CIE Color Coordinates Research Articles

Synthesis, thermal and photoluminescence investigation of Tb(III) β-diketonates with 1,10-phenanthroline derivatives

The optical and photoluminescent features of octa-coordinated terbium complexes with bidentate 2-benzoylacetophenone (BAP) and 1,10-phenanthroline ancillary ligands have been thoroughly studied. Spectroscopic analyses confirm the binding of Tb3+ with BAP and heteroaromatic auxiliary moiety by means of respective oxygen and nitrogen atoms. Photoluminescence emission plots of all the complexes present sharp peak at 549 nm ascribed to 5D4→7F5 transition, which is accountable for production of green luminescence by ternary complexes upon ultraviolet irradiation. CIE color coordinates also claim green luminescent character of synthesized complexes. All the complexes were found to have high value of color purity. Complexes exhibiting green luminescence and high thermal durability could be useful in manufacturing efficient light conversion devices for lighting systems and display devices.

Modifier’s influence on spectral properties of dysprosium ions doped lead boro-telluro-phosphate glasses for white light applications

Trivalent dysprosium doped Lead boro-telluro-phosphate glasses were synthesized with varying modifiers such as Li+, Zn2+, Ca2+, Sr2+, and Ba2+ using traditional route of glass preparation (melt quenching). The basic network formation and spectroscopical aspects of the as piped outed glasses was analyzed using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), UV–vis-NIR, photoluminescence (PL) and emission decay measurements. The existence of elementary functional groups pertaining to the present glass network was explored through FTIR spectral analysis. Bonding parameters (δ) were found to analyze the bonding nature of the rare earth ions and the surrounding metal ligand site. The optical bandgap, band tailing parameter and Urbach energy was found using Tauc’s method in order to identify the transparent region of the prepared glass samples. Furthermore, the symmetry of ligands around the Dy3+ ions has been explored with absorption spectral data by inspecting the Judd-Ofelt (JO) parameters and oscillator strengths of the as-synthesized samples. The radiative properties for instance branching ratios (βR), stimulated emission cross-section (σP) and lifetime (τR) of the meta stable states are estimated to realize the novel applications. The CIE colour coordinates and Y/B ratio values were estimated employing the photoluminescence spectra, whereas the colour purity and it’s colour correlated temperature (CCT) were determined following the (x,y) values thus confirms the generation of neutral white light emitting ability of the prepped samples. The decay or lifetime analysis shows the well fitted non-exponential behavior of the present Dy3+ doped Lead boro-telluro-phosphate glasses.

Influence of the fluorine ion content on luminescence properties of the EuII+/III+-doped silicate-substituted apatite

In this study the preparation, characterization, and photoluminescence properties of the Eu3+-doped apatite compounds have been presented. The Eu3+ ion doped silicate-substituted apatite, Ca9.9Eu0.1(PO4)2(SiO4)4(OH)2−xFx where x = 0; 0.8; 1.2; 2.0, was obtained by a microwave-assisted hydrothermal method. A detailed investigation on the heat-treated samples was done by using X-ray diffraction (XRD), scanning electron microscopy energy-dispersive spectrometry (SEM-EDS), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FT-IR). The luminescence behavior of Eu3+ ion was explored based on excitation and emission spectra as well as luminescence decay profiles. The emission spectra under excitation to the charge-transfer (CT) transition shows the broad band associated with Eu2+ ion emission. The asymmetry parameter (R parameter) and CIE color coordinates were also discussed.

Multiple-Resonance Extension and Spin-Vibronic-Coupling-Based Narrowband Blue Organic Fluorescence Emitters with Over 30% Quantum Efficiency.

Achieving narrow-bandwidth emission and high external quantum efficiency (EQE) simultaneously is a challenge for next-generation blue-emitting organic light-emitting diodes (OLEDs). In this study, novel multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters are developed by fusing an indolocarbazole unit with two carbazole skeletons using para-oriented nitrogen atoms. The resulting rigid and planar π-system without electron-accepting atoms exhibits pure blue photoluminescence at 470nm, reaching a 100% quantum yield with a full-width-at-half-maximum (FWHM) of 25nm. Higher-level quantum chemistry calculations confirm an MR effect within the extended π-conjugation and an enhanced triplet-to-singlet crossover (104 s-1 ) through a reduced energy gap (ΔEST ) coupled with large spin-vibronic coupling mediated by low-lying triplet excited states. An OLED fabricated using the MR-TADF emitter with CIE color coordinates of (0.12, 0.16) exhibits a record high EQE of 30.9% and a small FWHM of 23nm. With further optimization of the device structure, a high EQE of 33.8% is achieved without additional outcoupling enhancements owing to the near-perfect horizontal alignment of the emitting dipoles.

Li6AlGd(BO3)4: Sm3+ phosphors for orange-red light sources

A new class of Li6AlGd(BO3)4: Sm3+ phosphors were prepared via solid-state-reaction method and analyzed for orange-red light sources. The structure, morphology, distribution of particles, presence of various bonds responsible for optical properties, energy-transfer among the excited Sm3+ ions and decay properties were broadly studied. Most of the intense and sharp excitation transitions of Sm3+ in LAGBSmx phosphors appear in n-UV region and the emission spectra reveal 4G5/2 → 6H5/2, 7/2, 9/2, 11/2 transitions upon 408 nm n-UV wavelength excitation. The concentration was optimized to be 1.0 mol% for efficient orange-red emission. The CIE colour coordinates were obtained as (0.611, 0.388) for LAGBSmx phosphors with a negligible change with variation in concentration of Sm3+ ions. The decay profiles were well fitted to double-exponential function showing the occupation of Sm3+ in two different sites. The transfer of energy among the excited Sm3+ ions was possible through exchange interaction at higher concentrations. The emission of orange-red light shows its proficiency for solid-state lighting devices as well as red light source replacement in the design of white-LEDs.

BiLaWO6: Er3+/Tm3+/Yb3+ phosphor: Study of multiple fluorescence intensity ratiometric thermometry at cryogenic temperatures

Highly thermally stable Er3+/Tm3+/Yb3+ tri-doped bismuth lanthanum tungstate phosphors were prepared by high temperature solid-state reaction method. The structural and morphological properties of the prepared phosphors were analysed by X-ray diffraction (XRD), Raman spectroscopy and Scanning electron microscopy (SEM) coupled with energy dispersion spectrum (EDS). Visible upconversion (UC) luminescence was measured by exciting the phosphors with 980 nm laser radiation. The dependence of the UC intensity of each emission band of Er3+ and Tm3+ ions as a function of temperature in the range from 30 to 300 K was monitored. Fluorescence intensity ratios (FIR) of thermally coupled levels (TCL) and non-thermally coupled levels (NTCL) were analysed and verified with appropriate theoretical validation. The absolute (SA) and relative sensitivities (SR) were estimated and compared with the reported systems. In the present case of BiLaWO6: Er3+/Tm3+/Yb3+, SR (0.43 % K−1) related to TCL of Er3+ UC is found to have maximum sensitivity compared to any of the NTCL combinations at 300 K. From this study we inferred that the SR values estimated from NTCL are smaller than that of TCL involved in BLW: Er3+/Tm3+/Yb3+ phosphor. The temperature dependent CIE color coordinates were also evaluated in the cryogenic temperature region.

Three-Color White Photoluminescence Emission Using Perovskite Nanoplatelets and Organic Emitter.

Three organic blue-light-emitting tetraphenylethylene (TPE) derivatives that exhibit aggregation-induced emission (AIE) were used as additives in the preparation of inorganic perovskite-structured green-light-emitting materials for three-color white-light emission. For these organic–inorganic light-emitting materials, two-color (blue and green) light-emitting films based on the CsPbBr3 perovskite-structured green-light-emitting inorganic material were prepared. The three TPE derivatives were prepared by varying the number of bromide groups, and a distinct AIE effect was confirmed when the derivatives were dissolved in a water–tetrahydrofuran mixed solvent containing 90 vol% water. When 0.2 molar ratio of the 1,1,2,2-tetrakis(4-bromophenyl)ethylene (TeBrTPE) additive was mixed with nanocrystal-pinning toluene solvent, the green-light-emission photoluminescence quantum efficiency (PLQY) value at 535 nm was 47 times greater than that of the pure bulk CsPbBr3 without additives and a blue emission at 475 nm was observed from the TeBrTPE itself. When a CBP:Ir(piq)3 film was prepared on top of this layer, three PL peaks with maximum wavelength values of 470, 535, and 613 nm were confirmed. The film exhibited white-light emission with CIE color coordinates of (0.25, 0.36).

A heterovalent doping strategy induced efficient cyan emission in Sb3+-doped CsCdCl3 perovskite microcrystal for solid state lighting

Metal halides can produce a broadband emission spectrum of self-trapped excitons (STEs) with a large stokes shift because they have strong electron-phonon coupling and soft lattice. In this study, CsCdCl3:xSb3+ perovskite microcrystals were prepared using a simple co-precipitation strategy at room-temperature. Their composition, morphology and phase structure were characterized by EDS, XPS, SEM and XRD. The result showed that the structure of the CsCdCl3:xSb3+ perovskite microcrystals was hexagonal. In terms of luminescence, the un-doped CsCdCl3 sample showed a quite broadband emission from the host STEs with a large Stokes shift of 340 nm. The PLE and PL of the CsCdCl3:0.007Sb3+ sample show two absorptions at the wavelength of 300 and 355 nm, which is because of the 1S0 → 1P1 and 1S0 → 3P1 transitions of Sb3+ ions and the enhanced cyan emission from STEs emission of [SbCl6] octahedra induced by a heterovalent doping strategy, respectively. In addition, in the PL spectra, there are two luminescence centers in the CsCdCl3:xSb3+ samples. The emission peak at 500 nm is higher than that at 600 nm, which can be attributed to the STEs of [SbCl6] and the two face-sharing octahedra [Sb2Cl9], respectively. The formation of STEs can be demonstrated by the large S value. The CsCdCl3:xSb3+ samples undergo two thermal processes, with an activation energy of 127 meV (Ea2) at a high temperature and 101 meV (Ea1) at a low temperature. Finally, they have good thermal and anti-water stability, and thus can be possibly applied in white LED with CIE color coordinates of 0.4119 and 0.3897, the CCT of 3227 K and CRI of 79.3.

Photoluminescence assessment of Ba2-xEuxSiO4 phosphor prepared through a solid phase reaction technique using silica nanoparticles as a precursor

Generally, garnets-based phosphors are being employed in the Phosphor converted white emitting light (pc-WLED) technology. But the deficiency of red spectral components in them makes silicate-based phosphors to be successful. Our study reports the preparation of novel single-phased Ba2-xEux3+SiO4 phosphor obtained by varying dopant (Eu3+) concentration via simple dry solid-phase reaction method. Here, we have used silica nanoparticles as silicate precursor owing to their optical tunability and emissive properties which in turn depend on the occupancy of dopant in the cation site of crystal and morphology, A detailed analysis of the crystal phase and morphology of the silica nanoparticle assisted Ba2-xEux3+SiO4 phosphor (BSS) has been reported. To evaluate the colour output and tunability, the luminescence properties including excitation and emission spectra, asymmetric ratio and concentration quenching were also investigated. The obtained results indicate a rectangular-shaped morphology of BSS with red emission precisely peaked at 592 and 617 nm under the excitation wavelength of 280 nm. The optimum concentration for the luminescence quenching was found to be 7 mol% of Eu3+ in BSS phosphor and was successfully taken for further theoretical experimentations. The critical transfer distance was found to be 1.1 nm. The CIE colour coordinates (x, y) were calculated to be (0.63,0.36). The developed phosphor is found to be a potential candidate for providing enough emission at the red spectral region.

Highly efficient and thermally stable red emitting CaGdMgNbO6:Mn4+ double perovskites for indoor plant growth LEDs

Nowadays, more and more attention has been paid to artificial lighting sources for plant growth. In this paper, transition metal Mn4+ activated CaGdMgNbO6 (CGMNO:Mn4+) red phosphor was prepared high temperature solid state method. The crystal structure and cell parameters of novel CGMNO host were analyzed. The experimental results indicated that CGMNO:Mn4+ phosphor exhibit an emission band (701 nm), which belongs to the 2Eg→4A2g transition of Mn4+. The concentration quenching occurs when Mn4+ doping concentration is greater than 0.5 mol%. The variable temperature emission spectra proved that the emission intensity of CGMNO:0.005Mn4+ at 423 K maintained 75.2 % of that at 298 K. The CIE color coordinates and IQE of CGMNO:0.005Mn4+ are (0.7136, 0.2863) and 49.45 %, respectively. Finally, a LED device was packaged with CGMNO:0.005Mn4+ phosphor and a high-power chip (440 nm), the LED device shows stable electroluminescence intensity under different currents driving. All the results indicate that phosphors are suitable for lighting contemporary plant growth.

Visual and instrumental coverage error of two dental shade guides: an in vivo study

ObjectivesThis study aims to evaluate in vivo the color agreement between natural teeth and dental shade guides by means of visual and instrumental coverage error (mathrm{CE}) index.Materials and methodsThe color of the middle third of 735 incisors was visually determined by two evaluators using the Vita Classical (VC) and Vita 3D Master (V3DM) shade guides. The color match between the natural tooth and the shade tab was rated as poor (P), good (G), or optimum (O) by each observer. CIE color coordinates of the target teeth and shade tabs of VC and V3DM were instrumentally measured using a clinical spectrophotometer. Visual ({mathrm{CE}}_{mathrm{V}}) and instrumental ({mathrm{CE}}_{mathrm{I}}) coverage error indexes were computed using CIELAB and CIEDE2000 metrics for both shade guides. For {mathrm{CE}}_{mathrm{V}} calculation, only the concordant inter-observer determination on tooth shade rated as O–O or O–G was used. The results were evaluated using perceptibility (PT, {mathrm{Delta E}}_{mathrm{ab}}^{*}= 1.2, {mathrm{Delta E}}_{00}= 0.8) and acceptability (AT, {mathrm{Delta E}}_{mathrm{ab}}^{*}= 2.7, {mathrm{Delta E}}_{00}= 1.8) color thresholds for dentistry.ResultsVC and V3DM exhibited {mathrm{CE}}_{mathrm{I}} (2.5, 3.2, and 3.2, 2.7 CIELAB units; 1.9, 2.3, and 2.8, 2.4 CIEDE2000 units, respectively, for O–O and O–G match) and {mathrm{CE}}_{mathrm{V}} (4.7, 4.8, and 4.1, 4.6 CIELAB units; 3.3, 3.4, and 3.4, 3.6 CIEDE2000 units, respectively, for O–O and O–G match) values greater than 50:50% AT for both color difference formulas. {mathrm{CE}}_{mathrm{I}} contributes more than 50% (53.2–82.4% range) to the {mathrm{CE}}_{mathrm{V}} value. This contribution depends on the shade guide used and the quality of the visual rating.ConclusionsThe evaluated shade guides exhibited visual coverage errors above acceptability thresholds, largely due to the contribution of the instrumental coverage error to the visual coverage error.Clinical relevanceIt necessary to further improve commercially available dental shade guides to facilitate achievement of satisfactory esthetics results in clinical practice.

Achieving crimson red emission of europium (III) complexes with β-keto acids and ancillary ligands for their applications in optoelectronic devices and biomedical domain

ObjectiveIn this present work, the fabrication of europium (III) complexesdone using β-keto acid as main organic ligand and nitrogen donor chelates as ancillary ligands adopting grinding technique to investigate their applications in lighting devices, lasers, solar cells, semiconductors and bio-medical field. MethodsEuropium (III) complexes were probed employing multiple analytical and spectroscopic techniques such as EDAX mapping, elemental analysis, thermo-gravimetric analysis, ultraviolet-visible spectroscopy (UV-Vis), Nuclear magnetic resonance (NMR), infrared spectroscopy (IR) and photoluminescence (PL) studies. The biological activities such as anti-oxidant and antimicrobial assays were carried out utilizing DPPH and tube dilution method respectively. ResultsThe characteristic peak of europium (III) complexes documented at 616 nm was accountable for scarlet luminescence of these complexes. Color purity, CIE color coordinate and CCT were estimated to enable these complexes for display devices. The refractive index and energy band gap analysis portrays the applicability of these complexes in semiconductors and solar cells. Judd – Ofelt parameter shows the highly sensitive environment surrounding the europium (III) ion in complexes. The radiative parameters were determined which shows the applicability of these complexes as laser media. The quantum efficiency, decay time, branching ratio results their use in optoelectronic devices. Biological studies indicate better results for complexes than ligand in pharmaceuticals. Future prospectiveThe outcomes of investigation proclaimed the future prospective of the synthesized complexes in optoelectronics, lasers and display devices. Moreover, complexes can be probed further for biomedical purposes.

Luminescence properties and energy transfer of Ce3+/Eu3+ doped GSBA glass

Through the method of conventional high-temperature melting, Ce3+/Eu3+doped GeO2-SiO2-BaO-Al2O3 (GSBA) glasses were fabricated. Photoluminescence spectrum, Fourier transform infrared spectroscopy, absorption spectrum, fluorescence attenuation time and CIE color coordinates were tested to investigate the optical properties and structure of glass. Using the formula of Dexter's energy transfer, the energy transfer from Ce3+ to Eu3+ was studied. The band gap as well as spacing between rare earth ion were obtained by theoretical calculation. The results show that the optimal cerium ion concentration of the Ce3+ doped and Ce3+/Eu3+ co-doped GSBA glass was consistent, which is 0.3 mol%. For the samples only doped with Ce3+, there has no significant changes of glass structure with increasing Ce3+ concentration, and multiple ligands of [GeO4], [GeO6], [SiO4], [SiO4]&[GeO4], [AlO4] and [AlO6] co-existed in glass structure. It is proved that there is energy transfer from Ce3+ to Eu3+ and the form of energy transmission is electric quadrupole-quadrupole transfer. What's noteworthy is that in Ce3+/Eu3+ double-doped glass, the prepared glass material can emit white light through changing the doped concentration of Eu3+ ion, and color temperature is all below 3300 K, which proves the application potential of Ce3+/Eu3+ co-doped germanosilicate glass in the field of warm white LED.

Synthesis and luminescent properties of single white Ba3BP3O12:Eu3+,Dy3+ luminescent material for WLEDs

Due to the promising prospects of near-ultraviolet excitation of single-substrate white LED phosphors, a series of Ba3BP3O12:Eu3+,Dy3+ single white emitting phosphors were prepared by the conventional high temperature solid-state method in this article. This paper systematically studied the crystal structure, microscopic morphology, energy transfer mechanism and emission spectrum of the sample, and analyzed the effects of different temperature, holding time, charge compensator and rare earth ion doping on the luminescence performance of the sample. The CIE color coordinates were also calculated. The results show that Ba3BP3O12:Eu3+,Dy3+ phosphor can be used as a luminescent material on a near-ultraviolet excited white light LED.

New deep blue fluorophores based on benzo[d]thiazole group as acceptor core: Theoretical, synthesis, photophysical and electroluminescent investigation

Deep-blue organic emitters have attracted considerable attention from both industrial as well as academic research in organic light-emitting diodes (OLEDs). In this context, three novel deep blue fluorophores based on benzothiazole 2-(4'-(1,4,5-triphenyl-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)benzo [d]thiazole (PHBISN), 2-(4'-(1-(4-(tert-butyl)phenyl)-4,5-diphenyl-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)benzo [d]thiazole (PTBISN) and 2-(4'-(4,5-diphenyl-1-(3-(trifluoromethyl)phenyl)-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)benzo [d]thiazole (m-CFBISN) were designed and synthesized. The fluorophores were structurally characterized and a detailed computational study reveals the compounds with wide energy gap (>3eV). The thermal properties, photophysical and electronic properties were systematically investigated. Photoluminescence and electroluminescence study shows fluorophores with deep blue emission. Novel synthesized fluorophores exhibit good performance for deep-blue solution-processed OLEDs. The doped device based on PTBISN shows the highest performance with deep blue electroluminescent and maximum EQE 1.5% with CIE color coordinates of (0.15, 0.08), which is near to the blue standard (0.14, 0.08) of the National Television System Committee (NTSC).

Photophysical investigations of red light emanating Eu(III) complexes with dioxoester functionalized ligand for optoelectronic applications

Europium complexes attracted generous interest devoted to their red colored emission for illuminising the grounds of organic light-emitting diodes. In this series, five europium complexes (C1-C5) have been synthesized with Ethyl 4-(4-methoxyphenyl 2, 4-dioxobutanaote) (dioxoester) as primary ligand and neocuproine (neo), 2, 2′-bipyridyl (bipy), bathophenanthroline (batho) and 1, 10-phenanthroline (phen) as ancillary ligands. All these complexes are characterized by adopting various investigative techniques. They show europium-centered luminescence as a characteristic red colored emission peak at 618 nm due to (5D0-7F2) -transition. The luminescence lifetime and internal quantum efficiencies of complexes are predicted by using photophysical data and Judd-Ofelt analysis. The monoexponential behavior of the decay curve suggests the presence of a single chemical atmosphere in the inner coordination sphere of the europium ion. TG/DTG analysis reveals the thermal stability of complexes up to 245 °C. The CIE color coordinates, color purity and asymmetric ratio of complexes confirm the emission in the red region of the visible spectrum.

Influence of coordinating environment on photophysical properties of UV excited sharp red emitting material: Judd Ofelt analysis

The photophysical and optoelectronic characteristics of a series of ternary europium complexes having general formula [Eu(TFNB)3L] were estimated in detail. The synthesized octa coordinated complexes have different heteroaromatic ancillary ligand (L) i.e., 1,10-phenanthroline (Phen) derivatives. The synthesized heteroleptic europium complexes were thoroughly characterized by various techniques. Photoluminescence emission spectra specify that β-diketone ligand has efficiently sensitized Eu (III) ion through antenna effect which results in excellent luminescent intensity and long decay time. Most intense peak accredited to 5D0→7F2 is accountable for red luminescence of complexes. By investigating the PL emission data, CIE color coordinates were calculated which indicates that subsequent complexes give emission in red region. The Judd-Ofelt parameters of trivalent europium complexes were calculated and also derived theoretically via computational methods. The higher value of hypersensitive electric dipole Ω2 intensity parameter displays the existence of highly polarizable chemical environment around central metal ion. Red light emanating materials might have found good significance in solid state electronics, flat panel devices and OLEDs.

High quantum efficiency and thermal stability Sr3LiNbO6:Mn4+, Zn2+ phosphors for application in indoor plant growth lighting

New double perovskite Sr3LiNbO6:x%Mn4+ and Sr3LiNbO6:x%Mn4+, 1.25x%Zn2+ far-red-emitting phosphors were reported for the first time. The phosphors were characterized by XRD, SEM, PL, PLE, UV–vis spectroscopy, CIE color coordinate and internal quantum efficiency (IQE) measurements. Under the excitation of 365 nm light, Sr3LiNbO6:x%Mn4+ phosphors show a strong far-red emission peak at 695 nm, which is suitable for use in indoor plant application. Furthermore, by co-doping of Zn2+ ions, a more homogeneous particle size distribution was obtained and the emission intensity can raise up to 1.29 times that of Mn4+ single-doped samples. The Sr3LiNbO6:0.6%Mn4+, 0.75%Zn2+ phosphor can obtain an IQE of 78.4% and an emission intensity of 80.6% at 423 K from that at 284 K, showing a high luminous efficiency and thermal stability. Finally, a LED lamp was fabricated with the use of far-red-emitting optimized phosphor, which shows an effective promotion on growth rate and content of photosynthesis pigments of wheat. The results show that Sr3LiNbO6:Mn4+, Zn2+ phosphors may have a promising future in the field of agriculture cultivations.

Upconversion photoluminescence and radiative properties of Ba2CaWO6: Er3+ phosphors for photonic applications

Trivalent erbium doped Ba2CaWO6 phosphors were synthesized by the solid-state reaction method. Nephelauxetic ratio and bonding parameter were calculated from the absorption spectrum in order to understand the nature of Er3+ ion-ligand bonds in the prepared phosphor samples. The phenomenological Judd-Ofelt (JO) analysis has been implemented to the recorded absorption spectrum of Ba2CaWO6: Er3+ phosphors for evaluating the JO parameters. Under 980 nm laser diode excitation, Ba2CaWO6: Er3+ phosphor exhibits strong green (4S3/2 →4I15/2) and weak red (4F9/2 →4I15/2) upconversion (UC) emissions centered at 566 and 680 nm and an intense downconversion NIR emission at 1.5 μm. The UC process were assessed on the basis of power dependence of upconversion emission intensity. The significant luminescence features observed from the photoluminescence spectra of Ba2CaWO6: Er3+ phosphors that comprise of both up conversion and down conversion luminescence were discussed in detail with the aid of partial energy level diagram. The better values of radiative properties, luminescence features and CIE color coordinates suggest the suitability of Er3+ doped Ba2CaWO6 material for various photonic applications.

Tunable Dual Emission in Bi3+/Te4+-Doped Cs2HfCl6 Double Perovskites for White Light-Emitting Diode Applications.

Multicolor-emission-based single-phase white light derived from different luminescence centers is an effective way to manipulate the optical properties of halide perovskites. In this work, we developed a codoping strategy to incorporate Bi3+ and Te4+ emission centers into all-inorganic lead-free Cs2HfCl6 perovskite by a hydrothermal method. The as-prepared Bi3+/Te4+-doped Cs2HfCl6 microcrystals show bright blue (Bi3+), yellow (Te4+), and warm-white emissions (Bi3+/Te4+), respectively. The broad efficient dual emission in Bi3+/Te4+ co-doped Cs2HfCl6 is assigned to the typical 3P1 → 1S0 transition emission from Bi3+ originating from [BiHf + VCl] and self-trapped excitons (STEs) from Te4+. Moreover, the concentration-optimized Cs2HfCl6:Te4+ shows excellent antiwater stability and high photoluminescence quantum yield (PLQY) of ∼70%. Meanwhile, a white light-emitting diode (WLED) fabricated using Bi3+/Te4+ co-doped Cs2HfCl6 is close to warm white with a color rendering index (CRI) of 75.4, CIE color coordinate of (0.370, 0.393), and a correlated color temperature (CCT) of 4380 K. These results suggest that Bi3+/Te4+ co-doped all-inorganic lead-free Cs2HfCl6 is a potential single-phase white light-emitting phosphor candidate for solid-state lightings.