Synthesis and luminescent properties of SrNb2O6:Eu3+ and MGe4O9 (M = Li2, LiNa and K2): Mn4+ red emitting phosphors

XUE JUNPENG 부경대학교 2017 국내석사

A series of Eu3+-doped SrNb2O6 phosphors have been successfully prepared by a high-temperature solid-state reaction technique. The as-prepared samples exhibit strong red emission peak around 612 nm, which is attributed to the 5D0-7F2 transition of the Eu3+ ion. Both the emission intensity and color rendering effect can be obviously improved in SrNb2O6:Eu3+ phosphors by self-compensation or co-doping with Li+ ions. Meanwhile, the decay time of phosphors can also be extended by charge compensation. The Judd-Ofelt theory is used to calculate the optical transition strength parameters and quantum efficiencies of the obtained samples. In addition, Eu3+ and Li+ concentration-dependent excitation and emission spectra are investigated in detail. The critical distance is determined to be about 11.48 Å and the strongest red emission intensity is achieved in the Sr0.7Nb2O6:0.15Eu3+,0.15Li+ phosphor. The CIE-1931coordinate (0.633, 0.366) of this sample is very close to that of the standard red light (0.67, 0.33). All of the results indicate that charge compensation approach can greatly improve the photoluminescence properties of Eu3+-doped SrNb2O6 phosphors, which will further promote their applications in solid state lighting. viii And others of Mn4+ions doped red-emitting phosphors such as Li2Ge4O9, LiNaGe4O9 and K2Ge4O9 red-emitting phosphors were prepared by a facile solid-state reaction technique. The crystal structure, microstructure, luminescent performance and thermal stability of the synthesized phosphors are investigated in detail with the aids of X-ray diffraction, scanning electron microscope, X-Ray photoelectron spectroscopy, diffuse reflection spectra, photoluminescence spectra, decay curves and temperature-dependent spectra. For the Mn4+ ions doped Li2Ge4O9, LiNaGe4O9 and K2Ge4O9 phosphors, the emission bands are centered at 669 (14948 cm-1), 661 (15129 cm-1) and 664 (15060 cm-1) nm, respectively. The studied compounds possess good CIE chromaticity coordinate, high color purity and high quantum yield. The crystal field strength (Dq) and Racah parameters (B and C) are estimated to evaluate the nephelauxetic effect of Mn4+ ions in Li2Ge4O9, LiNaGe4O9 and K2Ge4O9 host lattices. The calculated results well conform to show linear dependence of E(2Eg) on β1 parameter which helps to predict emission position of Mn4+ ions. In addition, the doping concentration-dependent emission spectra of K2Ge4O9:xMn4+ red-emitting phosphors are investigated to find out the optimal doping concentration. All of the results indicate that Mn4+ ions doped Li2Ge4O9, LiNaGe4O9 and K2Ge4O9 red-emitting phosphors are suitable for solid state lighting.

A research on luminescent properties of rare-earth activated oxide-based phosphors for light-emitting diodes and optical thermometry

XUE JUNPENG 부경대학교 대학원 2020 국내박사

희토류가 첨가된 형광체는 우수한 화학적 내구성과 흥미로운 발광 작용으로 고체 조명, 광학 온도계, 플라즈마 디스플레이 패널, 필드 방출 디스플레이, 액정 디스플레이, 광학 바이오마커 등 다양한 분야에서 큰 성과와 발전을 이루었다. 이 논문의 목적은 발광 다이오드와 광학 온도계를 위한 희토류가 첨가된 산화물 기반 형광체를 개발하는 것이다. 먼저, Eu3+가 첨가된 Gd2W1-xMoxO6 형광체를 고상법으로 합성했다. Mo6+이온 농도를 조절하여 연구된 샘플의 여기 밴드를 점차 긴 파장으로 이동시켰다. 376 nm 이하에서는 610 nm의 강한 적색 형광과 591 nm의 약한 황색 형광이 검출돼 Eu3+가 호스트 격자에 비반전 대칭 자리를 점유하고 있는 것으로 나타났다. Mo6+의 도판트 농도를 증가하면서 합성된 형광체의 형광강도가 크게 높아져 x = 0.95일 때 Gd2WO6:Eu3+ 화합물 보다 2.33배 높은 최적치를 달성했다. 그 결과 샘플의 양자 효율은 76.1%에 달했다. 근자외선 칩과 Gd2W0.05Mo0.95O6:Eu3+ 형광체로 구성된 적색 LED 장치가 성공적으로 제작되었다. 이러한 결과는 Eu3+가 도핑된Gd2W1-xMoxO6 형광체가 w-LED의 적색 성분으로 잠재적 가치를 가지고 있음을 확인했다. 둘째, Er3+가 첨가된 NaSrLa(MoO4)O3 형광체는 고상법에 의해 합성되었으며, 이는 377 nm 여기 하에서 Er3+ 이온의 (2H11/2, 4S3/2) → 4I15/2 전이에 따른 밝은 녹색 형광을 나타냈다. 임계거리는 25.32Å으로 추정되었고, 쌍극자-쌍극자 상호작용은 NaSrLa(MoO4)O3 호스트 격자에서 Er3+ 이온 사이의 에너지 전달에 중요한 역할을 했다. 100 mA의 순방향 바이어스 전류에서 LED 장치는 육안으로 관측할 수 있는 (0.2547, 0.5996)의 색상 좌표로 밝은 녹색 형광을 방출했다. 또한 2H11/2 및 4S3/2의 열 커플링 레벨을 기반으로 303–483 K의 온도 범위에서 제조된 형광체의 온도 감지 성능을 형광 강도비를 사용하여 연구하였다. 최대 센서 감도는 약 0.0150 K-1이었고 Er3+ 이온 농도는 연구된 샘플의 센서 감도에 크게 영향을 미쳤다. 이러한 특성은 Er3+가 첨가된NaSrLa(MoO4)O3 형광체가 발광 다이오드와 광학 온도계를 위한 이중 기능 재료라는 것을 입증했다. 그 다음, Eu3+가 첨가된 Ca3Mo0.2W0.8O6형광체는 근자외선과 청색광선 여기에 Eu3+ 이온의 5D0 → 7F2 전이에서 주로 밝은 적색 형광을 보이며 고온기술에 의해 성공적으로 제조하였다. 365, 393, 465 nm의 여기 하에서 최적의 도핑 농도는 9% mol이었고 전기 다중 극자 상호작용은 Ca3Mo0.2W0.8O6 호스트 격자에서 Eu3+ 이온 사이의 비방사 에너지 전달에 기여했다. 또한, 제조 된 w-LED는 30 mA의 주입 전류에 의해 구동 될 때 우수한 CIE 좌표, 높은 연색지수 및 낮은 상관 색온도와 같은 우수한 성능으로 따뜻한 백색광을 방출했다. 궁극적으로, 온도에 대한 감쇠 시간의 반응에 따라 298–573 K의 온도 범위에서 생성 된 형광체의 열측정 성능이 연구하였습니다. 연구된 형광체의 최대 센서 감도는 523 K에서 최대 1.16% K-1에 도달했다. 이러한 성과들은 Eu3+가 첨가된Ca3Mo0.2W0.8O6형광체가 발광 다이오드와 광학 온도계의 유망한 후보임을 나타낸다. 나아가 고상법으로 Bi3+/Eu3+가 첨가된GdNbO4 형광체 시리즈를 준비했다. 308 nm 여기 하에서 Bi3+에서 Eu3+ 이온으로의 에너지 전달은 쌍극자-사중극자 상호작용 메커니즘에 속하며, GdNbO4:Bi3+/Eu3+ 화합물들이 조정 가능한 다중색 형광을 나타낼 수 있게 하였다. 획득한 샘플의 온도에 따른 광 발광 방출 및 내수성 거동을 상세하게 조사하였다. 우리는 Bi3+와 Eu3+ 이온 사이의 다양한 열 퀀칭 성능과 그 특징적인 색 발광의 장점을 최대한 이용하여 고감도 비침전 광학 온도계를 설계했다. 최종 화합물의 최대 절대 및 상대 센서 민감도는 각각 0.0367 K-1과 3.81% K-1이었다. 위의 특징들은 Bi3+/Eu3+가 첨가된 GdNbO4 형광체를 비접촉 온도 측정을 위한 잠재적 발광 물질로 사용할 수 있음을 나타냈다. 마지막으로 Eu2+/Eu3+가 첨가된SrAl2Si2O8 형광체는 4f65d →4f7이온의Eu2+ 전이에서 발생하는 청색 형광과 Eu3+ 이온의 5D0 → 7FJ 전이에서 발생하는 적색 형광을 고상법에 의해 합성되었다. 도핑농도가 3 mol%일 때 Eu2+와 Eu3+ 이온의 형광강도는 도판트 함량이 증가하면서 증가했고 최대치에 도달했다. 또한 Eu2+ 및 Eu3+ 이온의 다양한 열적 거동에 기초하여 SrAl2Si2O8:Eu2+/Eu3+ 형광체의 열 성능이 형광 강도비에 의해 조사되었다. 최대 절대 감도와 상대 감도는 각각 0.056 K-1과 0.30% K-1로 583 K의 온도였다. 이외에도 온도에 대한 감쇠 시간의 다양한 반응을 분석하여 Eu2+와 Eu3+ 이온의 온도 성능도 298-583 K의 온도 범위에서 논의하였다. 연구된 형광체의 최대 상대 민감도는 573 K에서 최대 0.22% K-1에 달했다. 이러한 결과는 Eu2+/Eu3+가 첨가된SrAl2Si2O8 형광체가 비접촉 광학 온도측정 분야에서 잠재력을 가지고 있음을 시사한다. The rare-earth activated phosphors have attained great achievement and progress in various fields including solid-state lighting, optical thermometry, plasma display panels, field emission displays, liquid crystal displays and optical biomarkers due to the excellent chemical durability and intriguing luminescence behavior. The purpose of this dissertation is to develop the rare-earth activated oxide-based phosphors for light-emitting diodes and optical thermometry. A series of the 0.3Eu3+-activated Gd2W1-xMoxO6 phosphors were synthesized by a high-temperature solid-state reaction method. Adjusting the Mo6+ ion concentration, the excitation band of the studied sample was gradually shifted to longer wavelength. Under 376 nm excitation, the strong red emission at 610 nm and weak yellow emission centered at 591 nm were detected, indicating that Eu3+ occupies non-inversion symmetry sites in the host lattices. With increasing the dopant concentration of Mo6+, the emission intensity of synthesized products was greatly enhanced and achieved its optimum value when x = 0.95, which was 2.33 times higher than that of the Gd2WO6:0.3Eu3+ compounds. The quantum efficiency of Gd2W0.05Mo0.95O6:0.3Eu3+ was as high as 76.1%. A red LED device, which consisted of a near-ultraviolet chip and prepared Gd2W0.05Mo0.95O6:0.3Eu3+ phosphors, was successfully fabricated. These results confirmed that the Eu3+-doped Gd2W1-xMoxO6 phosphors had potential value as the red component for white-LEDs (w-LEDs). Secondly, Er3+‐activated NaSrLa(MoO4)O3 phosphors were synthesized by a traditional solid‐ state reaction technique, which exhibited bright green emissions ascribing to the (2H11/2, 4S3/2) → 4I15/2 transitions of Er3+ ions under 377 nm excitation. The critical distance was estimated to be 25.32 Å, and the dipole‐dipole interaction played a significant role in energy transfer between Er3+ ions in NaSrLa(MoO4)O3 host lattices. At a forward bias current of 100 mA, the LED device emitted a bright green emission with the color coordinate of (0.2547, 0.5996) that can be observed by the naked eye. Besides, based on the thermally coupled levels of 2H11/2 and 4S3/2, the temperature sensing performances of the prepared phosphors in the temperature range of 303‐483 K were studied using the fluorescence intensity ratio technique. The maximum sensor sensitivity was about 0.0150 K-1 and the Er3+ ion concentration largely influenced the sensor sensitivity of studied samples. These characteristics demonstrated that the Er3+ activated NaSrLa(MoO4)O3 phosphors were dual‐functional materials for light-emitting diodes and optical thermometry. Then, Eu3+-activated Ca3Mo0.2W0.8O6 phosphors, which presented bright red emissions mainly from the 5D0 → 7F2 transition of Eu3+ ions upon the near-ultraviolet and blue light excitation, were successfully prepared by a traditional high-temperature technology. Under the excitation of 365, 393 and 465 nm, the optimal doping concentration was 9 mol% and the electrical multipolar interaction contributed to the non-radiative energy transfer between Eu3+ ions in Ca3Mo0.2W0.8O6 host lattices. Additionally, the fabricated w-LEDs emitted warm white light with excellent performance, such as good CIE coordinates, high color rending index and low correlated color temperature, when driven by 30 mA of injection current. Ultimately, according to the response of the decay time to the temperature, the thermometric performances of the resultant phosphors in the temperature range of 298–573 K were studied. The maximum sensor sensitivity of the studied phosphors reached up to 1.16% K-1 at 523 K. These achievements revealed that Eu3+-activated Ca3Mo0.2W0.8O6 phosphors were promising candidates for light-emitting diodes and optical thermometry. We also prepared a series of Bi3+/Eu3+-activated GdNbO4 phosphors by solid-state reaction technique. Under 308 nm excitation, the energy transfer from Bi3+ to Eu3+ ions, which belonged to the dipole-quadrupole interaction mechanism, allowed the GdNbO4:Bi3+/Eu3+ compounds to display tunable multi-color emissions. The temperature dependent photoluminescence emission and water resistance behaviors of the obtained samples were investigated in detail. Taking full advantage of the diverse thermal quenching performance between Bi3+ and Eu3+ ions along with their distinct characteristic color emission, we designed a highly sensitive non-invasion optical thermometer. The maximum absolute and relative sensor sensitivities of the final compounds were about 0.0367 K−1 and 3.81% K−1, respectively. These above characteristics indicated that Bi3+/Eu3+-activated GdNbO4 phosphors can be used as potential luminescent materials for non-contact temperature measurement. Finally, Eu2+/Eu3+-activated SrAl2Si2O8 phosphors, which presented blue emission originating from 4f65d → 4f7 transition of Eu2+ ions and red emission arising from 5D0 → 7FJ transition of Eu3+ ions, were synthesized by solid-state reaction method in the air. The photoluminescence intensities of Eu2+ and Eu3+ ions increased with arising the dopant content and reached their maximum value when the doping concentration was 3 mol%. Moreover, based on the diverse thermal behaviors of Eu2+ and Eu3+ ions, the thermometric performance of the SrAl2Si2O8:Eu2+/Eu3+ phosphors were investigated by fluorescence intensity ratio technology. The maximum absolute sensitivity and relative sensitivity were 0.056 K-1 and 0.30% K-1, respectively, at the temperature of 583 K. Besides, through analyzing the various responses of the decay time to temperature, the thermometric performances of the Eu2+ and Eu3+ ions were also discussed in the temperature range of 298-583 K. The maximum relative sensitivity of the studied phosphors reached up to 0.22% K-1 at 573 K. These results suggested that the Eu2+/Eu3+-activated SrAl2Si2O8 phosphors had the potential in the field of non-contact optical thermometry.