Abstract:Nanocrystalline
powders of Eu3+ doped Gd3Ga3Al2O12 (GGAG) were prepared using
a modified Pechini method. The nanocrystals with the size from tens
to hundreds of nanometers were obtained. For growth of single crystal
GGAG:Eu the Czochralski method was utilized. The crystal structure,
grain morphology, and optical properties of GGAG doped with different
concentration of Eu3+ and calcined at different temperatures
were investigated and discussed. The impact of grain size and Eu3+ concentration on the spectroscopi… Show more
“…The sharp and strong PL peak at ∼690 nm, is related to the 4 A2g → 2 Eg transition, while the broadband is related to the 4 T2g → 4 A2g transition. It was reported elsewhere, that the PL intensity of the Cr-doped garnet may strongly depend on the particle size [34]. In this work, particularly for samples annealed at temperatures from 800 to 1000˚C, the PL intensity has almost the same intensity.…”
In the current work, YAGG:Cr3+ nanophosphors were synthesized by the Pechini method and then annealed at different temperatures in the range 800–1300 °C. The structure and morphology of the samples were characterized by X-ray Powder Diffraction (XRPD). The lattice parameters and average crystalline sizes as site occupation by Al3+ and Ga3+ ions were calculated from the Rietveld refinement data. To investigate the effect of crystalline size of the materials on their optical properties: excitation and emission spectra were recorded and analyzed. Finally, the effect of crystalline size on the probability of carrier recombination leading to PersL was determined experimentally with thermoluminescence analyses. The Tmax-Tstop method was applied to determine the trap type and particle size (calcination temperature) effect on their redistribution. A correlation between structural changes and trap redistribution was found. In particular, the extinction of high-temperature TL maximum with increasing annealing temperatures is observed, while low-temperature TL maximum increases and reaches a maximum when the lattice parameter reaches saturation.
“…The sharp and strong PL peak at ∼690 nm, is related to the 4 A2g → 2 Eg transition, while the broadband is related to the 4 T2g → 4 A2g transition. It was reported elsewhere, that the PL intensity of the Cr-doped garnet may strongly depend on the particle size [34]. In this work, particularly for samples annealed at temperatures from 800 to 1000˚C, the PL intensity has almost the same intensity.…”
In the current work, YAGG:Cr3+ nanophosphors were synthesized by the Pechini method and then annealed at different temperatures in the range 800–1300 °C. The structure and morphology of the samples were characterized by X-ray Powder Diffraction (XRPD). The lattice parameters and average crystalline sizes as site occupation by Al3+ and Ga3+ ions were calculated from the Rietveld refinement data. To investigate the effect of crystalline size of the materials on their optical properties: excitation and emission spectra were recorded and analyzed. Finally, the effect of crystalline size on the probability of carrier recombination leading to PersL was determined experimentally with thermoluminescence analyses. The Tmax-Tstop method was applied to determine the trap type and particle size (calcination temperature) effect on their redistribution. A correlation between structural changes and trap redistribution was found. In particular, the extinction of high-temperature TL maximum with increasing annealing temperatures is observed, while low-temperature TL maximum increases and reaches a maximum when the lattice parameter reaches saturation.
“…3 ). The increase of the luminescence intensity of YAGG:Ce 3+ and of YAGG:Ce 3+ ,Cr 3+ ,Pr 3+ nanophosphors with increasing annealing temperature was observed and is associated with the particle size increase 45 , 46 . The phosphors with large particle size have low specific surface area, and thus have less surface defects 52 .…”
Section: Resultsmentioning
confidence: 95%
“…S20 ). The DT decrease with increasing annealing temperatures could be explained by an increase of grain size of nanophosphors 45 . Figure 6 The luminescence decay curves of YAGG:Ce 3+ and YAGG:Ce 3+ ,Cr 3+ ,Pr 3+ nanophosphors annealed at 1100 °C.…”
Section: Resultsmentioning
confidence: 98%
“…The obtained values of cell parameter for the YAGG lattice are due to the difference in ionic radii between Ga 3+ and Al 3+ ions (Ga 3+ : 47 pm in tetrahedral site, 62 pm in octahedral site; Al 3+ : 39 pm in tetrahedral site, 53.5 pm in octahedral site) 41 and thus are in agreement with the hypothesis of formation of YAGG phase having Y:Al:Ga atomic ratio equal to 3:2:3. The cubic cell parameter (a) decreases with increasing the annealing temperature was observed even for YAG powders doped with erbium or europium 31,42 and this behaviour was attributed to the removal of vacancies or impurities [42][43][44][45][46] . It could also depend on a homogeneous disorder introduced into the lattice during the amorphous to crystalline transformation and on an imperfect local stoichiometry.…”
Section: Resultsmentioning
confidence: 98%
“…S20). The DT decrease with increasing annealing temperatures could be explained by an increase of grain size of nanophosphors 45 .…”
Co-doped Ce3+, Cr3+ and Pr3+ yttrium–aluminium–gallium garnet powders of various sizes were obtained by co-precipitation method. The microstructure and morphology were investigated by XRPD, TEM and gas porosimetry. The luminescence properties were studied by excitation and emission spectra, quantum yield and decay times. Thermoluminescence measurements were performed to evaluate the activation energy, traps redistribution and frequency factor. Limitation in the energy transfer between dopant ions in the small particles, traps depth and surface defects were considered and investigated as responsible for the quenching of persistent luminescence. The phosphors annealed at 1100 °C show the optimal persistent luminescence and nano-particle size.
Trivalent europium (Eu3+) doped phosphors usually radiate orange or red light owing to distinct transitions from the 5D0 excited level to the ground states of 7F1 and 7F2. However, Eu3+ activated phosphors with a dominant deep‐red emission due to 5D0→7F4 transition are relatively rare. In this work, the synthesis and photoluminescence properties of Ca3Al2Ge3O12:Eu3+ deep‐red phosphor with an intense 5D0→7F4 transition are reported. Irradiating this new garnet phosphor with 394 nm near‐ultraviolet light generates a dominant deep‐red emission band centered at 707 nm. The phosphor has a high internal quantum efficiency of 98.4% and excellent luminescence thermal stability, maintaining 78.8% of the room temperature emission intensity at 150 °C. Based on the unique spectral feature of this new compound, a phosphor‐converted deep‐red LED prototype device is fabricated, producing an output power of 27.3 mW with a photoelectric conversion efficiency of 4.0% at 200 mA. Plant growth experiments are also conducted to demonstrate the obvious positive effects of the fabricated deep‐red LED on plant growth, further indicating that the as‐prepared Ca3Al2Ge3O12:Eu3+ deep‐red phosphor can act as a promising luminescence converter for plant growth LED bulbs.
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