White Lighting Devices Research Articles

White Light Realization and Color Coordinate Calculation of OLED Devices

White-light OLED devices can be used as a surface light source and for full color displays,which have become the focus of OLED research and development.However,there are some shortcomings in the realization of white-light OLED devices,such as insufficient luminous performance,difficult process control,and easy color drift.To solve these problems,the optimized ratios of primary colors(red,green,and blue)of organic OLED devices were preliminarily obtained through the realization of white light and calculation of the color coordinate.An experimental white-light OLED device was prepared with a color coordinate of(0.31,0.35).Further,theoretical calculations and experimental optimizations were carried out to reduce the red-light doping concentration and increase the green-light doping ratio to realize standard white-light(0.33,0.33)OLED devices.

Performance comparison of CuPc and 2T-NATA in organic light-emitting devices

Using CuPc as the hole buffer material, the effect of 2T-NATA and CuPc as hole buffer materials in similar structure on the performance of devices is studied. For this reason, the ITO/CuPc (20 nm)/NPBX/DPVBi (20 nm) (15 nm)/Alq3: Rubrene (10, X nm)/Alq3 (40 nm)/LIF/Al (5 nm) light-emitting device is designed. Referring to the previous papers on similar structure devices, the best effect is that the thickness of doped rubrene is 20 nm. In this paper, the thickness of Alq3 doping is 10 nm, the thickness of rubrene is adjusted to 5 nm, 10 nm, 15 nm, 20 nm and 25 nm, and the buffer thickness of CuPc is selected at 20 nm according to the previous experimental results. The experimental results show that when the thickness of rubrene is 20 nm, the yellow light and blue light of the light-emitting materials tend to balance, and the device is close to the white light device. The brightness and efficiency of the device are the highest, reaching and 21050 cd/m2 5.527 cd/A respectively. Compared with 2T-NATA as the buffer material, its luminous efficiency and brightness are improved. Through the analysis of the experimental results, we find that CuPc as a hole buffer material reduces the hole carrier injection barrier, improves the hole injection ability, and enhances the recombination probability of hole and electron, improves the luminous efficiency and brightness of the device. It is concluded that 2T-NATA is more suitable than CuPc in the aspect of practical application and energy saving. The advantage of CuPc is that it can inhibit the diffusion of chemical components in ITO to the hole transport layer, which is beneficial to the improvement on device performance and life.

Up‐conversion phosphor plate for white lighting device using NIR excitation source

AbstractUpconversion phosphors have numerous advantages compared to down conversion phosphor materials, such as a weak background interface, low excitation energy, sharp emission lines, and long lifetimes. Conventionally, blue laser diodes are used to obtain strong white light by combining green‐ and red‐emitting phosphors. The blue‐excited white‐light‐emitting devices can be harmful when the blue light penetrates directly into the human body. However, lower energy excited lighting devices does not harm the human body because of their low‐energy photons are compatible with the biologically safe window. Hence, we present a prototype device that converts invisible near‐infrared light into visible white light. For this, we synthesized orange‐emitting Y2O3:Er3+, Yb3+ and blue‐emitting Y2O3:Tm3+, Yb3+ upconversion phosphors using a solid‐state reaction. Using these, phosphor‐in‐glass (PiG) samples with sintered glass frit were prepared to investigate their optical behavior under low‐excitation energy. The emission color from the stacked PiGs depends on the color balance between the activator ions of Er3+, Tm3+, and Yb3+, and their balance is optimized to obtain a white light. The results might pave the way for designing safe white‐light‐emitting devices using a low‐energy excitation source.

Combination of broad emission bands of Ti3+,4+/ Eu2+,3+ co-doped OH− free low silica calcium aluminosilicate glasses as emitting phosphors for white lighting devices

In this report, Ti3+, 4+/Eu2+, 3+ co-doped OH− free low silica calcium aluminosilicate glasses (LSCAS) were synthesized and their optical properties investigated aiming applications as phosphors for white light generation. This research explores the possibility of combining the broad emission bands in the visible of these glasses co-doped with Ti3+,4+/Eu2+ ions with those in the red emitted by Eu3+, in addition to the high luminescence quantum yield they present. The excitation and emission results show that exciting the samples at 300 nm, a broad emission band is generated, embracing very well the visible region. The emission spectra were analyzed by (x-y) CIE-1931 chromaticity diagram and the color rendering index (CRI) presented Ra values up to 80, with the correlate color temperature (CCT) varying from 4995 to 6609 K. The luminescence quantum yield determined by Thermal Lens Spectroscopy showed values of 38 and 42% for the samples with (in wt%) 0.1Eu2O3-2.0TiO2 and 0.5Eu2O3-2.0TiO2, respectively. Finally, the energy transfer processes between these luminescent ions were discussed, highlighting the potential of the Eu–Ti LSCAS glasses as candidates for the development of devices for white light generation.

阴极耦合层对顶发射白光OLED器件光电性能影响

In order to analyze the effect of different thickness of C60 on optical and electrical properties of top-emitting OLED, in experiment, the transmittance of ETL/EIL/Mg:Ag/matching layers were numerically calculated and two top OLED with common cathode configurations were fabricated. The optical and electrical properties of OLED devices prepared with different thickness of C60 refractive index matching layers were analyzed. The results showed, the complex films with different C60 thickness have different transmittance, the complex films have high transmittance in wide range of wavelengths when C60 film thickness is 30~40 nm, the CIEx and CIEy values of transmittance spectra are extremely near to the equal energy (0.33, 0.33). In addition, it can be found that the electroluminescence spectra and the chromaticity coordinates of OLED devices are also heavily related to the thickness of C60 refractive index matching layers, which is consistent with the numerical results of transmission spectrum of multilayer (ETL/EIL/Mg:Ag/C60) at different thickness of C60 thin films and indicate that the luminous brightness and the color coordinates of top-emitting white light devices can be adjusted by different thickness of C60 refractive index matching layer to achieve white light emission close to equal energy.

Eu2+,3+/Pr3+ co-doped calcium aluminosilicate glass for tunable white lighting devices

At the present time there is no doubt that almost every country is experiencing a revolutionary change in the used devices for artificial lighting whether for public, for domestic or for work place illumination. This movement is taking place towards the substitution of fluorescent lamps to LED-phosphor based devices under the justification of reduction in energy consumption and mitigation of the contamination of environment produced by the mercury of fluorescent lamps. In this aspect, despite of the great effort of worldwide scientists to obtain a white lighting source with the emitting spectrum similar to that of the sunlight, it is recognized that there is still a challenge to be faced of getting luminescent materials with broad band excitation in the UV–Vis regions and large emission in the visible in order to allow tunable white lighting generation. Motivated by this interest, in this paper, Eu2+,3+/Pr3+ co-doped calcium aluminosilicate glasses were synthesized and spectroscopically investigated aiming at the development of smart white lighting devices. A prototype was developed to study the sample with excitation at 445 nm light emission diode (LED). The results indicate high color rendering index (CRI Ra ∼92–95) and tunable correlated color temperature (CCT from 5700 to 6600 K), covering the whole spectral daylight range. By using a second 405 nm LED together with the 445 nm one, the calculated Du’v’ values are suitable for indoor illumination. In this configuration, by adjusting the LEDs intensities it is possible to tune the CCT close to the white lighting region with CRI Ra nearly 95. These characteristics demonstrate that the Eu2+,3+/Pr3+ co-doped OH− calcium aluminosilicate glass is a strong candidate for smart white lighting with LEDs.

Study of the white organic electroluminescent devices performance based on phosphorescent dyes FCNIrPic

Two kinds of high efficient white-light OLED devices based on blue phosphorescent material FCNIrPic(Bis(3,5-difluoro-4-cyano-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium(III))) were fabricated by means of the principle of whitening with blue-yellow complementary colors. Firstly, white-light device A was fabricated by the hybrid of yellow fluorescent material Rubrene and blue-light layer of phosphorescent FCNIrPic. The device structure is ITO/m-MTDATA/NPB/Rub/MCP: FCNIrPiC/Alq3/LiF/Al. The structure of the device is optimized by adjusting the thickness of phosphorescent doping layer MCP: FCNIrPiC. When the thickness of blue layer is 8 nm, the device has the best performance. The maximum brightness is 13240 cd/m2 and the maximum current efficiency is 3.5 cd/A. The color coordinates are near (0.33, 0.37) and change little with the increase in voltage. Secondly, white OLED device B with double phosphorescent layer was fabricated by yellow phosphorescent PO-01 and FCNIrpic. The device structure is ITO/m-MTDATA/NPB/CBP: PO-01/MCP: FCNIrpic/Alq3/LiF/Al. White light was obtained by adjusting the thickness of blue layer. When the thickness of blue layer is 10 nm, the device has the best performance. The maximum current efficiency is 9.8 cd/A and the maximum brightness is 11 400 cd/m2. The color coordinates are near (0.33, 0.35).

Tuning visible-wavelength spectrum of white-light super-continuum via etalon transmission in lamellar ZnO micro/nanoparticle-stacked structures

Multi-layered micro/nanostructures enable the fine-tuning of spectral bandwidth induced by coherent interference of multi-scattering and refraction bounded by a motive of Fabry Perot etalon. In this paper a ZnO micro/nanostructured thin film device is grown on a 21 nm silver film-sputtered sapphire substrates (0001) and attempted to be complied as a transmission-mode white-light spectrum tuning device. In details, the growth of the structures as a function of temporal duration and the effects of deposition of a 21 nm silver film atop sapphire substrates to the structural and optical properties of ZnO structures are investigated. Results of SEM imaging reveals that the insertion of the silver film enables synthesis of round ZnO particles at micro or nanoscales depending on the duration of growth time as opposed to the floral pattern associated with plain sapphire substrates. Characterizing material crystallization by XRD spectra found one dominant and two minor peaks along the planes of crystallization (002), and (100) and (101), correspondingly. Also, the characteristic PL peak at 380 nm was confirmed when excited at 325 nm, and the intensity decreases as the duration of growth time increases. Finally, growth duration-dependent modulation of peak wavelength and spectral bandwidth of the continuum laser was demonstrated.

One-step Hydrothermal Synthesis of Copper Doped Carbon Dots and Their Application in White Light Devices†

One-step Hydrothermal Synthesis of Copper Doped Carbon Dots and Their Application in White Light Devices†

Configuration- and concentration-dependent hybrid white light generation using red, green, and blue quantum dots embedded in DNA thin films.

Artificial white-light production from primary red, green, and blue (RGB) colours is in high demand in the lighting, information technology, and wearable display industries, and it requires a simple device structure and efficient templates with stable luminophores. To realize efficient and stable optoelectronic devices, relevant materials and device structures need to be identified. Therefore, we report the construction of a simple hybrid white-light optoelectronic device with a single excitation source with efficient RGB colours on a stable optical platform. Emission wavelength-tunable R, G, and B quantum dots (QDs) with specific ligands and cetyltrimethylammonium chloride (CTMA)-modified DNA (CDNA) are prepared for the fabrication of QDs embedded in CDNA thin films with mixed and orthogonally stacked configurations. Fourier transform infrared, photoluminescence quantum yield (PLQY), ultraviolet (UV)-vis absorbance, photoluminescence, and electroluminescence (excited by blue and UV LEDs) spectra of the QDs embedded in CDNA thin films are analyzed to investigate their ligand attachment, luminescence efficiency, optical excitation, spectral emission, and hybrid white-light properties. In addition, the dispersion and photostability of QDs in the CDNA matrix were analyzed. The colour rendering index (CRI) values and colour gamut of the QDs embedded in CDNA thin films are studied for evaluating the light quality. The results show that the ligands on the QDs enhance PLQY up to 95 and 25% in liquid and solid phases, respectively. The optical properties of the QDs in the CDNA thin films are not significantly affected by phase changes, which implies the effective hosting of QDs within CDNA. The CRI values of the mixed and stacked configuration-dependent QDs embedded in CDNA thin films are 21 and 80%, respectively, which suggest the relatively stronger self-absorption of R QDs in the mixed configuration than in the stacked configuration. In addition, CRI values and colour gamut are affected by different R, G, and B QD concentrations in CDNA. These findings are important for solid-state lighting, information display systems, flexible displays, and wearable displays.

Transparent Ce:GdYAG ceramic color converters for high-brightness white LEDs and LDs

Transparent Ce:GdYAG ceramic phosphors with different Gd3+ contents were successfully prepared by the solid-state reaction method. The absorption and emission properties were investigated at different temperatures. The highest luminous efficiency of 123.7 lm/W was obtained by Ce:YAG ceramic phosphor with the thickness of 1 mm. The addition of Gd3+ results in red-shift and broadening of the emission band of Ce3+ so that the color rendering index (CRI) increases and the correlated color temperature (CCT) decreases obviously after packaged with blue light-emitting diode (LED). The color coordinates of the Ce:GdYAG ceramic phosphor with 50% Gd3+ content based white light device are located at the theoretical white light point in the CIE-1931 chromaticity diagram. And the various CRI and adjustable CCT of warm white light emitted by this device and the high luminous efficiency make Ce:GdYAG ceramics the most promising candidate for high-brightness white LEDs and laser diodes(LDs) device.

Optimization for white organic light-emitting diode based on DCJTB as color conversion layer

In this paper, combining phosphorescence and fluorescence to form white light was realized based on DCJTB:PMMA/ITO/NPB/TCTA/FIrpic:TCTA/TPBi/Ir(ppy)3:TPBi/TPBi/Cs2CO3/Al. The effects of red fluorescence on this white light device was studied by adjusting the concentration of DCJTB. The study shows that the device with a DCJTB concentration of 0.7% in the color conversion layer (CCL) generates a peak current efficiency and power efficiency of 23.4 cd ⋅ A[Formula: see text] and 7.5 lm ⋅ W[Formula: see text], respectively. And it is closest to the equal-energy white point of (0.33, 0.33) which shows a CIE (Commission Internationale de L’Eclairage) coordinate of (0.35, 0.43) and a color rendering index (CRI) of 70 at current density of 10 mA ⋅ cm[Formula: see text]. In order to improve the efficiency, we design and fabricate both high efficient and pure white organic light-emitting diode (WOLED) by replacing the single blue emission layer (EML) with double EMLs of FIrpic:TCTA and FIrpic:TPBi. The further study shows that, when the layers of EML is three and the concentration of DCJTB at 0.7%, the device exhibits good performance specifically, at current density of 10 mA ⋅ cm[Formula: see text], the current efficiency of 28.2 cd ⋅ A[Formula: see text] (power efficiency of 10.3 lm ⋅ W[Formula: see text]), and the CIE coordinate of (0.33, 0.31) (CRI of 80.38).

Tuning white upconversion emission in GdPO4:Er/Yb/Tm phosphors

Nanoscale phosphors of Yb3+/Er3+/Tm3+-doped GdPO4 with different morphologies were synthesized using the solvothermal method with annealing at 750 °C and 1000 °C. A high concentration of Yb3+(35%mol) ions was successfully doped in the powders. Crystal structures were characterized through powder XRD measurement and Fourier transform infrared spectroscopy. SEM images have shown that the morphologies of the samples can be controlled by adjusting the pH value during their synthesis. Upconversion luminescence was investigated under 980 nm diode laser excitation. The upconversion processes were assessed on the basis of the power dependence of upconversion emission intensity. The light colour was investigated with respect to the 1931 CIE diagram. The samples show good emission tunability by monitoring the annealing temperature and the diode laser pump intensity. By properly adjusting the excitation power, white upconversion luminescence can be attained. Yb3+/Er3+/Tm3+-doped GdPO4 nanophosphors appear, which have potential applications in the field of upconversion-based white lighting devices.

Impact of crystal defect on upconverted white-light emission in lanthanide-doped LiNbO3 single crystal

Efficient and stable upconversion white-light is critical for optical applications. Herein, LiNbO3:Ho/Yb/Tm single crystals with different [Li]/[Nb] ratios were grown by Czochralski method. It is found that the crystal structures are not changed with [Li]/[Nb] ratios which varied from 0.946 to 0.991 in the single crystals. The RE ion concentrations are reduced faintly and crystal structures approach perfect with increasing the [Li]/[Nb] ratios. More ideal upconversion white-light is obtained when the [Li]/[Nb] ratio is close to 1. The integrated effects of intrinsic defect concentrations and RE ion concentrations affect the upconversion emission intensity of the single crystal. The lower crystal defect in the bulk single crystal has a positive impact on the enhancement of upconversion emission intensity. In addition, all the CIE coordinates are hardly changed with [Li]/[Nb] ratios and located in the white-light region. The upconversion mechanism analysis indicates the longer lifetimes of intermediate energy levels and the shorter lifetimes of luminous energy levels are beneficial to the upconversion process, and the larger intensity variation of upconversion emission arises from its greater lifetime variations of energy levels. The near-stoichiometric LiNbO3:Ho/Yb/Tm single crystal demonstrates potential applications in stable white-light devices and photoelectric instruments.

Enhanced photoluminescence properties of electrospun Dy3+ -doped ZnO nanofibres for white lighting devices.

Dy3+ -doped ZnO nanofibres with diameters from 200 to 500nm were made using an electrospinning technique. The as-fabricated amorphous nanofibres resulted in good crystalline continuous nanofibres through calcination. Dy3+ -doped ZnO nanofibres were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) light spectroscopy, Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL). XRD showed the well defined peaks of ZnO. UV-vis spectra showed a good absorption band at 360nm. FTIR spectra showed a Zn-O stretching vibration confirming the presence of ZnO. Photoluminescence spectra of Dy3+ -doped ZnO nanofibres showed an emission peak in the visible region that was free from any ZnO defect emission. Emissions at 480nm and 575nm in the Dy3+ -doped ZnO nanofibres were the characteristic peaks of dopant Dy3+ and implied efficient energy transfer from host to dopant. Luminescence intensity was found to be increased with increasing doping concentration and reduction in nanofibre diameter. Colour coordinates were calculated from photometric characterizations, which resembled the properties for warm white lighting devices.

Synthesis of widely emission-tunable Ag–Ga–S and its quaternary derivative quantum dots

Chalcopyrite I – III–VI chalcogenides have attracted great attention as environmentally benign, non-Cd compositions for synthesis of colloidal quantum dot (QD) emitters. Various Cu-based I–III–VI compositions have been intensively investigated for synthesis of highly fluorescent QDs, while the compositional diversity of Ag-based QD emitters remains still limited. Here, we explore synthesis of Ag-based I–III–VI QDs of ternary Ag–Ga–S (AGS) and its derivative quaternary Zn–Ag–Ga–S (ZAGS) and Ag–In–Ga–S (AIGS) QDs through alloying AGS with Zn2+ and In3+ ions, respectively. Being in line with the variation of band gap of a series of these QDs, they exhibit a systematic, wide photoluminescence (PL) tunability from blue (450 nm, the shortest PL wavelength reported to date from I–III–VI QD emitters) from the highest-band gap ZAGS to amber color (570 nm) from the lowest-band gap AIGS with high PL quantum yields of 58–69% after elaborate ZnS shelling. Among QDs above, two AIGS/ZnS QDs with different In contents, which are capable of efficiently absorbing blue photons, are further applied as down-converters in combination with a blue light-emitting diode (LED) to produce bicolored white solid-state lighting devices and down-conversion emission properties of the resulting white QD-LEDs are described in detail.

White perovskite based lighting devices.

Hybrid organic-inorganic and all-inorganic metal halide perovskites have been one of the most intensively studied materials during the last few years. In particular, research focusing on understanding how to tune the photoluminescence features and to apply perovskites to optoelectronic applications has led to a myriad of new materials featuring high photoluminescence quantum yields covering the whole visible range, as well as devices with remarkable performances. Having already established their successful incorporation in highly efficient solar cells, the next step is to tackle the challenges in solid-state lighting (SSL) devices. Here, the most prominent is the preparation of white-emitting devices. Herein, we have provided a comprehensive view of the route towards perovskite white lighting devices, including thin film light-emitting diodes (PeLEDs) and hybrid LEDs (HLEDs), using perovskite based color down-converting coatings. While synthesis and photoluminescence features are briefly discussed, we focus on highlighting the major achievements and limitations in white devices. Overall, we expect that this review will provide the reader a general overview of the current state of perovskite white SSL, paving the way towards new breakthroughs in the near future.

Optical Properties and Reliability Studies of Gradient Alloyed Green Emitting (CdSe)x(ZnS)1–x and Red Emitting (CuInS2)x(ZnS)1–x Quantum Dots for White Light-Emitting Diodes

Luminescent materials become one of interesting issues for white LED-based lighting devices (WLEDs) due to their high performances for converting the monochromatic light from UV/blue LED chips into white light. Nevertheless, the availability of rare earth materials, the low color rendering index (CRI) and too-cold color temperature of the white LEDs remain some drawbacks to penetrate into the general LED lighting markets. Herein, we report the development of rare-earth-free luminescent nanocomposites combined with a UV/blue LED chip in order to provide white light. Gradient alloyed cadmium selenide/zinc sulfide (CdSe)x(ZnS)1–x and copper indium sulfide/zinc sulfide (CuInS2)x(ZnS)1–x quantum dots have been used to achieve the luminescent nanocomposite films in silicone as polymer matrix. The optical performances were investigated upon LED excitation. The photometric parameters of systems consisting of luminescent nanocomposites and LEDs including color rendering index (CRI), correlated color temperature (C...

Enhanced and Stable Upconverted White-light Emission in Ho3+/Yb3+/Tm3+-doped LiNbO3 Single Crystal via Mg2+ Ion Doping

A strategy to enhance the upconversion white-light intensity via Mg2+ ion doping was demonstrated in Ho3+/Yb3+/Tm3+/LiNbO3 single crystal. It is found Mg2+ ion doping affects the crystal field symmetry around RE3+ ions and enhance the upconversion emission intensity. Bright white-light is obtained when the Mg2+ ion concentration is 0.5 mol% in the melt. And the CIE coordinates are hardly changed with Mg2+ ion doping. In addition, the upconversion mechanism is discussed in detail. It is observed the longer lifetimes of intermediate levels result in the lower upconversion photon numbers, which are beneficial to the upconversion process. Therefore, Mg2+ ion doped Ho3+/Yb3+/Tm3+/LiNbO3 single crystals would have potential applications in stable white-light devices and photoelectric instruments.

(Invited) All-Inorganic YAG Phosphor-in-Glass Light Convertor for Next-Generation Modular High-Brightness White LEDs/Lds

Super-high brightness, reliability, and modularization are three key features of state-of-the-art high-brightness solid state lighting, such as high-power white light-emitting diodes (white LEDs) and white laser diodes (white LDs). However, these features are inevitably limited by the organic resin packing material, as a crucial component of the white lighting device, because of its unstable property at high temperature and low thermal conductivity. Here, we report a robust light convertor that can simultaneously play key roles as a phosphor and an alternative encapsulating material via phosphor-in-glass (PiG) engineering. We employed a combination of powder X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), EDS mapping, confocal laser scanning microscope (CLSM), cathodoluminescence (CL) mapping, in conjunction with micro-PL system with a point-by-point scanning mode to study the detailed structure of PiG samples. This Y3Al5O12:Ce3+-based PiG exhibits a high external quantum efficiency of ~60%, a high thermal conductivity of ~0.59 W/mK, exceptional thermal stability, and excellent moisture resistance. By combining the as-synthesized PiG with high-power blue chip-on-board (COB), a high luminous efficacy (92 lm/W) modular white LEDs with a luminous flux up to 1076 lm and a high color rendering modular warm white LEDs (Ra = 90.3 and CCT = 3585 K) are achieved. Moreover, a modular white LDs with a higher luminous efficacy (110 lm/W) is also achieved through blue LDs pumping. The results demonstrate that this easy-fabrication, low-cost, and long-term reliable high-brightness modular white LEDs or white LDs is expected to be a promising candidate for next-generation illumination.