Solid-state Light Sources Research Articles

Development of Trivalent Samarium Ion-Doped Barium Fluoroborotellurite Glasses for Solid-State Lighting and Scintillation Material

In this research we developed Sm3+ ion-doped fluoroborotellurite with formula 30B2O3-(30-x)TeO2-10ZnF2-30BaO-xSm2O3 where x = 0.0; 0.05; 0.1; 0.5; 1.0; and 1.5 mol%. They developed using the melt-quenching technique. The raw material is melted at 1150°C for 1 hour 30 minutes and annealed at 500°C for 1 hour 30 minutes. The optimum concentration was found at 1.0 mol% of Sm3+ ion in the glass system. Their physical, optical, photoluminescence properties and lifetime were observed. The absorption spectra show strong absorption peaks at 1232 nm due to 6H5/2→6F7/2 transition. The photoluminescence properties show a strong emission at 600 nm under λex=403 nm because of 4G5/2→6H7/2 transition. The CIE 1931 coordinate confirms the orange emission color with 81% efficiency (η). From all results, we can summarize that our glass sample can be developed as a solid-state lighting source in the orange region.

Phantom array and stroboscopic effect visibility under combinations of TLM parameters

Solid-state light sources can be more prone to larger temporal light modulation (TLM) than conventional sources. TLM visibility depends on wave shape, frequency, modulation depth and duty cycle, and is affected by the sensitivity of the observer. TLM can be visible well above the critical flicker fusion frequency, when there is relative movement between the observer’s eyes and light source, lighted space or moving objects in the field of view. This human subjects experiment explored visibility of the stroboscopic effect (SE) versus the phantom array effect (PAE) with targeted tasks under 74 TLM waveforms. The results showed the SE visibility peaks between 90 Hz and 120 Hz, while the PAE visibility peaks between 500 Hz and 1000 Hz. The phantom array is visible to sensitive participants at 6000 Hz. Both effects are more visible under rectangular versus sinusoidal TLM, higher modulation, and when duty cycles are 10% or 30% versus 50%. Higher sensitivity participants, differentiated using the Leiden Visual Sensitivity Scale, rated TLM waveforms as more visible, especially those inherently harder to see. This work lays a foundation for a PAE metric and guides driver and dimmer designers toward electronic circuits that minimize the visibility of TLM in LED products.

55‐3: Invited Paper: From Smallest AR Glasses to Mainstream Display Projection — Latest Advances of Visible LED and Laser Solutions

Solid state light sources for projection displays have shown tremendous progress over the recent years. Their application usage is ranging from low luminance near to eye projection for augmented reality glasses to mainstream projectors. This presentation will share some of the latest progresses for laser and LEDs for Near‐to‐eye (NTE) displays and will describe important design challenges such as package integration and power efficiency. Besides, High Current LEDs are further pushing the limits and bring LED based projection light engines on eye‐to‐eye brightness level with lamp & laser‐based systems ranging up to 5,000 ANSI lumens.

Improved stability and luminescent efficiency of AgInSe2 nanocrystals by shelling with ZnS

In this paper, AgInSe2 (AISe) core and AgInSe2/ZnS (AISe/ZnS) core/shell nanocrystals (NCs) were synthesised by a one-pot method in an organic solvent. Firstly, the synthesis of AIS core NCs with different sizes was performed by hot-injection of Se precursor into the Ag and In complexes at different temperatures from 100 °C to 180 °C for a reaction time of 20 min Then, the ZnS was grown on the surface of AISe NCs at 150 °C for 60 min to produce the AISe/ZnS core/shell structures. The as-synthesised AISe core and AISe/ZnS core/shell NCs were characterised by using x-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and optical spectroscopies (UV–vis absorption and photoluminescence (PL)). After shelling ZnS layer, AISe/ZnS core/shell NCs become more stable (12 months) in ambient air and emit strong luminescence with a high quantum yield (QY) of 40% in the range from 610 nm to 762 nm by varying the reaction temperature of AISe core synthesis from 100 °C to 180 °C. The observed increase of QY and blue-shift in photoluminescence spectra after coating ZnS on surface AISe core NCs are rationalised by the formation of the alloyed structure and passivation of surface states. With their outstanding luminescent properties, AISe core and AISe/ZnS core/shell NCs are very promising in designing emitters for solid-state lighting sources in the greenhouse and in-door farming and bio-related devices.

A garnet Ca2GdZr2Ga3O12:Cr3+ phosphor with ultra-broadband near-infrared luminesce for night-vision and biomedical imaging

It is urgent and crucial to develop highly efficient broadband Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) which are applied in tiny solid-state NIR light sources. However, a lot of NIR phosphors suffer from low quantum yield and poor thermal stability in recent years. Hereon, the solid-state reaction synthesis process was used to create a new garnet Ca2GdZr2Ga3O12:Cr3+ (CGZG:Cr3+) phosphor, which can produce a broad range emission peak at (12,437 cm-1, 804 nm) with a full width at half maximum (FWHM) of (67567 cm−1, 148 nm). At 373 °C, thermal stability was determined to be 76%, an IQE of 75% and an EQE of 26% was observed. When driving current at 150 mA and 320 mA, the device achieved the output power of 473 mW and 968 mW. The results demonstrate CGZG:Cr3+ phosphor-convert NIR LEDs have great potential for applications in night-vision and biomedical imaging NIR spectroscopy technology.

Cost Estimates of Roll-to-Roll Production of Organic Light Emitting Devices for Lighting

White organic light emitting devices (WOLEDs) offer distinct advantages as solid state lighting sources, including high energy efficiency, superior color quality, and a flexible, thin profile that can accommodate a vast array of possible fixture designs. Recent advances in device lifetime and high speed deposition suggest that mass production of WOLED panels is approaching an inflection point. To understand the tradeoffs in the volume manufacturing of WOLED lighting panels, in this work, we estimate the cost of white WOLED panel production based on vacuum and vapor phase deposition in a roll-to-roll production line envisioned to yield an annual capacity of at least 6 × 106 m2. Assuming a WOLED operating luminance at 10 klm/m2, we anticipate a $12.5/klm cost of a WOLED light engine that includes the cost of the current driver and packaging. With incremental reduction in material and driver costs and improved luminance, the cost of WOLED lighting can be reduced to $6.3/klm in the near term, potentially positioning WOLEDs for use in numerous premium lighting applications.

Ce:LYSO, from scintillator to solid-state lighting as a blue luminescent concentrator

Cerium-doped lutetium-yttrium oxyorthosilicate (Ce:LYSO) is a well-known single crystal scintillator used in medical imaging and security scanners. Recent development of high power UV LED, matching its absorption band, questions the possibility to use Ce:LYSO in a new way: as LED-pumped solid-state light source. Since Ce:LYSO is available in large size crystals, we investigate its potential as a luminescent concentrator. This paper reports an extensive study of the performance in close relation to the spectroscopic properties of this crystal. It gives the reasons why the Ce:LYSO crystal tested in this study is less efficient than Ce:YAG for luminescent concentration: limited quantum efficiency and high losses coming from self-absorption and from excited-state absorption are playing key roles. However, we demonstrate that a Ce:LYSO luminescent concentrator is an innovative source for solid-state lighting. Pumped by a peak power of 3400 W in quasi-continuous wave regime (40 µs, 10 Hz), a rectangular (1 × 22 × 105 mm3) Ce:LYSO crystal delivers a broadband spectrum (60 nm FWHM) centered at 430 nm. At full output aperture (20 × 1 mm2), it emits a peak power of 116 W. On a squared output surface (1 × 1 mm2) it emits 16 W corresponding to a brightness of 509 W cm–2 sr–1. This combination of spectrum power and brightness is higher than blue LEDs and opens perspectives for Ce:LYSO in the field of illumination namely for imaging.

Generation of 13.9-mJ Terahertz Radiation from Lithium Niobate Materials.

Extremely strong-field terahertz (THz) radiation in free space has compelling applications in nonequilibrium condensed matter state regulation, all-optical THz electron acceleration and manipulation, THz biological effects, etc. However, these practical applications are constrained by the absence of high-intensity, high-efficiency, high-beam-quality, and stable solid-state THz light sources. Here, the generation of single-cycle 13.9-mJ extreme THz pulses from cryogenically cooled lithium niobate crystals and a 1.2% energy conversion efficiency from 800nm to THz are demonstrated experimentally using the tilted pulse-front technique driven by a home-built 30-fs, 1.2-Joule Ti:sapphire laser amplifier. The focused peak electric field strength is estimated to be 7.5MVcm-1 . A record of 1.1-mJ THz single-pulse energy at a 450 mJ pump at room temperature is produced and observed that the self-phase modulation of the optical pump can induce THz saturation behavior from the crystals in the substantially nonlinear pump regime. This study lays the foundation for the generation of sub-Joule THz radiation from lithium niobate crystals and will inspire more innovations in extreme THz science and applications.

Polarization study of single color centers in aluminum nitride

Color centers in wide-bandgap semiconductors are a promising class of solid-state quantum light source, many of which operate at room temperature. We examine a family of color centers in aluminum nitride, which emits close to 620 nm. We present a technique to rapidly map an ensemble of these single photon emitters, identifying all emitters, not just those with absorption dipole parallel to the laser polarization. We demonstrate a fast technique to determine their absorption polarization orientation in the c-plane, finding they are uniformly distributed in orientation, in contrast to many other emitters in crystalline materials.

Microwave-assisted synthesis and thermally stable red fluorescence of Ba3(ZnB5O10)PO4:Eu3+ solid solution

Red-emitting materials play a significant role in phosphor-converted white light-emitting diodes (WLEDs), since it can effectively improve the chromatic properties of the solid-state lighting source. In this work, we employ a microwave-assisted solid-state reaction to prepare a red-emitting Ba3(ZnB5O10)PO4:Eu3+ (BZBP:Eu3+) phosphor. Eu3+ activators are solidly dissolved into the BZBP host via occupying the Ba2+ positions. Excited by 395 ​nm, the title phosphor yields red emission with high color purity, which is dominated by the electric dipole transition of Eu3+. Base on the investigation of photoluminescence in response to the Eu3+ content, the content quenching mechanism is understood. Besides, the study on the luminescence temperature quenching reveals the good thermal stability and resistance to chromaticity shifting. The results indicate that the studied phosphor would be an alternative red-emitting material for WLEDs.

Solid-State Far-Ultraviolet C Light Sources for the Disinfection of Pathogenic Microorganisms Using Graphene Nanostructure Field Emitters.

The ongoing global outbreak of coronavirus disease has necessitated the use of ultraviolet (UV) disinfection techniques to reduce viral transmission in public places. The previously used UV wavelength is harmful to the human body,the wavelength range from 200 to 235nm, often referred to as far-UVC light, has attracted attention as a novel disinfection wavelength range that can be used in a safe manner. However, the currently used light sources have practical problems, such as an expensive cost, a low efficiency, and short lifetimes. Therefore, environmentally friendly solid-state light sources with a lower cost, higher efficiency, and longer lifetimes are demanded. Here, an efficient mercury-free far-UVC solid-state light source is presented. This light source demonstrates intense 230nm emission with a narrow spectral width of 30nm and a long lifetime of more than 1000 h. These characteristics can be achieved by graphene nanostructure field emitters and wide-bandgap magnesium aluminate phosphors. By using this light source, the efficient disinfection of Escherichia coli is demonstrated. The light sources presented here facilitate future technologies for preventing the spread of infectious diseases in a safe and convenient manner.

Quantum Cutting in KGd(CO3)2:Tb3+ Green Phosphor

Phosphors with a longer excitation wavelength exhibit higher energy conversion efficiency. Herein, quantum cutting KGd(CO3)2:Tb3+ phosphors excited by middle-wave ultraviolet were synthesized via a hydrothermal method. All the KGd(CO3)2:xTb3+ phosphors remain in monoclinic structures in a large Tb3+ doping range. In the KGd(CO3)2 host, 6D3/2 and 6I17/2 of Gd3+ were employed for quantum cutting in sensitizing levels. The excited state electrons could easily transfer from Gd3+ to Tb3+ with high efficiency. There are three efficient excited bands for quantum cutting. The excited wavelengths of 244, 273, and 283 nm correspond to the transition processes of 8S7/2→6D3/2 (Gd3+), 8S7/2→6I17/2 (Gd3+), and 7F6→5F4 (Tb3+), and the maximum quantum yields of KGd(CO3)2:Tb3+ can reach 163.5, 119, and 143%, respectively. The continuous and efficient excitation band of 273-283 nm can well match the commercial 275 nm LED chip to expand the usage of solid-state light sources. Meanwhile, the phosphor also shows good excitation efficiency at 365 nm in a high Tb3+ doping concentration. Therefore, KGd(CO3)2:Tb3+ is an efficient green-emitting phosphor for ultraviolet-excited solid-state light sources.

Visually Hidden, Self-Assembled Porous Polymers for Optical Physically Unclonable Functions

Owing to the advancement of security technologies, several encryption methods have been proposed. Despite such efforts, forging artifices is financially and somatically becoming a constraint for individuals and society (e.g., imprinting replicas of luxury goods or directly life-connected medicines). Physically unclonable functions (PUFs) are one of the promising solutions to address these personal and social issues. The unreplicability of PUFs is a crucial factor for high security levels. Here, this study proposes a visually hidden and self-assembled porous polymer (VSPP) as a tag for optical PUF systems. The VSPP has virtues in terms of wavelength dependency, lens-free compact PUF system, and simple/affordable fabrication processes (i.e., spin coating and annealing). The VSPP consists of an external saturated surface, which covers the inner structures, and an internally abundant porous layer, which triggers stochastic multiple Mie scattering with wavelength dependency. We theoretically and experimentally validate the unobservability of the VSPP and the uniqueness of optical responses by image sensors. Finally, we establish a wavelength-dependent PUF system by using the following three components: solid-state light sources, a VSPP tag, and an image sensor. The captured raw images by the sensor serve as "seed" for unique bit sequences. The robustness of our system is successfully confirmed in terms of bit uniformity (∼0.5), intra/interdevice Hamming distances (∼0.04/∼0.5), and randomness (using NIST test).

Multicolor-emission of Gd2O3:Bi3+ and its application for white light emitting diodes

White light-emitting diodes (W-LEDs) have been becoming the next generation of solid-state light sources. However, W-LED phosphors are dependent on rare earth doping. In this work, a Gd2O3:Bi3+ phosphor without rare earth doping to achieve multicolor luminescence was developed by a simple sol-gel method. Photoluminescence spectra were investigated for Gd2O3:Bi3+ at various annealing temperatures and various doping concentrations. The results show that Bi3+ doping does not cause the structural change of Gd2O3. The strongest emission peaks of the phosphor are located at 420 and 530 nm, corresponding to the 3P1→1S0 transition of Bi3+. The excited phosphors showed sharp blue emission peaks and broad yellow-green emission peaks, showing the overall characteristics of white emission. Under the excitation of UV chip, the LED device has excellent white-light emission performance. The non-toxic Bi3+ was used to realize W-LEDs devices, providing a new possibility for the development of LED as well as great practical significance in environmental protection.

A Review of Advances in Lighting Systems’ Technology—The Way Toward Lighting 4.0 Era

Research and development over the last century have historically concentrated on improving one specific aspect of energy efficiency. The market penetration rate for systems using solid-state light sources is currently between 40 and 45 percent, and it is rising. This paper provides an update on the state of lighting technology based on the compilation of more than 160 recent documents. The only widespread use of solid-state lighting sources over the next years might help reduce greenhouse gas emissions by up to 500 Mtn per year and decrease electrical energy utilization for illumination by up to 4% by 2030. But this forecast could be severely affected by the “rebound effect”. Switching to the SSL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> concept, which consists of Sustainable Smart Lighting (SSL) systems based on Solid State Lighting (SSL) devices, might be one way to stop that harmful effect. Smart, human-centered lighting that incorporates light quality is driven by “appliance efficiency”. This merely suggests that the "Right Light" should be provided by next-generation lighting systems with the best levels of quality and efficiency when and where it is needed.

Electronic structure study of dual-doped II-VI semiconductor quantum dots towards single-source white light emission.

Single-source white light emitting colloidal semiconductor quantum dots (QDs) is one of the most exciting and promising high-quality solid-state light sources to meet the current global demand for sustainable resources. While most of the previous methods involve dual (green-red) emissive nanostructures coated on blue LEDs to achieve white light, this work describes a single-source white light emitter of robust and superior quality using dual-doping. A modified synthesis method for intense white light emitting Cu, Mn dual-doped ZnSe QDs is engineered such that the extent of doping and concentration of ligands can alter their electronic structures. This is then customized to obtain various types of white light emissions ranging from warm white to cool white. Further, the composition-driven change in the electronic structure of the host QDs is exploited to achieve emission tunability over the entire visible range.

CMOS-compatible integration of telecom band InAs/InP quantum-dot single-photon sources on a Si chip using transfer printing

We report the hybrid integration of a telecom band InAs/InP quantum-dot (QD) single-photon source on a CMOS-processed Si photonics chip using transfer printing. The integration technique allows for the assembly of photonic components in a pick-and-place operation and therefore can introduce them on Si photonics chips after completing the entire CMOS-compatible fabrication processes. We demonstrate telecom single-photon generation from an InAs/InP QD integrated on Si and its coupling into a waveguide. We also demonstrate the integration of a QD on a fiber-pigtailed Si chip and single-photon output through the optical fiber, showing a novel pathway for modularizing solid-state quantum light sources.

White light-emitting properties and application testing of Eu3+ co-doped Gd5Si2BO13:Dy3+ phosphors with energy transfer between Dy3+ and Eu3+

LED occupies a broad market due to its many advantages as a fourth-generation solid-state light source. However, single-component white LED generally has the disadvantages of high coloring temperature, low thermal stability, and low luminous efficiency. In order to solve these problems, Gd5Si2BO13:Dy3+,Eu3+ was prepared by a high temperature solid state method using a newer borate matrix based on Gd5Si2BO13. A colour-tunable warm white phosphor was achieved by energy transfer between Dy3+ and Eu3+. The crystal structure, luminescence characteristics, thermal stability of luminescence, fluorescence lifetime and energy transfer mechanism were systematically studied, and the samples obtained had excellent luminescence performance. Its thermal stability of 150 °C luminescence was 83.77%. By adjusting the ratio of Eu3+, its color changes from cool white light to warm white light and finally moves to red light. Its corresponding color temperature can be adjusted to a range of 5475k∼2128 K. The packaging w-LED application test and the application test of colorless fluorescent anti-counterfeiting printing ink were carried out, and both showed excellent performance. This is the first time that Dy3+ and Eu3+ have been studied in Gd5Si2BO13, further understanding the newer substrate Gd5Si2BO13, and promoting the application of single-component warm white LED. Therefore, Gd5Si2BO13:Dy3+,Eu3+ have good market application prospects.

Enhancement of Single-Photon Purity and Coherence of III-Nitride Quantum Dot with Polarization-Controlled Quasi-Resonant Excitation.

III-Nitride semiconductor-based quantum dots (QDs) play an essential role in solid-state quantum light sources because of their potential for room-temperature operation. However, undesired background emission from the surroundings deteriorates single-photon purity. Moreover, spectral diffusion causes inhomogeneous broadening and limits the applications of QDs in quantum photonic technologies. To overcome these obstacles, it is demonstrated that directly pumping carriers to the excited state of the QD reduces the number of carriers generated in the vicinities. The polarization-controlled quasi-resonant excitation is applied to InGaN QDs embedded in GaN nanowire. To analyze the different excitation mechanisms, polarization-resolved absorptions are investigated under the above-barrier bandgap, below-barrier bandgap, and quasi-resonant excitation conditions. By employing polarization-controlled quasi-resonant excitation, the linewidth is reduced from 353 to 272µeV, and the second-order correlation value is improved from 0.470 to 0.231. Therefore, a greater single-photon purity can be obtained at higher temperatures due to decreased linewidth and background emission.

CsPbI3/N-GQDs dual layer phosphor-converted white-LEDs with ultrahigh luminous efficiency and color rendering index

Phosphor-converted LEDs or pc-LEDs, as a solid-state lighting source, are attractive for next-generation display technologies because of their energy savings, and green environmentally friendly nature. Recently, white LEDs are being produced commercially by coating blue LED (440–470 nm) chips with various yellow-emitting phosphors. However, the LEDs produced by this technique often exhibit high correlated color temperature (CCT) and low color rendering index (CRI) values, due to sufficient red spectral components not being present, and thus aren’t suitable for commercial grade white illumination. To circumvent this drawback, our work reports for the first time the use of blue and green-emitting nitrogen-functionalized graphene quantum dots (GQDs) coupled with red-emitting CsPbI3 NCs for phosphor-based LED applications. We deployed near-UV to visible excitable red-emitting perovskite CsPbI3 nanocrystals which contribute toward the red spectral component, thus greatly improving the CRI of the LEDs. CsPbI3 nanocrystals are optically excited by nitrogen-functionalized GQD with blue and green emissions in a remote double-layer phosphor stack technique. This double phosphor layer stacking greatly improves both the CRI and luminous efficiency of radiation (LER), which usually has a trade-off in previously reported phosphor stacks. A CCT of ∼5182 K providing daylight white tonality, with superior CRI (∼90%) and ultrahigh LER (∼250 lumens/watt) are reported, which are significantly higher than the established benchmarks.