Kiwan Jang

To investigate the effect of co-doping on the optical properties of Eu^(2+/3+) doped in Ba₀.₉₈SiO₃:0.02Eu, the series of Ba₀.₉₆SiO₃:0.02Eu, 0.02R^+/3+ (R⁺ = Li⁺, K⁺ or Na⁺, R³⁺ = La³⁺ or Y³⁺) phosphors were synthesized using a solid-state reaction method. The excitation efficiency due to the charge transfer band (CTB) was enhanced via co-doping of R⁺ and the emission intensity due to Eu³⁺ was thus increased by 3.7 times compared with that of the single-doped Ba₀.₉₈SiO₃:0.02Eu³⁺. However, the co-doping of R⁺ does not increase the emission intensity of Eu³⁺ via the direct ⁷F₀→⁵L₆ excitation of Eu³⁺, but rather decreases it. On the other hand, the emission intensities due to Eu²⁺ were decreased via the co-doping of R⁺ but increased via the co-doping of La³⁺. The present work reveals that the optical properties of Eu³⁺ or Eu²⁺ doped in BaSiO₃ depend not on the charge state (+ or 3+) of the co-doped ions, but on the co-doped element itself.

In this work, a silicate based phosphor doped with divalent and trivalent europium (Eu^(2+/3+)) ions have been synthesized by two different synthesis processes, PGMS (propylene glycol modified silane) assisted sol-gel and solid state reaction (SSR) method. The structural, morphological and optical properties were studied in detail. The emission intensity of Li₂SrSiO₄:Eu³⁺ phosphors synthesized through the PGMS assisted sol-gel increased up to 10 times more than that prepared by SSR method. However, Li₂SrSiO₄:Eu²⁺ phosphor prepared by PGMS exhibited lower emission characteristics and decreased to one-third of that prepared by SSR. The Eu³⁺ doped Li₂SrSiO₄ synthesized by SSR method using different silicate (Si) sources revealed peculiar optical properties and this is the first kind of its report. The obtained results suggest that the optical properties of Eu^(3+/2+) doped in silicate host can be regulated by the alteration of Si source besides sample preparation method. These results open a way to understand the mechanisms responsible for such optical properties and to develop new materials for white LEDs.

Tb³⁺ and Eu³⁺ doped zinc phosphate (ZP) glasses were prepared by conventional melt-quenching technique and their photoluminescence properties were investigated in detail. For, Tb³⁺ doped glasses the intense emission was at 545 nm corresponding to ⁵D₄→⁷F₅ transition under 377 nm n-UV excitation. The optimized concentration for Tb³⁺ doped zinc phosphate glass was 3 mol% and above this concentration quenching takes place. The Eu³⁺ doped zinc phosphate glass revealed intense emission at 613 nm attributed to the ⁵D₀→⁷F₂ transition under intense 392 nm n-UV excitation. The concentration quenching phenomenon was not observed in the Eu³⁺ doped ZP glasses. The CIE chromaticity coordinates for 3 mol% Tb³⁺ and 5 mol% Eu³⁺ doped ZP glasses were found to (0.283, 0.615) and (0.652, 0.331) lying in the green and red regions, respectively. The above mentioned results indicate that the prepared glass are suitable for application in the field of lighting and display devices.

We have studied the optical properties of CaSrSiO₄:Eu²⁺ phosphors synthesized by using the conventional solid-state reaction method and the role of Eu³⁺ minority ions in those phosphors. The maximum photoluminescence integrated peak intensity was observed for the Ca_1−x Sr_1−x SiO₄:2xEu²⁺ (2x = 0.0050) phosphor. A red shift of 3 nm from 510 to 513 nm in the emission wavelength of the CaSrSiO₄:Eu²⁺ phosphors was observed with increasing Eu concentration. Under an excitation of 244 nm, the Ca_1−x Sr_1−x SiO₄:2xEu²⁺ (2x = 0.0050) phosphor showed a broad emission band at about 515 nm due to the 4f ⁶5d ¹ → 4f ⁷ transition of the Eu²⁺ and small sharp peaks at about 594, 612, and 701 nm corresponding to the 5D ₀-⁷ F _J transitions of Eu³⁺. The existence of Eu³⁺ minority ions in the phosphor resulted in a broader full width at half maximum in the emission of the phosphor at the excitation wavelength of 390 ~ 400 nm, even at low Eu concentration. The white light-emitting diodes (LEDs) were fabricated by using the CaSrSiO₄:Eu²⁺ phosphors and 400-nm GaN-based LED chips and exhibited a high color rendering index of ~ 95 and correlated color temperature of ~ 5370 K. The broad emissions of the CaSrSiO₄:Eu²⁺ phosphors combined with the GaN-based LED chips are suitable for the realization of white LEDs.

A novel attempt towards the development of Eu²⁺ doped barium silicate and strontium barium silicate has been put forth using a versatile material, namely mesoporous silica through a convenient wet-solid phase reaction. The developed phosphor can be efficiently excited in a broad spectral range of 200–500 nm, and gets emitted strongly in the green region. On introduction of strontium to Eu²⁺ doped barium silicate phosphor, a clear red shift has been recorded in the photoluminescence spectra. These mesoporous silica assisted synthesis of Ba_1.95Eu_0.05SiO₄ and Ba_0.975Sr_0.975Eu_0.05SiO₄ phosphors showed a good thermal luminescence stability and high quantum efficiency of about 85%. It has been successfully used for the fabrication of a flexible and translucent remote phosphor. The fabricated remote phosphor attached proto-type LED exhibits a very strong green emission and this can be utilized as an efficient green component for various applications apart from the white LED productions.

The inception of phosphors provoked the need of highly efficient lighting sources for the conceivable next generation applications. In this regards, a striking characteristic material namely the mesoporous silica (MPS) and their series that are quite distinct to each other in their physical properties have been synthesized by adopting a cooperative self‐assemble strategy. Utilizing it, the development of high‐performance Sr _{1− x} Ca _{1− y} Eu _{x + y} SiO ₄ phosphor was traversed using a simple wet‐solid phase process. Systematic investigations on morphological, structural, and few other physical properties were carried out. The derived results are intriguing with a crystal clear alteration in the phosphor morphology when MPS has been used as a silicate source. Subsequent luminescence studies displayed its efficient yellow‐emitting property covering the red spectral components, along with good thermal luminescence stability. Perhaps, the designed prototype LED s yielded a color correlation temperature ( CCT ) < 5000 K and color rendering index ( CRI ) > 80. Therefore, it directs the way for the fabrication of potential warm white LED s with a long‐lived emission efficacy and high thermal luminescence stability.

High-quality and monodisperse CaMoO₄:Eu³⁺,M⁺ (M = Li, Na, K) microspheres have been synthesized with the assistance of poly-(diallyldimethylammonium chloride) (PDDA) via a facile coprecipitation hydrothermal route.

The inception of a new silicate source namely mesoporous silica for the synthesis of Sr_0.975Ca_0.975Eu_0.05SiO₄phosphor shows an excellent emissive property along with the suffice red spectral components.

The optical properties and the carrier dynamics of CaSrSiO₄:Eu³⁺ phosphors synthesized by using a solid-state reaction method have been studied by means of scanning electron microscopy, X-ray diffraction, photoluminescence (PL), PL excitation, time-resolved PL, and PL quantum-yield measurements. The phosphor synthesized with a Eu concentration of 5% and sintered at 1380 °C for 2 h in air showed a high quantum yield of 88.53% and good CIE chromaticity coordinate values. The strong excitation bands observed at 395 nm (⁷F₀-⁵L₆) and 466 nm (⁷F₀-⁵D₂) lead to an intense ⁵D₀-⁷F₂ transition (614 nm). The forbidden transitions (⁵D₀-⁷F₀ and ⁵D₀-⁷F₂) were observed and showed lifetimes shorter than that of the magnetic dipole transition (⁵D₀-⁷F₁).