Phosphor For w-LEDs Research Articles

Energy transfer and thermal stability of Ce3+, Tb3+ co-doped Ca3Si2O4N2 phosphors for white light-emitting diodes

Abstract A series of Ca 3 Si 2 O 4 N 2 :Ce 3+ , Tb 3+ phosphors were synthesized and their phase composition and luminescence properties were investigated. Results showed that an efficient energy transfer occurred between the Ce 3+ and Tb 3+ ions. The thermal stability of the Ce 3+ emission was dramatically enhanced upon Tb 3+ doping. The mechanism was attributed to a shift of the configuration coordinate and an increased energy barrier for thermal quenching, which resulted from the enhanced rigid structure of the host. Finally, a white light emitting diode lamp was fabricated, which exhibited excellent properties. These results indicate that Ca 3 Si 2 O 4 N 2 :Ce 3+ , Tb 3+ can serve as promising blue-green emitting phosphors for w-LEDs.

(Invited) Investigation of Thermal Quenching Process for 5d-4f and 3d-3d Luminescence

White light LEDs (light-emitting diodes) are rapidly replacing incandescent lamps and (compact) fluorescent tubes in all lighting markets (consumer, automotive, and professional). The most widely used type of white LEDs (w-LEDs) is a phosphor-converted w-LED (PC-LED), which is composed of an InGaN-based blue LED and visible light emitting inorganic phosphors, such as oxides and nitrides doped with Ce3+, Eu2+ , Mn4+ as an active center. These phosphors are required to have excellent thermal quenching behavior because the LED chip reaches temperatures up to ∼200 °C in recent high-power w-LED. In these phosphors, two processes of thermal quenching are considered generally. One is the thermally activated cross over from the excited state to the next lower state. The other is the thermal ionization from the excited state to the bottom of the conduction band (CB). In this study, we investigated the thermal quenching mechanism for the 5d-4f and 3d-3d luminescence in w-LED phosphors doped with Ce3+ or Mn4+. Ce3+-doped Y3Al5O12 garnet (yttrium aluminum garnet,YAG) is the most prominent phosphor in w-LEDs. The excellent thermal quenching behavior of the Ce3+ luminescence in YAG:Ce3+ is well established, but the mechanism for thermal quenching remains unclear. To elucidate the mechanism of thermal quenching of YAG:Ce3+, thermoluminescence excitation (TLE) spectra were recorded at room temperature and 300 °C. At room temperature, the lowest 5d1 band at 450 nm does not contribute to the charging process for TL while at 300 °C, a temperature corresponding to the onset of thermal quenching of the Ce3+ luminescence, the excitation in 5d1 band gives rise to a TL signal. This result indicates that thermal ionization is responsible for thermal quenching of the Ce3+luminescence. We also investigated the thermal quenching process for calcium aluminum magnetoplumbite, CaAl12O19, doped with Mn4+ (CAO:Mn4+), which is narrow red luminescence phosphor. We tried to understand the quenching mechanism of Mn4+ compared with the luminescence quenching properties of Mn2+. From the temperature dependence of Mn4+: 2E-4A2 red luminescence and Mn2+:4T1- 6A1 green luminescence intensities in CaAl12O19, the quenching temperatures of Mn4+ and Mn2+ are 330K and 800K, respectively. There is a big difference between the quenching temperatures of Mn4+ and Mn2+ in spite of the same host material and the similar luminescence transtion energy. The Mn4+:2E-4A2 red luminescence is quenched by the thermally activated crossover through the 4T2 excited state whose potential curve possesses a large configurational offset in a configurational coordinate diagram. Mn2+ green luminescence is also quenched by the thermally activated crossover, but the activation energy for non-radiative process is much larger than that for Mn4+ because there are no other excited states related with the quenching process.

Color tunable and white light emitting via energy transfer in single-phase BiOCl:Er3+,Sm3+ phosphors for WLEDs

Abstract BiOCl crystal shows potential as efficient optical host due to its special layered structure. Here, the luminescence properties of the Er3+/Sm3+ co-doped BiOCl phosphors as single-phase phosphors were reported. Upon near ultraviolet excitation (NUV, 380 nm corresponding the 4I15/2 → 4G11/2 transition of Er3+ ions), the phosphors exhibit the efficient characteristic emissions of Er3+ and Sm3+ ions simultaneously. The energy transfer (ET) from Er3+ to Sm3+ ions in the layered crystals has been validated by the variation of emission intensities and decay lifetimes respectively, which is ascribed to be a dipole–dipole interaction. By virtue of the ET behavior and increasing Sm3+ ion concentration, the enhancing emission intensity of Sm3+ and the tunability of emission color from yellowish-green (0.318, 0.420) to white (0.343, 0.347) are realized. The results of our work indicate that the Er3+/Sm3+ co-doped BiOCl phosphor has a promising application serving as single component white emitting phosphors for NUV excited WLEDs.

Facile ultrasound route for the fabrication of green emitting Ba2SiO4:Eu2+ nanophosphors for display and dosimetric applications

Abstract A series of Eu 2+ (1–5 mol%) activated Ba 2 SiO 4 nanophosphors were prepared by ecofriendly ultrasound assisted sonochemical route using Epigallocatechin gallate (EGCG) extract as bio-surfactant. The obtained nanophosphors were well characterized by Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) etc. The average crystallite size was estimated using Debye–Scherer's formula and Williamson–Hall (W–H) plots and were found to be in the range 20–32 nm. The photoluminescence excitation spectrum exhibited two broad bands around 330 and 370 nm ascribed to the transitions of Eu 2+ from 4f-ground state to 5d-excited state. The emission spectra showed broad band around 505 nm wavelength ascribed to 5d → 4f allowed transition of Eu 2+ ions. Thermoluminescence (TL) of Eu 2+ doped Ba 2 SiO 4 nanophosphors were investigated using γ-irradiation in the dose range1–6 kGy at a warming rate of 5 °C min −1 . The phosphors show a well resolved single glow peak at ∼175 °C. The TL intensity of 155 °C glow peak increase linearly with γ-dose and room temperature fading was ∼76% which was highly useful in radiation dosimetry. The kinetic parameters ( E , s ) were estimated and the results were discussed. The chromaticity co-ordinates of all the prepared phosphors were located in green region, as a result Eu 2+ activated Ba 2 SiO 4 was a promising single phased phosphor for WLEDs.

A potential single-component white-light-emitting phosphor CaMoO4:La3+,Dy3+: hydrothermal synthesis, luminescence properties and energy transfer

A series of Ca0.8La0.2−xMoO4:xDy3+ phosphors have been prepared by a hydrothermal method. The X-ray diffraction (XRD) analysis reveals that the crystal structures of the samples are coincided with the tetragonal CaMoO4. The introduction of La3+ and Dy3+ ions does not change the structure of the host lattice. The luminescence properties indicate that Ca0.8La0.2−xMoO4:xDy3+ exhibits a strong excitation band between 200 and 325 nm centered at 284 nm, and several sharp lines locate from 325 to 460 nm monitored by the yellow emission of 575 nm, which is matched well with the dominant emission of a UV light-emitting-diode (LED) chip. Compared with CaMoO4:0.05Dy3+ phosphors, the characteristic emission intensities of 575 nm (4F9/2→6H13/2) and 488 nm (4F9/2→6H15/2) of Dy3+ in CaMoO4:0.15La3+,0.05Dy3+ enhance obviously. When the doping concentration of Dy3+ is beyond 3%, a quenching phenomenon occurs accompanied with an energy-transfer via a dipole–dipole interaction. The energy-transfer critical distance was also calculated. The obtained CaMoO4:0.19La3+,0.01Dy3+ shows bright white emission with the Commission Internationale de L’Eclairage (CIE) color coordinates of (0.3123, 0.3434) and a color temperature of 6429 K upon nUV-light excitation of 353 nm, indicating that the obtained phosphor may be used as a single-component phosphor for W-LEDs.

Tunable emission, thermal stability and energy-transfer properties of SrAl2Si2O8: Ce3+/Tb3+ phosphors for w-LEDs

Abstract Ce 3+ /Tb 3+ ions singly and co-doped SrAl 2 Si 2 O 8 phosphors were synthesized by solid-state reaction method. The crystal structure, photoluminescence excitation and emission spectra, decay lifetime, energy transfer, quantum yield and thermal stability have been investigated in detail. The SrAl 2 Si 2 O 8 :0.04Ce 3+ and SrAl 2 Si 2 O 8 :0.04 Tb 3+ phosphors can emit blue and green light, respectively. Under 365 nm excitation, the emission color of SrAl 2 Si 2 O 8 :Ce 3+ , Tb 3+ can be adjusted from blue to green by changing the proportion of Ce 3+ and Tb 3+ ions based on the energy transfer. With constantly increasing of Tb 3+ ions concentration, the energy transfer efficiency from Ce 3+ to Tb 3+ in SrAl 2 Si 2 O 8 host increased gradually and reached as high as 82.91%, the quantum yield was about 67.37%. The energy transfer mechanism is proved to be dipole-quadrupole interaction. Over 100 °C, 90% initial emission intensity can be still remained. The above results indicate that SrAl 2 Si 2 O 8 :Ce 3+ , Tb 3+ is a potential multicolor emission phosphor for the application in w-LEDs.

Single-phased trichromatic white light-emitting Ca6BaP4O17:Sm3+, Ce3+, Eu2+ phosphor for UV-light-emitting diodes

Eu2+, Sm3+, Ce3+ co-doped single-phased tunable color conversion phosphor for W-LED was prepared by high-temperature melting under reducing atmosphere. X-ray diffraction and photoluminescence spectra were utilized to characterize the structural and luminescence properties of the as-synthesized phosphors. A strategy of Sm3+ doping was used with the aim of providing red color luminescence, with several sharp emission peaks appearing at 567, 603, 651, and 715 nm ascribed to the 4f–4f transitions of Sm3+. as well as a broad band from 420 to 580 nm due to the spectra overlap between the emission band of Ce3+ and Eu2+, corresponding to the 5d–4f transition of Eu2+ and 5d–4f transition of Ce3+. The luminescence properties of the phosphor with different molar ratios of Eu2+/Ce3+/Sm3+ were studied, and the corresponding chromaticity coordinates were calculated. The ultraviolet light-emitting diode (UV-LED)-excitable phosphors emitting white light were obtained by tuning the relative emission intensities of Eu2+, Ce3+, and Sm3+. The results indicate that the Eu2+/Ce3+/Sm3+ co-doped Ca6BaP4O17 phosphor can be used as a potential matrix material for white LED under UV-LED.

Synthesis, luminance and ultraviolet resistance of a copolymer phosphor of Eu-complex and siloxane in near UV-based LED

In copolymer phosphors with Eu(III), the majority have difficulty in resisting aging by UV light. In this paper, a novel copolymer phosphor with high thermal resistance and good ultraviolet aging resistance was synthesized by radical polymerization from the Eu-complex and siloxane. Intense red emission peaked at 613 nm, corresponding to the 5D0 → 7F2 transition of Eu(III) ions, was observed under UV excitation. The fluorescence lifetime is calculated as 0.586 ms, with a loss of 0.003 ms after aging for 150 h. The thermal stability shows excellent resistance to high temperature, and the initial decomposition temperature is 153 °C, which meets the requirement of LED operating temperature. The CIE of the LED device is (0.625, 0.308) under excitation at 365 nm. The LED device fabricated with the copolymer and a near-UV LED chip shows bright pure-red emission and good resistance to UV aging. This shows that the copolymer phosphor can be used as an efficient red phosphor in WLEDs.

Synthesis, structure, and photoluminescence properties of Ce3+ and Tb3+ doped alkaline-earth silicate Sr2MgSi2O7 phosphors for WLEDs

Abstract

Enhanced red-emitting phosphor Na2Ca3Si2O8:Eu3+ by charge compensation

A series of novel red-emitting Na2Ca3 − xSi2O8:xEu3+ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na2Ca3Si2O8:Eu3+ were characterized. Na2Ca3Si2O8:Eu3+ with self-compensated and alkali metal ions charge compensated approaches (2Ca2+→Eu3+ + M+, M = Li+, Na+, K+) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y203S:Eu3+. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.

Energy transfer and luminescence properties of Ce3+/Dy3+ co-doped Sr3SiO5 phosphors for WLEDs

Abstract The Sr 3 SiO 5 : Ce 3+ /Dy 3+ phosphors were prepared via a citrate assisted sol-gel method. The prepared samples were characterized by X-ray diffraction pattern, scanning electron microscopy, Fourier transform infrared spectroscopy and fluorescence spectroscopy. When excited with near-ultraviolet (NUV) (360 nm) irradiation, the photoluminescence emission spectra showed a broad band blue emission of Ce 3+ ions combined with the sharp emission peaks of Dy 3+ ions. Energy transfer occurred between the Ce 3+ and Dy 3+ ions and it increased with the increase of Dy 3+ ion concentration. The luminescence properties of the prepared phosphor materials could be adjusted by changing the concentration ratio of the Ce 3+ and Dy 3+ ions. The prepared phosphor materials also exhibited good thermal stability.

ChemInform Abstract: Low‐Concentration Eu2+‐Doped SrAlSi4N7: Ce3+ Yellow Phosphor for wLEDs with Improved Color‐Rendering Index.

AbstractSrAlSi4N7:0.05Ce3+,xEu2+ is a highly color‐tunable phosphor with emission shifting from 550 to 610 nm with increasing Eu2+ concentration.

Photoluminescence, energy transfer, and thermal stability of BaAl2Si2O8:Bi3+, Tb3+ phosphors for w-LEDs

Abstract A series of Tb 3+ or/and Bi 3+ doped BaAl 2 Si 2 O 8 phosphors were synthesized via solid-state method. The structure, luminescence properties and thermal stability were investigated. The optimum concentrations of Bi 3+ and Tb 3+ were 1.5 mol% and 7 mol%, respectively. Furthermore, BaAl 2 Si 2 O 8 :0.015Bi 3+ and BaAl 2 Si 2 O 8 :0.07Tb 3+ phosphors emitted blue and green light and the emission color of BaAl 2 Si 2 O 8 :Bi 3+ , Tb 3+ could be tuned from blue to green through the energy transfer. This energy transfer from Bi 3+ to Tb 3+ was confirmed and investigated by photoluminescence spectrum and decay lifetime. With constantly increasing Tb 3+ concentrations, the energy transfer efficiency from Bi 3+ to Tb 3+ in BaAl 2 Si 2 O 8 host increased gradually and reached as high as 86.54%, the quantum yield was about 44.26%. The energy transfer mechanism (Bi 3+ -Tb 3+ ) was proved to be dipole–dipole mechanism. The Tb 3+ emission intensity can be considerably enhanced when monitored at NUV (377 nm) by co-doping Bi 3+ ion. Moreover, the phosphor of BaAl 2 Si 2 O 8 :0.015Bi 3+ , 0.07Tb 3+ could exhibited strong green emission with good CIE chromaticity coordinate. The results indicate that BaAl 2 Si 2 O 8 :Tb 3+ , Bi 3+ is a potential green emitting phosphor for the application in w-LEDs.

Site distortion in Li2SrSiO4: Influence on Pr3+ emission and application in wLED

Abstract Luminescence of Pr 3+ in Li 2 SrSiO 4 showed a broader f–f emission band compared with YAG:Pr 3+ . Atom parameters of Li 2 SrSiO 4 crystal were refined to provide data for quantifying the distortion of [SrO8] polyhedron. The distortion of [SrO8] was compared with that of [YO8] polyhedron in YAG to show the different Pr 3+ environments in Li 2 SrSiO 4 and YAG. Then, Pr 3+ was co-doped with Eu 2+ in Li 2 SrSiO 4 to provide a single phosphor for wLEDs. Energy transfer processes from 5d of Eu 2+ to both 3 P 2 and 1 D 2 of Pr 3+ were observed. The interaction type between Eu 2+ –Pr 3+ was proved to be dipole-quadrupole and kinetics of the energy transfer process was discussed based on Inokuti–Hirayama model.

BPO4@B2O3 and (BPO4@B2O3):Eu3+: The novel single-emitting-component phosphors for near UV-white LEDs

Abstract Nowadays much effort has been devoted to exploring novel luminescent materials with low-cost, high stability and excellent luminescent properties. In this paper, a new kind of luminescent material BPO 4 @B 2 O 3 was prepared by using a facile method. The as-obtained samples contain numerous BPO 4 nanoparticles enclosed by amorphous and crystalline B 2 O 3 homogeneously, which exhibits a broad emission band ranging from 380 to 700 nm under near-UV irradiation. More importantly, it is worth noting that the BPO 4 @B 2 O 3 phosphor exhibits the excellent thermal quenching property, which endows it with a promising prospect as phosphors for high power white LEDs. To further promote its application as white light phosphors, Eu 3+ ions were doped into the BPO 4 @B 2 O 3 samples and prepared the (BPO 4 @B 2 O 3 ):Eu 3+ phosphors with chromaticity coordinates (0.3022, 0.3122). The corresponding packaging of LEDs indicates that both BPO 4 @B 2 O 3 and (BPO 4 @B 2 O 3 ):Eu 3+ can be considered as the promising phosphors for WLEDs.

ChemInform Abstract: A New Series of Borophosphate Phosphor Cd3BPO7:M (M: Ce3+, Tb3+, Mn2+) with Tunable Luminescence and Energy Transfer Properties.

AbstractCd3BPO7, Cd3BPO7:xCe3+ (x = 5, 7, 9, 11 mol%), Cd3BPO7:yTb3+ (y = 2, 3, 4, 6, 8, 12 mol%), Cd3BPO7.zMn2+ (z = 0.5, 0.7, 1.15, 2 mol%), Cd3BPO7:9 mol%Ce3+,yTb3+ (y = 3, 4, 6, 8 mol%), and Cd3BPO7:9 mol%Ce3+,zMn2+ (z = 0.5, 0.7, 1.15, 2 mol%) are prepared by solid state reactions of stoichiometric amounts of CdO, H3BO3, NH4H2PO4, Tb4O7, CeF3, and MnCO3 (alumina crucible, 573—1123 K, 4—12 h).

A new series of borophosphate phosphor Cd3BPO7:M (M = Ce3+, Tb3+, Mn2+) with tunable luminescence and energy transfer properties

Abstract A new series of Cd3BPO7:M (M = Ce3+, Tb3+, Mn2+) phosphors have been synthesized and characterized using X-ray powder diffraction as well as excitation and emission spectroscopy. Based on the Cd3BPO7 host, the singly doping Ce3+, Tb3+ and Mn2+ yield the blue, green and red-emitting phosphors respectively under the irradiation range from 270 to 300 nm UV. By appropriate tuning of Tb3+ or Mn2+ activator content, the emission color of the Cd3BPO7:Ce3+/M (M = Tb3+ or Mn2+) phosphors can be changed from blue to green or pink, respectively. Under UV excitation, the mixture of the as-prepared blue, green and red phosphors yields the warm white light, which exhibits their potential application as UV-convertible phosphors for WLEDs.

Evaluation of new color metrics: guidelines for developing narrow-band red phosphors for WLEDs

In this review, we summarize the recent findings on novel narrow-band red phosphors, the improved color and visual energy properties of these phosphors, and their ability to improve the optical properties of corresponding warm white pc-WLED lightings.

Analysis on stability and consistency of intensity measurement of White Light Emitting Diode phosphors

This paper focuses on the stability and consistency of intensity measurements of WLED phosphors. The quality of phosphor products are determined by the measured intensities, but in practice it is often found that intensity measurements cannot be replicated. This problem is due to the instability of test conditions (fluctuating light source power, different paring of quartz lids, etc.) A Monte Carlo ray-tracing model is applied to illustrate the differences in faculae caused by tiny quartz lid slips. The research presented would be particularly beneficial for researchers and manufactures of phosphor.

A novel coordination network of Tb(III) with 2-hydroxy-trimesic acid showing very intense photoluminescence

Abstract A novel coordination network consisting of Tb(III) ions and 2-hydroxy-trimesic acid (H4L) has been prepared and characterized using infrared spectroscopy, elemental analysis, thermogravimetric analysis and single crystal X-ray crystallography. The structure forms a rigid three-dimensional network, which is described by the formula [Tb(HL)(H2O)2]n. The compound shows emission lines characteristic for Tb(III) when excited with near-UV radiation. The quantum yield of this process is 67%, showing that the ligand acts as a highly efficient antenna for sensitizing Tb(III) emission and that the complex TbHL potentially is a good phosphor for WLED.