Luminescence properties and energy transfer of host sensitized CaMoO_4:Tb^(3+) green phosphors

A series of CaMoO4：xTb3＋ （x=0.01, 0.03, 0.05, 0.07, 0.09, 0.15 and 0.20） phosphors in pure phase were prepared via high temperature solid-state reaction approach. The crystal structure of the phosphors was investigated by X-ray diffraction （XRD）, and the optical properties were investigated by Fourier transform infrared spectroscopy （FT-IR）, ultraviolet-visible spectroscopy （UV-Vis） and photoluminescence （PL） spectroscopy. The PL spectra illustrated that these phosphors could be efficiently excited by the charge transfer band of the host and the energy transfer efficiency from the host to the doped activator reached 60% when the doping con- centration of the activator Th3＋ was 20 mol.%. The concentration quenching occurred at x= 10 mol.%, from which the critical distance of activator was calculated to be about 1.14 nm. The CIE coordinates were estimated to be close to the standard green value. The host sensitized samples had potential application as green phosphors.

LiZnPO_4:Tb^(3+),Ce^(3+) green phosphors with high efficiency

Tb^3＋ and Ce^3＋ co-activated LiZnPO4 phosphors with high luminescence efficiency were synthesized by a high temperature solid-state reaction at 1000 ℃ for 3 h. The XRD patterns, photoluminescence spectra and SEM were recorded and the effects ofTb^3＋and Ce^3＋ concentration, sintering condition on the luminescent properties of as-synthesized phosphors were investigated. The emission spectra under ultraviolet （200-300 nm） radiation showed a dominant peak at 543 nm attributed to the ^5D4→^7F5 transition of Tb^3＋, which was greatly enhanced by the co-doping of Ce^3＋, indicating that there occurred an efficient non-radiative energy transfer from Ce^3＋ to Th^3＋. The optimal doping concentrations of Tb^3＋ and Ce^3＋ were determined to be 9% and 10%, respectively.

Spectral Characteristics of LiSrBO_3:Tb^(3+) Green Phosphor

LiSrBO3：Tb^3＋ green phosphor was synthesized by means of a solid state reaction and its spectral characteristics were studied. The emission spectrum of LiSrBO3：Tb^3＋ consists of four major bands at 486, 544, 595 and 620 nm under the excitation of near ultraviolet irradiation, which are originated from the ^5Da→^7F6, ^5D4→^7F5, ^5D4→^7F4 and ^5D4→^7F3 characteristic transitions of Tb^3＋, respectively. Monitored at 544 nm, the excitation spectrum of the phosphor extends from 220 nm to 390 nm, with the excitation peaks centered at 242, 277, 368 and 381 nm, respectively. The effect of Tb^3＋ concentration on the emission intensity of LiSrBO3：Tb^3＋ was also investigated. The results show that firstly the intensity increases with increasing Tb^3＋ concentration, reaches a maximum value at 3%（molar fraction） Tb^3＋ and then decreases, showing a concentration self-quenching, whose mechanism is proposed as a d-d interaction based on Dexter theory. The emission intensity of LiSrBO3：Tb^3＋ was enhanced by co-doping Li^＋, Na^＋ and K^＋.

Green Emitting Phosphor M_3(PO_4)_2∶Ce, Tb (M=Mg, Ca, Sr, Ba) Prepared by Co-Precipitation Method

The M3-3x(PO4)2∶2xCe, xTb(M=Mg, Ca, Sr, Ba) phosphors were prepared by coprecipitation in this paper. Their phase structures, morphologies and luminescent properties were investigated by X-ray diffractometer, field emission scanning electron microscopy and fluorospectrophotometer. The results indicate that the Ce3+ and Tb3+ enteres the host lattice because the XRD patterns of alkaline earth phosphate show no impurity phase, the SEM shows the spherical particles with an average size about 1 μm. The emission and excitation spectra are similar to rare earth phosphate. Concentration quenching of the Sr3(PO4)2∶Ce, Tb emission intensity was not observed even when the Tb3+ increases to 0.05, while the maximum emission intensity appears when x=0.04 in M3-3x(PO4)2∶2xCe, xTb(M=Ca, Ba) emission spectrum.

Morphology and photoluminescence of BaAl_(12)O_(19):Mn^(2+) green phosphor prepared by flux method

This paper reports that the green phosphor BaAl12O19：0.1Mn^2＋ is prepared by a flux assisted solid state reaction method. The effect of flux systems on the crystal structure, morphology and luminescent properties of the phosphor are studied in detail. The samples are characterized by the application of x-ray diffraction patterns, scanning electron microscopy patterns, luminescent spectra and decay curves. The results show that a pure phase BaAl12O19 can be achieved at the firing temperature above 1300 ℃ by adding the proper flux system, the firing temperature is reduced at least 200℃ in comparison with the conventional solid state reaction method. Maximum photoluminescence emission intensity is observed at 517 nm for （AlF3＋Li2CO3） flux system under vacuum ultraviolet region （147 nm） excitation. The photoluminescence emission intensity and the decay time of these phosphor is found to be more superior to that of the corresponding sample prepared by the conventional solid state reaction method implying the suitability of this route for the preparation of display device worthy phosphor materials.

A New High Efficiency Green Luminescent Material──the System Al_2O_3-B_2O_3 Containing Ce^(3+) and Tb^(3+) Ions

To obtain high efficiency luminescent materials, the system Al2O3-B2O3 containing Ce3+ andTb3+ ions with variation of B2O3-content, has been prepared by Al2O3, H3BO3, CeO2 and Tb4O7 underreducing atmosphere at 1250i . It is notable that the brightness of the sample with appropriatecomposition is similar to that of commercial phosphorous containing Ce3+ and Tb3+, indicating that a newhigh efficency green luminescent material was obtained with appropriate B2O3-content.

Luminescence and Preparation of LED Phosphor Ca_8Mg(SiO_4)_4Cl_2∶Eu^(2+)

Calcium magnesium chlorosilicate doped by europium, Ca8Mg（SiO4）4Cl2： Eu^2＋, was prepared by the solid state reaction at high temperature. The compound obtained is pure Ca8Mg（SiO4）4Cl2 phase with cubic structure. Its average particle size is 5 μm, and it has good dispersity and morphological form. The excitation spectrum of Ca8Mg（SiO4）4Cl2： Eu^2＋ is a wide band, which covers from 270 to 480 nm. The emission spectrum is also a wide band peaked at 510 nm. The luminescent intensity reaches to the maximum when the concentration of Eu^2 ＋ is 2%. The wavelength of emission and excitation of the phosphor with various Eu^2 ＋ contents keeps constant. This spectrum range matches violet and blue LED chips very well, and its strong luminescence intensity is suitable for a green phosphor of tricolor phosphor of white light LED.

Microwave-Assisted Synthesis of LaPO_4∶Ce, Tb and Phosphor Characterizations

A novel method was devised to prepare green phosphor of LaPO4∶Ce, Tb by the combination of co-precipitation and microwave irradiation. The effective hess of microwave as pre-treated process and after process and microwave irradiation time were mainly discussed. The formation process and structure of green phosphor of LaPO4∶Ce, Tb were characterized by TG-DTA, XRD and SEM, respectively. As a result, phosphor of monoclinic structure with widely distributed particle size about 70 nm was successfully synthesized. The effect of microwave-assisted method as pretreatment and after-treatment on the structure and luminescent was studied property. Results indicate that the after-treatment by microwave would enhance the crystallinity as well as fluorescence intensity, the fluorescence intensity increased with the time of microwave pretreatment time, the high fluorescence intensity was found at 80 min pretreatment time. Morphological structure of phosphor particles prepared by two methods seemed similar. The emission spectrum and excitation spectrum of phosphor as prepared detected by spectrophotometer showed typical luminescent of green phosphor, the luminescence mechanism was preliminarily discussed.

Photoluminescence and thermal quenching properties of tunable green-emitting oxynitride (Ca_xSr_(1–x))_6Si_(25.6)Al_(6.4)N_(41.6)O_(4.4):Eu^(2+) phosphors

Green emitting Eu^2＋ doped（CaxSr（1–x））6Si（25.6）Al（6.4）N（41.6）O（4.4） phosphors with x value ranging from 0 to 0.1 were synthesized by the solid state reaction method under nitrogen atmosphere.The X-ray diffraction（XRD）patterns of the phosphors with different Ca^2＋ concentrations indicated that pure sialon phases were obtained.Crystal structure of these sialon phases was estimated to be a commensurate composite network stacking by two different types of layers.Intense and tunable green emissions with a slight red shift from 515 to 520 nm were observed with varying Ca/Sr ratios.The emission intensity decreased gradually because of the increase of the crystal splitting effect.Thermal quenching properties of the phosphors with different Ca^2＋ saturation were also discussed.The thermal stability became worse as more Ca^2＋ ions substituted for Sr^2＋ ions according to a larger Stokes shift.The solid solution phosphors could be a promising candidate for white LEDs for their interesting photoluminescence properties when the thermal stability would be improved.