Blue Light-Emitting Diode Phosphors Based upon Oxide, Oxyhalide, and Halide Hosts

Setlur, Anant; Lyons, Robert; Murphy, James E.; Kumar, N. Prasanth; Kishore, M. Satya

doi:10.1149/2.009302jss

Cited by 63 publications

(54 citation statements)

References 88 publications

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“…A higher light yield can potentially lead to better energy resolution of a scintillator. 2 The light yield, which is typically measured in terms of the number of photons per MeV of radiation energy, is given by L= S Q βE g × 10 6 photons/MeV, [3] where E g is the bandgap expressed in eV, Q is the quantum efficiency of the activator, S is the energy transfer efficiency to luminescent centers or activators, which are typically found in scintillators. βE g is the energy needed to create an electron-hole pair.…”

Section: Self-trapped and Dopant-bound Excitons As Activatorsmentioning

confidence: 99%

Using DFT Methods to Study Activators in Optical Materials

2015

ECS J. Solid State Sci. Technol.

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Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns 2 ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, which can be used to search for new materials. DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn 4+ Luminescence of materials when excited by photons or ionizing radiation is the foundation for numerous technologies, such as energy efficient lighting (fluorescent lamps and white LEDs), laser, medical imaging, and nuclear materials detection.1-3 Efficient luminescence in semiconductors and insulators usually relies on the localization of excited electrons and holes at certain impurities, which act as luminescence centers (or activators). An activator can trap electrons and holes for efficient radiative recombination and is the essential component of a phosphor or scintillator material. The commonly used activators are typically multivalent ions, which can insert multiple electronic states inside the bandgap of the host material. 45 Good examples of the multivalent ions that can act as luminescent centers are rare-earth ions (e.g., Ce 3+ , Eu 2+ ), 6-11 transition metal ions (e.g., Cr 3+ , Mn 4+ ), [12][13][14][15][16][17] and ns 2 ions (ions with outer electron configuration of ns 2 , such as Tl + , Sn 2+ ). 18-20Energy efficiency is critically important for phosphors used for lighting. To suppress the energy loss through nonradiative recombination, a phosphor is excited by directly exciting activators, not the host (see Fig. 1a). The excitation energy is less than the bandgap energy of the host but is large enough to excite the activator. Since the excitation occurs locally at the activator, the chance for the excited activator to interact with nonradiative recombination centers, such as deep defects, is small. This is important for achieving high quantum efficiencies for phosphors. In scintillators used for detecting ionizing radiation, the radiation creates charge carriers in the valence and conduction bands of the host, which are subsequently trapped by activators, leading to radiative recombination (see Fig. 1b). In scintillators, a portion of the charge carriers need to travel a certain distance before being trapped by the activators, which ...

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Section: Self-trapped and Dopant-bound Excitons As Activatorsmentioning

confidence: 99%

Using DFT Methods to Study Activators in Optical Materials

2015

ECS J. Solid State Sci. Technol.

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“…a combination of G, A, and R phosphors), cannot achieve high CRIs (R a > 88), while using a series of currently commercialized nitride red phosphors that are broad band (Ca,Sr)AlSiN 3 :Eu 2+ phosphors (peak wavelength (λ em ) = 610~660 nm, full-width at half-maximum (FWHM) > 85 nm, SCASIN family). [7][8][9][10] Here, narrow-band red phosphors are required to satisfy the spectral power distribution (SPD) of the Planckian locus, which is the reference chromaticity below a CCT of 5000 K. First, a CRI of 90.9 and LE of 81.56 lm/W at a CCT of 3510 K was obtained through combining the wide-band Y 3 Al 5 O 12 :Ce 3+ yellow with the narrow-band K 2 SiF 6 :Mn 4+ red phosphor (FWHM ~10 nm of the main peak) on a blue LED. 4 For the multi-color-single package approaches, two types of narrow-band red phosphors have been recently developed to reach a higher CRI for the warm white pc-LEDs than the pc-LEDs with wide-band nitride red phosphors.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of narrow-band red-emitting K₂SiF₆:Mn⁴⁺ phosphors for a deep red monochromatic LED and ultrahigh color quality warm-white LEDs

Kang

et al. 2015

J. Mater. Chem. C

153

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In this study, we synthesized and characterized narrow-band red-emitting K 2 SiF 6 :Mn 4+ phosphors in order to improve the color qualities of warm white light-emitting diodes (LEDs). The deep red monochromatic LED was realized through fabricating a long wavelength pass dichroic filter (LPDF)-capped phosphor-converted LED (pc-LED) with a synthesized K 2 SiF 6 :Mn 4+ phosphor. In addition, we introduced four-package white LEDs that combine InGaN blue (B) LED and LPDF-capped green (G), amber (A), and red (R) pc-LEDs to achieve the high color rendition at the warm white correlated color temperatures (CCTs, 2700 K) with the assistance of the narrow-band K 2 SiF 6 :Mn 4+ red phosphor. We compared the optical properties, including the luminous efficacy (LE), luminous efficacy of radiation (LER), color rendering index (CRI), special CRI for strong red (R 9 ), and color quality scale (CQS), of fourpackage white LEDs through varying the red pc-LED with one narrow-band red-emitting phosphor and five wide-band red-emitting phosphors. The RAGB four-package white LED using narrow-band red-emitting K 2 SiF 6 :Mn 4+ phosphor exhibited high LE (107 lm/W) and ultrahigh color qualities (CRI = 94, R 9 = 93, and CQS = 93) at a CCT of 2700 K.

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“…Recently, this kinds of red phosphors have been obtained by the co-precipitation approach with H 2 O 2 as reductant [9,19,20]. In order to synthesize high brightness phosphors, an excess of HF is often employed during the preparation process, since the high concentration of HF with toxicity and corrosivity is favorable for the formation of stable MnF 6 2À octahedral [21]. In consideration of safety, environmental protection, it is important to develop a simple and facile method to these red phosphors with lower concentration of HF.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of K2XF6:Mn4+ (X=Ti, Si and Ge) red phosphors for white LED applications with low-concentration of HF

et al. 2015

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Blue Light-Emitting Diode Phosphors Based upon Oxide, Oxyhalide, and Halide Hosts

Cited by 63 publications

References 88 publications

Using DFT Methods to Study Activators in Optical Materials

Using DFT Methods to Study Activators in Optical Materials

Synthesis of narrow-band red-emitting K₂SiF₆:Mn⁴⁺ phosphors for a deep red monochromatic LED and ultrahigh color quality warm-white LEDs

Synthesis of K2XF6:Mn4+ (X=Ti, Si and Ge) red phosphors for white LED applications with low-concentration of HF

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Blue Light-Emitting Diode Phosphors Based upon Oxide, Oxyhalide, and Halide Hosts

Cited by 63 publications

References 88 publications

Using DFT Methods to Study Activators in Optical Materials

Using DFT Methods to Study Activators in Optical Materials

Synthesis of narrow-band red-emitting K2SiF6:Mn4+ phosphors for a deep red monochromatic LED and ultrahigh color quality warm-white LEDs

Synthesis of K2XF6:Mn4+ (X=Ti, Si and Ge) red phosphors for white LED applications with low-concentration of HF

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Synthesis of narrow-band red-emitting K₂SiF₆:Mn⁴⁺ phosphors for a deep red monochromatic LED and ultrahigh color quality warm-white LEDs