Orange Phosphor Research Articles

Highly efficient orange and white electrophosphorescence from solution-processible iridium(III) complexes

The luminescent properties of two cyclometalated iridium complexes containing 2-phenylbenzothiazole ligand were investigated. With diphenylamino groups in the ligands, these iridium complexes can form neat films by spin coating their solutions. It is also possible to prepare their doped films in small molecular host matrix N,N ′-dicarbazolyl-4,4′-biphenyl by spin coating. Partially solution-processed organic light-emitting diodes (OLEDs) were fabricated with a luminance efficiency of 20.18 cd A −1 (7.81%), which is even higher than the vacuum-deposited device data for these two complexes, and also better than those for other solution-processed iridium dopant/small molecular host systems. The two-element white OLEDs containing these orange phosphors and traditional blue-emitting iridium in N,N ′-dicarbazolyl-4,4′-biphenyl host also exhibited high efficiency of 12.39 cd A −1 . It is suggested that the incorporation of the diphenylamino substituents and thus the good hole-injecting and solution processing ability of these iridium complexes are responsible for the good performance. Two iridium complexes decorated by diphenylamino substituents in cyclometalating ligands are suitable for solution processing to fabricate monochromic and white organic light-emitting diodes, which exhibit even better performance than their vacuum-deposited devices or other solution-processed iridium phosphors/small molecular host systems. • The electrophosphorescence of two iridium complexes containing 2-phenylbenzothiazole ligands are studied. • The incorporation of arylamino groups in ligands makes these complexes solution-processible. • High-performance orange and white organic light-emitting diodes were realized with these iridium complexes as doped emitters.

Spectral tuning of the n-UV convertible oxynitride phosphor: orange color emitting realization via an energy transfer mechanism

Near-UV convertible Eu(3+)-activated orange oxynitride phosphors have been obtained via a Ce(3+)→ Tb(3+)→ Eu(3+) energy transfer mechanism. The Tb(3+) ions play the role of an energy transfer bridge to connect the Ce(3+) and Eu(3+) ion pairs, and an optimal concentration of the Tb(3+) ion is necessary for maximum intensity of the Eu(3+) ion emission.

Tunable orange red phosphors: S2−-doped high temperature phase Ca3SiO4Cl2:Eu2+for solid-state lighting

S2−-doped high temperature phase (HTP) Ca3SiO4Cl2:Eu2+ is synthesized by one-step solid-state reaction at 1020 °C under H2(5%)/N2(95%) reducing atmosphere, using CaSO4 as the S source for sulfuration. Remarkable red shift of the emission spectra of S2−-doped HTP Ca3SiO4Cl2:Eu2+ is observed, comparing with Ca3SiO4Cl2:Eu2+. This is attributed to the crystal field splitting effect and nephelauxetic effect by S2− doping. The competition of the two effects also changes the excitation spectra, showing first red then blue shift. The color chromaticity of S2−-doped HTP Ca3SiO4Cl2:Eu2+ shows that it can be used as an efficient orange red phosphor for solid-state lighting.

Luminescence properties of a novel orange emission long persistent phosphor CaO:Sm3+

A novel Sm3+-doped CaO phosphor was synthesized by a traditional high temperature solid-state reaction method. The luminescence properties were studied and orange long afterglow was observed for the first time. The dependence of photoluminescence (PL) and long afterglow (LAG) properties on Sm3+ contents were investigated systematically. The optimal concentrations of Sm3+ ions for the best PL and LAG properties were experimentally to be 0.4 and 0.3mol%, respectively. After irradiation by 254nm for 3min, the duration of orange afterglow can last nearly 40min. The traps caused by the incorporation of Sm3+ ions are responsible for the generation of orange LAG. The mechanism of LAG was also illustrated briefly.

Utilizing Tb3+ as an energy transfer bridge to connect Eu2+–Sm3+ luminescent centers: realization of efficient Sm3+ red emission under near-UV excitation

The Eu(2+) → Tb(3+) → Sm(3+) energy transfer scheme has been proposed to realize the sensitization of Sm(3+) ion emission by Eu(2+) ions. Following this energy transfer model, near-UV convertible Sm(3+)-activated orange phosphors have been obtained in Sr3Y(PO4)3:Eu(2+), Tb(3+), Sm(3+) powders.

Orange Emission from (Ba1-XSrX)4Al2S7:Eu2+ Thioaluminate Phosphors with Visible Light Excitation

Solid solutions of (Ba1-XSrX)4Al2S7 (X = 0.2 to 0.6) novel thioaluminate compound were synthesized, whose crystal structure was determined. The crystal structure of the (Ba1-XSrX)4Al2S7 solid solution is related to that of monoclinic Ba4Ga2S7 consisting of isolated Ga2S7 units. However, the local structures around Ba/Sr in (Ba1-XSrX)4Al2S7, such as coordination number and one unusually long bond (d(Ba,Sr)–S > 4 Å) in 7- and 8-coordinated (Ba,Sr)–S, are different from those in Ba4Ga2S7. Eu2+-activated (Ba1-XSrX)4Al2S7 exhibited orange emission with a peak maximum at 594 nm and a corresponding excitation band at 300 to 550 nm. This is the first report of an orange phosphor in the thioaluminate system. The thermal quenching of luminescence in the (Ba1-XSrX)4Al2S7:Eu2+ phosphor was comparable to that in a conventional Y3Al5O12:Ce3+ phosphor.

Spectral optimization of the color temperature tunable white light-emitting diode (LED) cluster consisting of direct-emission blue and red LEDs and a diphosphor conversion LED

The correlated color temperature (CCT) tunable white-light LED cluster, which consists of direct-emission blue and red LEDs as well as phosphor-conversion (PC) LEDs packaged by combining green and orange phosphors with a blue LED die, has been obtained by nonlinear program for maximizing luminous efficacy (LE) of radiation (LER) under conditions of both color rendering index (CRI) and special CRI of R9 for strong red above 90 at CCTs of 2700 K to 6500 K. The optimal peak wavelengths of blue LED, red LED, blue LED die, green and orange phosphors are 465 nm, 628 nm, 452 nm, 530 nm and 586 nm, respectively. The real CCT tunable PC/red/blue LED cluster with CRIs of 90~96, R9s of 90~96, CQSs of 89~94, LERs of 303~358 lm/W, and LEs of 105~119 lm/W has been realized at CCTs of 2722 K to 6464 K. The deviation of the peak wavelength should be less than ± 5 nm for blue LED die, ± 1 nm for red LED, and ± 2 nm for blue LED to achieve the PC/R/B LED cluster with high optical performance.

Color stable and low driving voltage white organic light-emitting diodes with low efficiency roll-off achieved by selective hole transport buffer layers

White organic light-emitting diodes (WOLEDs) showing high color stability, low operating voltage, high efficiency and low efficiency roll-off by adopting different hole transport buffer layers which also behaves as electron/exciton blocking layers (EBL) have been developed. The characteristics of WOLEDs based on blue–green and orange phosphors could be easily manipulated by hole transport buffer layer, which tailors charge carrier transportation and energy transfer. Our WOLEDs show low operating voltages, 100cd/m2 at 3.2V, 1000cd/m2 at 3.7V and 10000cd/m2 at 4.8V, respectively, and achieve a current efficiency of 35.0cd/A, a power efficiency of 29.0lm/W at a brightness of 1000cd/m2, and a low efficiency roll-off 8.7% calculated from the maximum efficiency value to that of 5000cd/m2.

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu3+-doped Sr3Bi(PO4)3 have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr3Bi(PO4)3:Eu3+ phosphors invariably exhibit five peaks assigned to the 5D0→7FJ (J=0, 1, 2, 3, 4) transitions of Eu3+ and have dominating emission peak at 612nm under 392nm excitation. The luminescence intensity was enhanced with increasing Eu3+ content and the emission reached the maximum intensity at x=0.05 in Sr3Bi(PO4)3:xEu3+. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392nm are also investigated. The experimental results indicate that the Eu3+-doped Sr3Bi(PO4)3 phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.

Orange phosphorescent organic light-emitting diodes with high operational stability

In this article we report on the performances of phosphorescent orange organic light-emitting diodes (OLEDs) having a high operational stability. The fabricated devices all consist of a “hybrid” structure, where the hole-injection layer was processed from solution, while the rest of the organic materials were deposited by vacuum thermal evaporation. A device stack having an emissive layer comprising a carbazole-based host TCzMe doped with the orange phosphor tris(2-phenylquinoline)iridium(III) [Ir(2-phq)3] shows improved efficiencies compared to a the same device with the standard N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) as host material. External quantum efficiency (EQE) up to 7.4% and a power efficiency of 16lm/W were demonstrated using TCzMe. Most importantly, the operational stability of the device was largely improved, resulting in extrapolated values reaching lifetimes well above 100,000h at initial luminance of 1000Cd/m2.

Improving color stability of blue/orange complementary white OLEDs by using single-host double-emissive layer structure: Comprehensive experimental investigation into the device working mechanism

In this paper, we successfully improved the spectral stability in blue/orange complementary white organic light-emitting diodes (OLEDs) by utilizing hole-type single host double emissive layer structure. The demonstrated double emissive layer structure effectively suppresses the direct recombination of electron–hole pairs on the hole-trapping orange phosphor and thus reduces the deteriorated effect of charge trapping on electroluminescence spectrum stability by controlling exciton recombination zone. It is shown that the white light emission is a cascade energy transfer process from host to blue phosphor and then to orange phosphor, which seems to be less affected by the driving conditions. Thus, the change in Commission Internationale de L’Eclairage coordinates (CIE) in the white OLEDs is less than (±0.010, ±0.007) as the voltage increases from 4V to 9V, which correspond to the luminance increasing from 200cdm−2 to about 20,000cdm−2. This is superior to that of co-doped single emissive layer devices, which show much larger CIEs variation of (±0.05, ±0.02) in the same driving voltage range. We gave detailed analysis on the exciton recombination processes and well elucidated the working mechanism of the fabricated double emissive layer structure white OLEDs.

Preparation and characterization of rare-earth-ion free and orange yellow oxyfluoride phosphors

Rare-earth-ion free luminescent materials composed of Sr3−xMxAl0.9In0.1O4F (M=Ca, Ba, 0.1≤x≤0.7) and Sr2.5M0.5Al1−yInyO4F (0.05≤y≤0.15) oxyfluorides were simply prepared by solid-state method. X-ray diffraction (XRD) patterns of the obtained oxyfluorides are exhibited for indexing peak positions. Dynamic photoluminescence (PL) spectra of defect-induced self-activating Sr2.5Ba0.5Al1−yInyO4−αF1−δ and Sr2.5Ca0.5Al1−yInyO4−αF1−δ oxyfluorides are clearly monitored along with bright orange and yellow emission lights. The relative luminescent intensity and CIE coordinates of the defect-induced Sr3−xMxAl1−yInyO4−αF1−δ phosphors are measured. These rare-earth-ion free oxyfluoride phosphors excited around 365nm light will be one of unique luminescent materials in applications of NUV-LED.

Thiazole-based metallophosphors of iridium with balanced carrier injection/transporting features and their two-colour WOLEDs fabricated by both vacuum deposition and solution processing-vacuum deposition hybrid strategy

New phosphorescent iridium(III) cyclometallated complexes bearing thiazole-based ligands (IrTZ1 and IrTZ2) have been developed. The functionalized organic ligands derived by combining the thiazolyl moiety and triphenylamino group have conferred not only favorable hole-injection/hole-transporting (HI/HT) features but also more balanced charge carrier injection/transporting traits to the as-prepared iridium(III) metallophosphors. Owing to the unique electronic structures afforded by the ligand, the orange organic light-emitting devices (OLEDs) made from IrTZ1 can furnish peak external quantum efficiency (ηext) of 14.82%, luminance efficiency (ηL) of 39.97 cd A−1 and power efficiency (ηp) of 34.95 lm W−1. Inspired by its outstanding electroluminescence (EL) performance, the orange IrTZ1 phosphor complemented with a blue phosphor FIrpic was employed to fabricate highly efficient white organic light-emitting devices (WOLEDs) with a single emission layer. Despite their simple device configuration, the optimized WOLEDs can still maintain decent electroluminescence (EL) ability with ηext of 7.20%, ηL of 18.07 cd A−1 and ηp of 19.57 lm W−1. With the aim to simplify the fabrication process of multi-layered WOLEDs, two-component WOLEDs were obtained through a novel solution processing–vacuum deposition hybrid method with the doped blue fluorescent emission layer deposited by a solution process and the orange phosphorescent emission layer made by vacuum deposition. The WOLEDs prepared using such exploratory approach can show an attractive EL performance with ηext of 9.06%, ηL of 22.72 cd A−1 and ηp of 17.28 lm W−1. All these data have indicated not only the great potential of the orange phosphor in monochromatic and white OLEDs, but also the importance of the hybrid method for simplifying WOLED fabrication.

Reddish Orange Long-Lasting Phosphorescence in KY3F10:Sm3+ for X-Ray or Cathode Ray Tubes

We report a reddish orange long-lasting phosphor of KY3F10:Sm3+ synthesized by a solid-state reaction for applications in x-ray or cathode-ray tubes. The spectrum contains a group of reddish orange emission lines originating from 4G5/2 → 6HJ transitions of Sm3+. The Judd—Ofelt theory is introduced to analyze the optical transitions of the Sm3+ ions. Moreover, phosphorescence characteristics are discussed. The energy charging and release processes of the phosphor are measured and the phosphorescence decay time with 10% of initial intensity is about 40.7 seconds. The order of kinetics and the activation energy are obtained according to the thermoluminescence curve. The phosphorescence mechanism is proposed based on structural analysis and thermoluminescence glow curve measurement.

Spectral optimization of warm-white light-emitting diode lamp with both color rendering index (CRI) and special CRI of R9 above 90

The optimal spectra of the warm-white LED (WWLED) lamp consisting of AlGaInP red LED and the p-W LED packaged by combining silicate green and orange phosphors with a InGaN blue LED die was obtained by nonlinear program for maximizing the luminous efficacy of radiation while both color rendering index (CRI) and special CRI of R9 for strong red above 90 at correlated color temeratures (CCTs) of 2700 K. The optimal peak wavelengths of red LED, blue LED die, silicate green and orange phosphors are 626 nm, 454 nm, 535 nm and 584 nm, respectively. Their optimal relative radation fluxs are 9.7%, 33.4 %, 26.1 %, 30.8 %, respectively. The real WWLED lamp with CCT of 2653 K, CRI of 90, R9 of 94 and R(9-12) of 88, as well as luminous efficacy (LE) of 80.2 lm/W have been realized. Furthermore, the WWLED lamp can realized CCT tunable warm-white-light with CRIs of 86 ∼ 93, R9s of 86 ∼ 95 and LEs of 78.2 ∼ 80.3 lm/W at CCTs of 2392 K to 3014 K by adjusting drive current of the red LED.

Sol–gel synthesis of long-lasting phosphors CdSiO3: Mn2+, RE3+ (RE = Tb, Eu, Nd) and luminescence mechanism research

Mn2+ and RE3+ (RE=Tb, Eu, Nd) co-doped CdSiO3 orange phosphors were prepared at 1050°C by a sol–gel method. The phase and crystallinity of the synthesized materials were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The luminescence characteristics were analyzed using photoluminescence (PL) spectra, afterglow decay curves, long-lasting phosphorescence spectra, and thermoluminescence (TL) spectra. Due to the difference in co-doped rare earth ionic radii, it varied greatly in trap density and trap depth caused by the different defects deriving from RE3+ ions co-doping into the CdSiO3: Mn2+ host. The afterglow intensity and time for these samples increased as follows: CdSiO3: Mn2+0.2%, Nd3+0.8%<CdSiO3: Mn2+0.4%, Tb3+0.8%<CdSiO3: Mn2+0.4%, Eu3+0.3%. CdSiO3: Mn2+0.4%, Eu3+0.3% had the best afterglow properties, which could be due to the proper traps formed by Eu3+ ions co-doping into the host. The role of RE3+ co-doped into the CdSiO3: Mn2+ matrix and the possible long-lasting phosphorescence process was also discussed in this paper.

Reddish orange long afterglow phosphor Ca 2SnO 4:Sm 3+prepared by sol–gel method

A reddish orange light emissive long afterglow phosphor, Ca 2SnO 4:Sm 3+ was prepared by sol–gel method at lower temperature. The synthesized phosphors were characterized by X-ray diffraction, scanning electron micrograph images, photoluminescence spectra, afterglow decay curves and thermoluminescence spectra. Three emission peaks locate at 565 nm, 609 nm and 655 nm corresponding to CIE chromaticity coordinates of x = 0.53 and y = 0.47, which indicates the reddish orange light emitting. The fluorescent intensity and the afterglow characteristic depends on the concentration of Sm 3+ and the optimized concentration is 1.5 mol%. The afterglow decay curves are well fitted with triple-exponential decay models. The thermoluminescence glow curves show that the Sm 3+ induces suitable trap depth and result in the long afterglow phenomenon, and the corresponding increase or decrease in afterglow is associated with trap concentration, nearly no change in trap depth. The 1.5 mol% Sm 3+-doped Ca 2SnO 4 sample has the biggest trap concentration and exhibit the best afterglow characteristic, its’ afterglow time is about 1 h. The phosphorescence mechanism of this long afterglow phosphor was discussed.

Synthesis and phosphorescence mechanism of a reddish orange emissive long afterglow phosphor Sm3+-doped Ca2SnO4

A reddish orange emissive long afterglow phosphor Ca2SnO4:Sm3+ was prepared by solid-state reaction in air atmosphere and characterized by photoluminescence, long-lasting phosphoresce. The afterglow time is more than 7 h which is the longest red or reddish orange long afterglow phosphor at the present time. The phosphorescence mechanism of the long afterglow phosphor was studied by thermoluminescence and positron annihilation lifetime experiments. The defects VCa″, structure defects Sn3+ and Sn2+ may act as hole trapping centers while the defects SmCa⋅ may act as electron trapping centers, and trapping centers play an essential role for photoenergy storage in persistent phosphors.

Synthesis and optical properties of green to orange tunable garnet phosphors for pcLEDs

Y 3− x Lu x Al 3MgSiO 12:Ce 3+ phosphors were prepared by aqueous sol–gel technique. Samples with 0.25, 0.5, 0.75 and 1 mol-% of Ce 3+ were fabricated and characterized by powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, and temperature dependent luminescence to reveal the thermal quenching. Moreover, luminous efficacies (LE), CIE 1931 color points and quantum efficiencies (QE) were calculated and discussed. XRD patterns confirmed the presence of single phase garnet for all samples independent of Ce 3+ concentration and Y/Lu ratio. Phosphors showed broad band emission in the range 500–750 nm. The emission maximum shifts from 555 to 585 nm depending on the Ce 3+ concentration and Y/Lu ratio. Quantum efficiency of the phosphors decreased with rising Ce 3+ concentration and increased with increasing Lu content.

Luminescent properties of Eu 3+-doped BaZrO 3 phosphor for UV white light emitting diode

A novel orange phosphor Eu 3+ doped barium zirconate (BaZrO 3) was synthesized by conventional solid state reaction method and its crystal structure and luminescent properties were investigated in this paper. The X-ray diffraction patterns (XRD) showed that simple BaZrO 3 phase was obtained. Monitoring at 596 nm, the excitation spectrum consisted of a broad band and a series of narrow bands and the stronger excitation peaks located at 275 and 393 nm, respectively. The emission spectrum excited by 393 nm UV light was composed of four narrow bands. The strongest emission was located at 596 nm. The appropriate concentration of Eu 3+ was 0.025 (molar fraction) for the highest emission intensity at 596 nm. The H 3BO 3 and ammonium were added as flux and the results showed that 2 wt.% NH 4F ions was the optimal flux for BaZrO 3:Eu 3+.