluminescence properties of Tm3+/Dy3+ co-doped and Tm3+/Dy3+/Eu3+ tri-doped ZANP glasses for use in W-LEDs. Experimental results revealed that ZANP glass co-doped with Tm3+ and Dy3+ exhibits blue- and yellow-light emissions based on the energy transfer of dipole-dipole interaction between Tm3+ and Dy3+, which can realize the adjustment of color in a wide range. The emitting color coordinate (0.343, 0.344) of ZANP: 1.0Tm3+, 0.75Dy3+ approach ideal white light. Also, by the introduction of additional Eu3+ doping, ZANP:1.0Tm3+, 0.75Dy3+, 0.1%Eu3+ glass emit warm-white light (CCT = 3198 K) under an excitation of 361 nm. Moreover, the tri-doped ZANP glasses exhibit good thermal stability, where the luminous intensity at 498 K remains exceeding 50% of that at room temperature, and the color coordinate offset is only 2.87 × 10−2 relative to room temperature.

Synthesis and Luminescence Properties of Orange-Red Phosphors Na Y (WO4)2: Eu3+, Sm3+

Orange-red phosphors NaY(WO4)2:Eu3+, Sm3+ were successfully synthesised by hydrothermal synthesis method. The photoluminescence (PL) properties were investigated. The PL emission spectrum of Na Y (WO4)2: Eu3+ shows good luminous properties under 398 nm, which mainly located at 596 and 615 nm, with the additional of Sm3+ could broaden and increase emission intensity of Eu3+, which could be suitable for the excitation of UV light emitting diodes (LEDs) (∼400 nm). The PL results indicated that Na Y (WO4)2: Eu3+, Sm3+ may be a promising red phosphor candidate for use in white LEDs.

Facile fabrication and luminescence characteristics of Ce:YAG phosphor glass thick films coated on a glass substrate for white LEDs

A pivotal step in providing a better fluorescent material that has high luminous efficacy and excellent thermal stability is to utilize inexpensive phosphors for white light-emitting diodes (W-LEDs). Herein, we demonstrate a feasible tape-casting technique for creating phosphor thick films that consist of Ce: YAG phosphor embedded in relatively low melting point glass frits on an ultrathin glass substrate with controllable film thickness. The glass matrix has ideal densification and interfaces with the glass substrate at a relatively low temperature of 580°C. Subsequently, the structure and optical properties of the phosphor layer are investigated. In addition, the effect of the phosphor concentration, thick film thickness and location (top or bottom) of the phosphor layer on the photoluminescence properties and chromaticity are also discussed with respect to use in W-LEDs. Significantly, this promising structure has excellent thermal stability and the potential to overcome current limitations of phosphors in high-power W-LEDs. Finally, a high-performance W-LED based on the planar phosphor glass exhibits a luminous efficiency of 108.45lmW−1, a correlated color temperature of 5408K and a color rendering index of 76.

Pr3+/Ho3+ co-doped glass phosphors for application in warm white light-emitting diodes

Pr3+/Ho3+ co-doped fluorozirconate glasses were prepared and their luminescence properties studied. Blue, green and red luminescence in the wavelength region of 470–750nm were achieved in these glasses under 443nm light-emitting diode (LED) excitation. The ratio of Pr3+–Ho3+ was changed in order to determine the appropriate combination for realizing color-controlled white LEDs. The color temperature of the white light can be adjusted by changing the LED-excitation wavelength or the ratio of the Ho3+/Pr3+ ions. Thus, Pr3+/Ho3+co-doped fluorozirconate glasses are potential materials for use in white LEDs.

Multi-functionality of luminescent glasses for energy applications

Rare-earth-(RE) doped barium borate glasses are investigated for their potential use as photon downshifting cover glasses for CdTe solar cells and as converters for white light-emitting diodes (LEDs). The glasses are doped with trivalent RE ions such as Eu3+ and Tb3+, resulting in an intense luminescence in the red (Eu3+) and green (Tb3+) spectral range upon excitation in the ultraviolet and blue ranges. Doping the glasses with two different RE ions enables broader absorption, which is necessary for both photovoltaic applications and for the appropriate color mixing needed for use in white LEDs. Though the single-doped cover glasses already reveal a slight increase in the short-circuit current density of CdTe solar cells, the double-doped glasses allow for even higher efficiency gains due to the significantly broader spectral range for absorption. For an Eu3+/Tb3+ double-doped glass with an RE doping level of 1 at.% each, an efficiency increase of 1.32% can be achieved. Furthermore, the Eu3+/Tb3+ double-doped glasses enable appropriate color mixing in the green-to-red spectral range by varying the RE doping level accordingly.