Color-tunable Phosphors Research Articles

Crystal structure and spectral tuning of Eu2+/Eu3+ co-activated Na2Ba1-xSrxCa(PO4)2 phosphors with high thermal stability

The coupling of UV LED chips with phosphors to produce white or color-tunable light is still a challenge. In this work, we propose a simple rare earth occupation site engineering method to adjust the valence of doped Eu ions. Based on the Ba2+ substituted by Sr2+, new Eu2+/Eu3+ co-activated Na2Ba1-xSrxCa(PO4)2 (NB1-xSxCP) phosphors were designed and successfully synthesized. In NB1-xSxCP, the Ba2+/Sr2+ site is occupied by Eu2+, while the Ca2+ site is occupied by Eu3+. The coupled broad blue 448 nm and sharp red 619 nm luminescence under 321 nm excitation has demonstrated the coexistence of Eu2+ and Eu3+. This double emission phenomenon is studied in terms of the fluorescence lifetime as well as lattice distortion induced by the substitution ions. With the increased substitution of Sr, the luminescence of NB1-xSxCP:0.03Eu2+/3+ can be tuned from blue to red crossing the warm-white region. When x = 0.3, the chromaticity coordinates is located at (0.3779, 0.2495). The integrated intensity of Na2Ba0.7Sr0.3Ca(PO4)2:0.03Eu2+/3+ at 150℃ remains 90.9 % of that at room temperature, while the chromaticity shift (ΔE) can be calculated as 15 ×10−3. The Eu2+/Eu3+ co-activated NB1-xSxCP is a potential candidate for single-phase color-tunable phosphors used for light-tunable applications due to the combining contributions from both Eu3+ and Eu2+ ions.

Efficient Energy Transfer for Near-Perfect Quantum Efficiency and Thermal Stability.

The pursuit of high-quality phosphors exhibiting swift response to near-ultraviolet (n-UV) excitation, elevated quantum efficiency (QE), superior thermal stability, and impeccable light quality has been a focal point of investigation. In this research, we synthesized a novel K2La2B2O7:Ce3+,Tb3+ (KLBO:Ce3+,Tb3+) color-tunable phosphor that meets these requirements. KLBO:Ce3+ can be stimulated efficiently by the n-UV light and shows an intense blue emission centered at 437 nm. Notably, KLBO:0.04Ce3+ exhibits exceptional internal QE (IQE = 94%) and outstanding thermal stability (I423K/I303K = 88%). Optimization of doping compositions enables efficient Ce3+ → Tb3+ energy transfer, resulting in substantial enhancements in QE and thermal stability. Specifically, KLBO:0.04Ce3+,0.28Tb3+ achieves an IQE of 98% and a thermal stability of 97%, higher than those of most phosphors of the same type. White light-emitting diodes fabricated using phosphor samples emit warm white light characterized by high Ra (Ra = 96.6 and 93.4) and low CCT (CCT = 4886 and 4400 K). This study underscores the feasibility of enhancing phosphor QE and thermal stability through energy transfer mechanisms.

Tunable emission and energy transfer of B2O3–Bi2O3–AlF3 glass system doped with Eu3+/Dy3+

The structure and luminescent properties of the B2O3–Bi2O–AlF3 glass system doped with Eu3+/Dy3+ ions in different molar ratios were studied. A series of glasses were synthesized by the conventional melt quenching technique. Glass transition and crystallization temperatures were examined by Differential Thermal Analysis (DTA) measurements. The amorphous character of the prepared samples was confirmed by the X-ray diffraction (XRD) method. Raman and FTIR spectra were collected and deconvoluted to investigate the glass micro-structure. Luminescence spectra revealed that the added rare-earth ions can be excited by a single wavelength. The emitted color can be tuned by changing the ratios of the Eu3+/Dy3+ ions and the excitation wavelength. Furthermore, the influence of the addition of AlF3 on the luminescence and decay times was investigated. In the glasses with 10 mol% AlF3 an enhancement of the emission and excitation spectra was detected. The energy transfer analysis confirms the energy transfer between Eu3+ and Dy3+ ions in the glass matrix. Additionally, the results of this study indicate that the B2O3–Bi2O–AlF3 glasses doped with Eu3+ and Dy3+ can be used as a color tunable phosphor.

Tunable luminescence in pyrochlore Lu2Sn2O7:Eu3+ nanoparticles at elevated pressure

High pressure study is crucial in chemical, physical and materials sciences for understanding phase transitions, new phase evolution and in designing pressure sensors. Utilizing the high potential of pyrochlore as luminescent sensors and its structural diversity, Lu2Sn2O7:5.0%Eu3+ (LSOE) nanoparticles (NPs) have been synthesized using a hydrothermal method and characterized at ambient condition using x-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM). The reduced intensity of hypersensitive electric dipole transitions (5D0→7F2), reduction in average luminescence lifetime, and increase in symmetry around Eu3+ has also being observed in the LSOE NPs induced by the applied high pressure. The same is reflected in color tuning from red to orange to yellow on switching pressure from low to medium to high. Lifetime spectroscopy suggests that high pressure causes site-swapping of europium ion from Lu3+ to Sn4+, which triggers change in local symmetry around Eu3+. This work will pave a newer way of designing high pressure induced color tunable phosphor, high pressure sensor and need-based site engineering in pyrochlore compounds and their nanomaterials for high pressure applications.

Electronic structure, colour-tunable emission and energy transfer in Li3Ba2Y3(WO4)8:Bi3+,Eu3+ phosphors for white light-emitting diodes.

Solid-state phosphor-converted white light-emitting diodes (pc-WLEDs) are the leading trend of the lighting industry in the 21st century. To pursue high quality WLED lighting, the development of highly efficient phosphors with tunable luminescence has become a hot research topic. Herein, we reported for the first time on Bi3+/Eu3+-doped Li3Ba2Y3(WO4)8 phosphors that exhibited tunable emission and high energy transfer efficiency of 89.90% from Bi3+ to Eu3+. The phase purity, microstructure, electronic structure and photoluminescence properties of these phosphors were studied in detail. Bi3+ and Eu3+ were effectively doped in Li3Ba2Y3(WO4)8 with an optical bandgap of 3.81 eV. The band structure and density of states were quantitatively evaluated by density functional theory simulation. At an excitation wavelength of 342 nm, the Bi3+-doped phosphor achieved yellow-green emission. By alloying Eu3+ into Li3Ba2Y3(WO4)8:Bi3+, the luminescence gradually turned red due to the energy transfer from Bi3+ to Eu3+. Moreover, the activation energy of the prepared phosphor was 0.1897 eV, demonstrating excellent thermal stability. Eventually, by combining Li3Ba2Y3(WO4)8:4%Bi3+,4%Eu3+ and a blue-emitting BAM:Eu2+ phosphor with a 365 nm ultraviolet chip, a WLED device with a high colour rendering index (Ra) of 78.7, chromaticity coordinates of (0.3401, 0.3131) and correlated colour temperature of 5080 K was successfully achieved. This work provided new insights into the design and development of color-tunable phosphors for white LEDs.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED’s and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303–483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED’s and photodynamic therapy for the cancer treatment.

UV and blue excited tunable emission of thermally stable Bi3+ sensitized Eu3+ doped calcium aluminozincate phosphor for photonic applications

Bi3+/Eu3+ co-driven calcium aluminozincate (CAZ) phosphor prepared by sol–gel route. Structural analysis was conducted based on X-ray diffractogram. Scanning Electron Microscope images were recorded using Carl Zeiss microscope. Luminescent traits of the said phosphors were identified using excitation and emission spectroscopy at room temperature and elevated temperature. The emission spectra recorded at room temperature under different excitations exhibit variation in spectral behavior. The Commision Internationale de-lElcairage coordinates shown in chromaticity diagram indicate the change in emission hue as pure blue, bluish red and finally pure red by varying the excitation wavelengths. The temperature dependent emission spectra show decrease in emission intensity with temperature and activation energy found to be 0.280 eV. The decay curves were also recorded to determine lifetime and study energy transfer between Bi3+ and Eu3+ ions. Auzel’s fit conducted based on the decay lifetimes helps in evaluating quantum efficiency theoretically. All these investigations authorize the potential of Bi3+/Eu3+ doped CAZ phosphors for their utilization as color-tunable phosphor in photonic applications.

Long wavelength emissive ZnO/CQDs phosphor with high color purity and its application in sensitive detection of cadmium (II)

Production of color-tunable emission via simple method for upcoming displays and lighting technologies, and their exceptional luminescence provide considerable potential in sensing application. As environmental pollution and diseases brought by cadmium have always been global issues, therefore, it is imperative to develop an inexpensive, quick, easy, and selective approach for detecting trace cadmium. Herein, we describe the preperation of ZnO/carbon quantum dots (ZnO/CQDs) nanocomposite that emits strongly in the yellow-orange zone with the chromaticity coordinates (0.51, 0.47) and a high color purity (CP) value of 94.3%. The as-produced ZnO/CQDs are used as a fluorescence sensor for Cd2+ via quenching mechanism due to competitive coordination between ZnO/CQDs and Cd2+ with the limit of detection (LOD) of 0.14 μM. Additionally, the suggested method can successfully detect Cd2+ in water samples, demonstrating the feasibility and potential uses of the sensing platform. This study may pave the way for the development of environmentally safe, high-performing, and inexpensive color-tunable phosphor for white LEDs and sensing applications.

A novel broad-band red K2MgSiO4:Eu2+ phosphor and defect-induced tunable emission from red to yellow

Tunable emission in red phosphors is a challenge for the application of wLED. Herein, we reported a new Eu2+ doped oxide based red K2MgSiO4:Eu2+ phosphor. Under excitation at 319 nm, the K2MgSiO4: Eu2+ phosphor exhibits a broad band red emission peaking at 648 nm with FWHM ≈231 nm. The structural and spectral analyses suggest that Eu2+ occupy K1/K3O6 sites and K2/K4O8 sites to form two Gaussian fitting emissions at 732 nm and 629 nm, respectively. To achieve tunable emission, reducing the Si content is attempted in K2MgSi1-yO4:Eu2+. As the Si content decreases from y = 0 to y = 0.04, the emission spectrum shows a blue shift from 648 nm to 523 nm. Therefore, defect-induced color-tunable phosphors from red to yellow are obtained through reducing Si content in the host. This study aims to provide a new research method to guide the development of Eu2+ doped oxide based red phosphors and design idea to obtain tunable emission of phosphors. Moreover, the defect-induced photoluminescence tuning strategy is universal to most luminescent materials.

Luminescence and energy transfer of Ce3+/Tb3+ activated fluoroborate BaGaBO3F2 as a color tunable phosphor

Ce3+/Tb3+ co-doped BaGaBO3F2 is a new rare-earth activated luminescent material with efficient green luminescence. The phosphor was synthesized via the conventional solid-state reaction and characterized by X-ray powder diffraction, photoluminescence, and decay lifetimes. The Ce3+/Tb3+ co-doped phosphor exhibits an efficient excitation between 280 and 420 nm, making it suitable for commercial near-UV chips. The 4f–5d transitions of Ce3+ sensitizer allow the phosphor to be excited by the near-UV light, resulting in green and blue luminescence from Tb3+ and Ce3+, respectively. By controlling Ce3+/Tb3+ doping, the luminescence color can be tuned from blue to green. The effective transfer of excitation energy from Ce3+ to Tb3+ of BaGaBO3F2 was confirmed by the spectral characteristics and decay lifetimes of samples with different doping concentrations. The dipole-quadrupole mechanism is responsible for the efficient energy transfer from Ce3+ to Tb3+, with a critical distance of 11.69 Å. These results demonstrate that Ce3+/Tb3+ co-doped BaGaBO3F2 is an efficient near-ultraviolet (NUV) excitation phosphor with tunable luminescence from blue to green. This material has the potential to be used as a down-conversion phosphor for NUV light-emitting diodes.

Defect engineering towards anti-temperature quenching luminescence for application in light emitting diodes

Thermal quenching (TQ) that weakens luminescent intensity is crucial for the application value of a phosphor. Here, we report a series of color-tunable phosphors Na2MgAl10O17:xEu2+ (NMA:xEu2+) from green to cyan. For optimized Eu2+ concentration of x = 0.15, its internal and external quantum efficiency can reach up to 86% and 43%, respectively. In addition, it is unexpected that NMA:0.15Eu2+ exhibits anti-temperature quenching (TQ) luminescence even up to 300 °C, which is due to the ability of the defect energy levels to counteract the usual loss of emission by TQ through EPR and TL spectral analysis. Then, a prototype w-LED lamp by using NMA:0.15Eu2+ cyan phosphor, CaAlSiN3:Eu2+ red phosphor, and 380 nm LED chip is fabricated. This work not only reports a new phosphor with high efficiency and good thermal stability of luminescence, but also brings forward a defect engineering approach for enhancing the thermal quenching resistance of a phosphor.

Tunable luminescence and efficient energy transfer investigation of a borosilicate phosphor KBSi2O6: Bi3+, Eu3+ with hypersensitive thermal quenching

Energy transfer between Bi3+ and Eu3+ has undergone substantial research but Bi3+ and Eu3+ co-doped luminescent materials with high energy transfer efficiency for temperature sensing are rarely investigated until now. Herein, Eu3+ and Bi3+ co-doped KBSi2O6 phosphors were successfully synthesized by solid-state reaction method. The phase purity structure as well as the element distribution were carefully investigated through X-ray diffraction structural refinement and energy dispersive spectrometer analysis. The characteristic luminescence property and luminescence kinetics of KBSi2O6: Bi3+, Eu3+ were investigated. By the large spectra overlap between the emission spectrum of Bi3+ and excitation spectrum of Eu3+, the energy transfer from Bi3+ to Eu3+ can be inferred. The corresponding decrease of the emission intensity and decay time of Bi3+ in KBSi2O6: Bi3+, Eu3+ provided direct evidence for the effective energy transfer from Bi3+ to Eu3+. The interaction and energy transfer mechanism between Bi3+ and Eu3+ ions were also studied. By increasing the Eu3+ concentration in KBSi2O6: Bi3+, Eu3+, the color-tunable emission from blue to red can be realized. KBSi2O6: Bi3+, Eu3+ shows hypersensitive thermal quenching behavior and the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) are determined to be 1.87 %K−1 and 2.895 %K−1, respectively. All of the above results imply that KBSi2O6: Bi3+, Eu3+ phosphor can be a color-tunable phosphor for optical temperature sensing.

Anomalous power-dependent color tuning of Er upconverting luminescence via 1530 nm excitation

The upconversion color tuning of Lanthanide ions usually requires complex core–shell structures and excitation configurations. This work presents simple Er3+ doped Yttria phosphors capable of color change through the manipulation of 1530 nm excitation intensity. Compared to the reported results of Er3+ color change from green to red with the increase in excitation intensity, the formed color-tunable phosphors show an inverse change of red to green. The color tuning mechanisms are attributed to the competition between the upward absorption and the downward decay at the Er3+ intermediate state. Finally, the potential applications of the formed color-tunable phosphors are demonstrated. This work provides a simple solution for high-performance upconversion color tuning and thus shows wide application prospects.

Highly thermally stable and tunable luminescence in microwave-assisted synthesized Na3Ca4(TeO3)(PO4)3:Dy3+,Eu3+ for ultra-high color rendering white light-emitting diodes

For the commercial application of the Eu3+-activated red phosphors in NUV (∼365 nm)-excited phosphor-converted white light-emitting diodes (pc-wLED), the serious obstacle is that they cannot be efficiently excited by ∼365 nm. To deal with the trouble, we employed the energy transfer between Dy3+ sensitizer excited by ∼365 nm and Eu3+ activator, and a color-tunable phosphor Na3Ca4(TeO3)(PO4)3 (NCTP):Dy3+,Eu3+ was prepared via a fast microwave-assisted solid-state reaction. Under the 363 nm excitation, the luminous color is adjusted to red owing to the Dy3+→Eu3+ energy transfer with high efficiency, which is controlled by the dipole–dipole interaction. Moreover, the introduction of Dy3+ sensitizers in NCTP:Eu3+ enhances the structural rigidity, resulting in high luminescence thermostability. The luminescent intensity at 423 K remains 90.7% of that at 298 K. Notably, the 365 nm chip-excited pc-wLED device assembled with NCTP:0.09Dy3+,0.4Eu3+, commercial blue BaMgAl10O17:Eu2+, and green (Ba,Sr)2SiO4:Eu2+ phosphors emits warm-white light (0.3657,0.3725) with the ultra-high Ra (94.9) and low CCT (4399 K). This work offers a feasible Dy3+→Eu3+ energy transfer path for the development of efficient Eu3+-activated red phosphor towards ultra-high color rendering pc-wLED.

Study on energy transfer and temperature sensing properties of Pb2+/Sm3+ co-doped Ba2MgY2(BO3)4

Researches on fluorescence intensity ratio (FIR) based temperature sensors have become more and more popular in recent years. Herein, we co-doped Pb2+ and Sm3+ into the host material Ba2MgY2(BO3)4 (BMYB) to prepare a new series of phosphors. The Pb2+ activated phosphor BMYB:0.03 Pb2+ presents a wide blue emission band centered at 416 nm under 278 nm laser excitation with internal quantum efficiency of 46%. In the presence of both Pb2+ and Sm3+, energy transfer will occur between them, resulting in tunable color emission. Besides, the phosphor has an absolute sensitivity of 0.96% K−1 at 575 K, which makes it an excellent candidate for temperature sensing. These findings suggest that prepared phosphor is a potential candidate for color tunable phosphor and temperature sensing material.

Structural and luminescence properties of B2O3-Bi2O3-AlF3 glass doped with Eu3+, Tb3+ and Tm3+ ions

The B2O3-Bi2O3-AlF3 glass system doped with Eu3+, Tb3+, Tm3+ and triply doped with Eu3+/Tm3+/Tb3+ ions in different molar ratios were successfully synthesized. Glass transition and crystallization temperatures were examined by Differential Scanning Calorimetry (DSC) measurements. X-ray Diffraction (XRD) confirmed the amorphous character of the samples. Fourier Transform Infrared Spectroscopy (FTIR) revealed that the glass matrix consists of [BO3] and [BO4] structural units, while X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of AlF3. An increase in luminescence spectra intensity was detected by Photoluminescence Spectroscopy (Pl), due to the presence of 10 mol% of AlF3. The RE3+ ions embedded in the glass matrix can be simultaneously excited by a single UV light. According to the CIE results the emitted color can be tunable by varying the excitation wavelength and sample composition. The presented results confirm that the proposed glass system could be a candidate for color-tunable phosphors in LEDs.

Tunable upconversion in ZnAl2−xGaxO4:Er,Yb phosphors by modulating the Al/Ga ratio and application in optical thermometry

This work demonstrated the usability of spinel for a color tunable phosphor triggered by compositional modulation in Al/Ga ratio and laser power along with feasibility for non-contact optical thermometry.

Designing dual-emission phosphors for temperature warning indication and dual-mode luminescence thermometry.

Color tunable phosphors of Mn4+ and Tb3+ co-doped double-perovskite SrGdLiTeO6 (SGLT) were synthesized in this work. The crystal parameters and photoluminescence performances were investigated in detail. By taking advantage of the different thermal quenching strengths between Mn4+ and Tb3+ ions, the emission color of SGLT:0.7%Mn4+/1%Tb3+ changed from red to green, which could be used for high-temperature temperature warning indication. Moreover, according to the luminescence intensity ratio (LIR) technique, wide temperature-range optical thermometry was developed and further, the maximum relative sensitivity (SR1) value of the SGLT:0.7%Mn4+/5%Tb3+ phosphor was determined to be 1.49% K-1 at 560 K. On the other hand, the sensing properties were also analyzed based on the temperature-dependent lifetime method. The most interesting thing is that the maximum SR2 value reached 1.88% K-1 at 573 K. This work proved that the Mn4+ and Tb3+ co-doped double-perovskite SrGdLiTeO6 could be potentially used in temperature warning indication and high sensitivity luminescence thermometry.

A new melilite-type rare-earth borate CdTbGaB2O7 and multicolor tunable emission in the CdTb1-xSmxGaB2O7 (0 ≤ x ≤ 0.2) phosphors.

A new mixed metal borate, CdTbGaB2O7, was successfully synthesized using the high-temperature solution method and its crystal structure was determined by single-crystal X-ray diffraction with the following unit-cell data: P4̄21m, a = b = 7.3487(1) Å, c = 4.7247(1) Å, V = 255.150(9) Å3, and Z = 2. It belongs to a new member of the melilite family, which features a 3D framework consisting of alternately stacked [Ga(B2O7)]n5n- tetrahedral layers and (Cd2+/Tb3+) cationic layers that are interconnected via B(Ga)-O-(Cd/Tb) bridges. In addition, the solid solutions of CdTb1-xSmxGaB2O7 (0 ≤ x ≤ 0.2) were prepared via the solid-state reaction method. The combined techniques of XRD, SEM, IR/Raman, XPS and PLE/PL were employed to characterize the products. It was found that the CdTb1-xSmxGaB2O7 phosphors simultaneously showed green emission of Tb3+ at 545 nm and orange emission of Sm3+ at 603 nm under excitation at 370 nm. The emission color can be adjusted from green to orange-red by varying the Sm3+ doped content via an energy transfer mechanism. For CdTb0.995Sm0.005GaB2O7, a QY of 13.22% was obtained, and its emission intensity at 423 K was 94% of that at 303 K. These results show that the prepared materials can act as potential color-tunable phosphors for UV w-LEDs.

Luminescence and energy transfer of a novel BaCeF5: Tb3+, Eu3+ color-tunable phosphor

A novel BaCeF5: Tb3+, Eu3+ color-tunable phosphor was synthesized using a co-precipitation-hydrothermal method. The photoluminescence (PL) spectra revealed that BaCeF5 has its own fluorescence effect as blue emission. The energy transfer process from Ce3+ to Tb3+ was achieved after doping with Tb3+, enabling the conversion of the luminous color from blue to green. By doping Eu3+ in BaCeF5: 10 %Tb3+, the energy transfer process from Tb3+ to Eu3+ was further realized and the transition from green to orange light continued in the phosphor. Finally, the energy transfer mechanism of Ce3+-Tb3+-Eu3+ in the BaCeF5: Tb3+, Eu3+ samples was explored. The results indicate that by varying the Tb3+ and Eu3+ concentrations, the phosphor transition from blue - green - orange light can be performed, which is a promising material to be applied to multicolor emission modulated luminescent materials as well as incandescent lamp materials.