LED-based Solid-state Lighting Research Articles

Performance evaluation method of dye-sensitized solar cell under modulated illumination

The organic solar cell is promising as a permanent power source for indoor IoT devices. Dye-sensitized solar cells (DSSC) have been commercialized for this purpose. On the other hand, LED-based solid-state lighting is commonly chosen as the modern indoor lighting source, and most of them have a dimming function by pulse width modulation. In this article, the performance evaluation method of DSSC under modulated illumination is studied. When the modulation frequency competes with the power-line frequency set to the measurement apparatus for the rejection of the error from the power-line, the mismatch between them causes serious fluctuation in current-voltage curves. The averaging induces another problem, noticeable hysteresis. Removing the mismatch between the two frequencies is found as the proper way to eliminate the fluctuation.

Trans–cis isomerization assisted synthesis of solution-processable yellow fluorescent maleic anhydrides for white-light generation

Heterocyclic maleic anhydride derivatives have been extensively studied in natural products chemistry over the past few decades. However, their incorporation into optoelectronic devices has lagged behind that of other π-conjugated systems, and they have never been studied in white light emitting diodes (WLEDs). The development of emissive π-conjugated materials for (WLEDs) has been an emerging scientific and technological research area to replace phosphors used in LED-based solid-state lighting. Here, we demonstrate the design, synthesis and characterization of two new highly emissive alkyl-substituted bis(thienyl)maleic anhydrides (C6-Th2MA and C12-Th2MA) with favorable photophysical properties. The new core is synthesized via a novel trans-to-cis isomerization-assisted one-pot reaction, which is demonstrated for the first time in the literature for the synthesis of a bis(heteroaryl)maleic anhydride. Due to its favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively, C12-Th2MA is studied as a potential wavelength-upconverting material. A WLED fabricated by drop-casting a polymeric solution of C12-Th2MA on a blue LED (InGaN, 455nm) yields promising CIE coordinates and color-rendering index (CRI) values of (0.24, 0.20) and 65.0, respectively. Considering the simplicity of the current molecular structure and facile synthesis, alkyl-substituted bis(thienyl)maleic anhydrides stand as ideal phosphor alternatives. Therefore, the current findings may open new perspectives for the development of maleic anhydride-based small molecules for low-cost, energy-efficient, and solution-processed lighting technologies.

Combinatorial screening of luminescent and structural properties in a Ce(3+)-doped Ln-Al-Si-O-N (Ln = Y, La, Gd, Lu) system: the discovery of a novel Gd3Al(3+x)Si(3-x)O(12+x)N(2-x):Ce(3+) phosphor.

The discovery of novel phosphors for use in light emitting diodes (LED) has gained in significance because LED-based solid-state lighting applications now attract a great deal of attention for energy savings and environmental concerns. Recent research trends have centered on the discovery of novel phosphors, not on slight variations of well-known phosphors. In a real sense, novelty goes beyond simple variations or improvements in existing phosphors. A brilliant strategy for the discovery of novel phosphors is to introduce an appropriate activator to existing inorganic compounds. These compounds have structures that are well-defined in crystallographic structure databases, but they have never been considered as a phosphor host. Another strategy is to discover new host compounds with structures that cannot be found in existing databases. We have simultaneously pursued both strategies by employing metaheuristics-assisted combinatorial material search techniques. In the present investigation, we screened a search space consisting of Ln-Al-Si-O-N (Ln = Y, La, Gd, Lu), and thereby we discovered a blue-light-emitting novel phosphor, Gd3Al(3+x)Si(3-x)O(12+x)N(2-x):Ce(3+), with a monoclinic system in the C2 space group--a potential candidate for UV-LED applications.

A green-emitting α-substituted β-diketonate Tb3+ phosphor for ultraviolet LED-based solid-state lighting

The α-substituted β-diketonate [Ln(3Cl-acac)3(H2O)2] [Ln = Tb, Gd] complexes (with 3Cl-acac– being 3-chloro-2,4-pentanedionate) were characterized by elemental analysis, infrared, ultraviolet (UV)-visible and photoluminescence spectroscopies. For comparison purposes regarding photoluminescence, the well-known [Tb(acac)3(H2O)2] complex was also synthesized. By considering the phosphorescence spectra of [Gd(3Cl-acac)3(H2O)2], the effect of chloride replacement of hydrogen on the triplet state energy of the 3Cl-acac ligand was revealed. To support the interpretation and rationalization of the experimental results, Time-dependent DFT calculations were performed on Tb(3Cl-acac)3(H2O)2. Additionally, the possibility of Tb(3Cl-acac)3(H2O)2 to be used as potential green-emitting phosphor material for solid-sate light emitting diodes was evaluated. A prototype was successfully fabricated coating a near-UV LED (370 nm) with the Tb(3Cl-acac)3(H2O)2 complex.

Optimum design domain of LED-based solid state lighting considering cost, energy consumption and reliability

Design parameters of LED-based solid state lighting products are interdependent and the corresponding requirements are dictated by operating conditions. We propose a scheme to define optimum design domains of LED-based luminaires for a given light output requirement by taking cost, energy consumption and reliability into consideration. First three required data sets to define design domains are expressed as contour maps in terms of the forward current and the junction temperature (If and Tj): (1) face lumen and cost requirement as lumen/LED; (2) power consumption and energy requirement as luminaire efficacy (LE); and (3) reliability requirement as L70 lifetime. Then, the available domain of design solutions is defined as a common area that satisfies all the requirements of a luminaire. The proposed scheme is implemented for a wall wash light and the optimum design solutions are presented.

Combustion synthesis of multicomponent ceramic phosphors for solid state lighting

About 50% of the world’s need for lighting is provided by artificial lighting. For over the last decade, the world has witnessed rapid shift from conventional Hg-based lighting to LED-based solid state lighting (SSL). SSL technology extensively uses YAG:Ce3+ phosphor for production of white light emitting devices (LEDs). Part of the blue light from the (In,Ga)N LED chip is absorbed by a thin layer of Ce3+-doped YAG and is converted into yellow light. The combination of blue and yellow gives a bright white light source with an overall energy efficiency exceeding that of a compact fluorescent lamp. Several soft chemical routes have been explored for synthesis of YAG but were discarded due to their complex nature, high cost for the industrialization, phase impure materials, etc. In this paper we describe rapid one-step modified combustion synthesis of YAG:Ce3+ and related phosphors carried out at 500°C using a mixed fuel. Photoluminescence spectra of YAG:Ce3+ and LED prepared thereof are comparable with those of commercial phosphors.

Phosphors for LED-based Solid-State Lighting

The efficacy of solid-state lighting (SSL) based upon InGaN LEDs has improved by >10x over the past decade: the efficacy of cool white LEDs surpasses linear fluorescent lamp (LFLs) efficacies (>100 lm/W) and warm white 1W LEDs surpasses compact fluorescent lamps (CFLs) efficacies (>60-70 lm/W).

Red-emitting cerium-based phosphor materials for solid-state lighting applications

The discovery of phosphor materials that can be excited around 380 or 460 nm is essential for improving the efficiency and light quality of LED-based solid-state lighting devices. We have found, for the first time, a luminescent cerium compound emitting bright red light. CaSiN 2:Ce 3+ is a new phase in the calcium silicon nitride ternary system that crystallizes in a face-centered cubic unit cell with a lattice parameter of a = 14.8822(5) Å. This compound can be used for white light applications: (i) to enhance the light quality of the system based on a blue LED with a yellow/green phosphor, (ii) as the red phosphor in the UV LED plus three RGB phosphors setup or (iii) directly as a yellow phosphor with a 460 nm LED due to the emission/excitation band shift with chemical substitution.