Eun Kyung Ji

In-Situ Formed Type I Nanocrystalline Perovskite Film for Highly Efficient Light-Emitting Diode

Excellent color purity with a tunable band gap renders organic-inorganic halide perovskite highly capable of performing as light-emitting diodes (LEDs). Perovskite nanocrystals show a photoluminescence quantum yield exceeding 90%, which, however, decreases to lower than 20% upon formation of a thin film. The limited photoluminescence quantum yield of a perovskite thin film has been a formidable obstacle for development of highly efficient perovskite LEDs. Here, we report a method for highly luminescent MAPbBr3 (MA = CH3NH3) nanocrystals formed in situ in a thin film based on nonstoichiometric adduct and solvent-vacuum drying approaches. Excess MABr with respect to PbBr2 in precursor solution plays a critical role in inhibiting crystal growth of MAPbBr3, thereby forming nanocrystals and creating type I band alignment with core MAPbBr3 by embedding MAPbBr3 nanocrystals in the unreacted wider band gap MABr. A solvent-vacuum drying process was developed to preserve nanocrystals in the film, which realizes a fast photoluminescence lifetime of 3.9 ns along with negligible trapping processes. Based on a highly luminescent nanocrystalline MAPbBr3 thin film, a highly efficient green LED with a maximum external quantum efficiency of 8.21% and a current efficiency of 34.46 cd/A was demonstrated.

High power laser-driven ceramic phosphor plate for outstanding efficient white light conversion in application of automotive lighting

We report on Y3Al5O12: Ce3+ ceramic phosphor plate (CPP) using nano phosphor for high power laser diode (LD) application for white light in automotive lighting. The prepared CPP shows improved luminous properties as a function of Ce3+ concentration. The luminous properties of the Y3Al5O12: Ce3+ CPP nano phosphor are improved when compared to the Y3Al5O12: Ce3+ CPP with bulk phosphor, and hence, the luminous emittance, luminous flux, and conversion efficiency are improved. The Y3Al5O12: Ce3+ CPP with an optimal Ce3+ content of 0.5 mol % shows 2733 lm/mm2 value under high power blue radiant flux density of 19.1 W/mm2. The results indicate that Y3Al5O12: Ce3+ CPP using nano phosphor can serve as a potential material for solid-state laser lighting in automotive applications.

Long-term stable stacked CsPbBr3 quantum dot films for highly efficient white light generation in LEDs

We report highly efficient ethyl cellulose with CsPbBr3 perovskite QD films for white light generation in LED application. Ethyl cellulose with CsPbBr3 quantum dots is applied with Sr2Si5N8 : Eu2+ red phosphor on an InGaN blue chip, achieving a highly efficient luminous efficacy of 67.93 lm W-1 under 20 mA current.

The novel design of a remote phosphor ceramic plate for white light generation in high power LEDs

Here, we report a phosphor ceramic plate (PCP) constructed using Y3Al5O12:Ce3+ (YAG:Ce) nanoparticles (NPs) with a uniformly spherical size distribution for high-power light emitting diode (LED) applications. YAG:Ce NPs with diameters of 600 nm were synthesized using the forced hydrolysis method, and the typical excitation and emission of the PCP constructed using YAG:Ce NPs were observed on blue light emitting InGaN chips, as a conversion process for the generation of white LEDs with high luminous flux and thermal stability. In addition, for the improvement of the PCP characteristics, a novel design using graphene-embedded red phosphor (GRP) layer was utilized. The GRP-coated PCP displayed a higher CRI value of 82 and warm white light with a correlated colour temperature (CCT) of 3952 K compared to the general PCP. This type of PCP is expected to be an outstanding candidate for the production of luminescent materials in various fields of optoelectronics.

The effect of thickness on luminous properties of ceramic phosphor plate for high-power LD

In the present paper, garnet structured (YAG : Ce) ceramic phosphor plate (CPP) for high power laser diode (LD) was prepared and optical properties were analyzed. We synthesized monodispersed spherical nano-sized YAG : Ce particles by liquid phase method, fabricated phosphor ceramic plate with the addition of . and thick YAG : Ce CPPs were compared in terms of the factors of conversion efficacy, thermal quenching, luminance and correlated color temperature (CCT). In conclusion, conversion efficacy decreased by 25 % in both samples and thick sample provides better optical properties of thermal quenching, maximum light conversion efficacy and maximum luminance value.