Enhancing Solar Energy Conversion Efficiency: A Tunable Dual-Excitation Dual-Emission Phosphors and Time-Dependent Density Functional Theory Study

The concept of dual-excitation dual-emission (DE2) phosphors for the enhancement of solar energy conversion is introduced in this work. Doping alkaline earth cations as an aggregated energy trap within the sulfur host in a controlled manner resulted in the DE2 phosphors with tunable fluorescent emission properties. It had been found the Ca0.6Sr0.4S:0.005Cu+,0.001Eu2+ phosphor is the optimal DE2 composition. We demonstrated by field testing results their potentials in enhancing sunlight harvesting to increase production of agricultural plants. Time-dependent density functional theory calculations provide insights about their excitation and emission mechanisms. These DE2 phosphors can be applied to a variety of fields, as additives to increase production of agricultural crops, as nanosensor and biolabeling materials for ultrasensitive or green-sensitive detection of biological species such as antibodies, DNA and cells, and other places

Ultrafast Self-Crystallization of High-External-Quantum-Efficient Fluoride Phosphors for Warm White Light-Emitting Diodes

In this study, we used HF (as good solvent) to dissolve K₂GeF₆ and K₂MnF₆ and added ethanol (as poor solvent) to cause ultrafast self-crystallization of K₂GeF₆:Mn⁴⁺ crystals, which had an unprecedentedly high external quantum efficiency that reached 73%. By using the red phosphor, we achieved a high-quality warm white light-emitting diode with color-rendering index of <i>R</i>_a = 94, <i>R</i>9 = 95, luminous efficacy of 150 lm W^–1, and correlated color temperature at 3652 K. Furthermore, the good–poor solvent strategy can be used to fast synthesize other fluorides

Ultrafast Self-Crystallization of High-External-Quantum-Efficient Fluoride Phosphors for Warm White Light-Emitting Diodes

In this study, we used HF (as good solvent) to dissolve K₂GeF₆ and K₂MnF₆ and added ethanol (as poor solvent) to cause ultrafast self-crystallization of K₂GeF₆:Mn⁴⁺ crystals, which had an unprecedentedly high external quantum efficiency that reached 73%. By using the red phosphor, we achieved a high-quality warm white light-emitting diode with color-rendering index of <i>R</i>_a = 94, <i>R</i>9 = 95, luminous efficacy of 150 lm W^–1, and correlated color temperature at 3652 K. Furthermore, the good–poor solvent strategy can be used to fast synthesize other fluorides

Suppression of Thermal Quenching for CsPbX₃ (X = Cl, Br, and I) Quantum Dots via the Hollow Structure of SrTiO₃ and Light-Emitting Diode Applications

All-inorganic perovskite quantum dots (PQDs, CsPbX3, X = Cl, Br, and I) show outstanding application prospects in the field of photoelectric devices. In recent years, the development of PQDs has greatly improved their stability to water, oxygen, and light. However, thermal quenching of PQDs greatly limits their practical application. Herein, we embed PQDs into ATiO3 (A = Ca, Ba, and Sr) of three different mesoporous spherical structures to explore the effect on thermal quenching of PQDs. Because of the unique mesoporous hollow microsphere structure and low thermal conductivity of SrTiO3, it can effectively block the heat transfer and improve the thermal quenching of PQDs. The photoluminescence (PL) intensity of CsPbBr3@SrTiO3 composites is 72.6% of the initial intensity after heating to 120 °C. Moreover, the PL intensity of CsPbBr3@SrTiO3 composites remains about 80% of the initial value even when stored in air for 20 days or irradiated by 365 nm UV light for 48 h. A neutral white light-emitting diode is assembled by a blue chip, CsPbBr3@SrTiO3 composites, and red phosphor of K2SiF6:Mn4+, which has a color temperature of 5389 K and a color gamut covered 133% of National Television Standards Committee (NTSC)

Effectively Leveraging Solar Energy through Persistent Dual Red Phosphorescence: Preparation, Characterization, and Density Functional Theory Study of Ca₂Zn₄Ti₁₆O₃₈:Pr³⁺

To effectively leverage and convert cheap, abundant, and environmentally friendly solar energy is still an unaccomplished endeavor. In this work, we prepare and characterize the long-lasting red-light-emitting, single-phase Ca2Zn4Ti16O38 phosphor by the sol−gel method with nonstoichiometry or addition of H3BO3 as flux. Excitation and emission mechanisms are proposed and supported by the computational results from density functional theory. Phase identification of powders was performed by X-ray powder diffraction analysis, confirming the existence of single-phase Ca2Zn4Ti16O38 crystals in samples of every series. Unit cell parameters of the crystal were subsequently determined, together with its excitation spectra in the blue-green region with the maximum peak at 474 nm monitored by 644 nm light. The corresponding emission spectra showed a wide emission range with two narrow bands at 614 nm (1D2 → 3H4) and 644 nm (3P0 → 3F2) after the addition of H3BO3. If excited at 474 nm, the phosphor displays a superlong afterglow with the emission peak at 614 nm, enabling it to be a novel persistent red long phosphor for visible-light conversion. Luminescent properties of the phosphor were thoroughly examined. The mechanism of the dual persistence phosphorescence originated at 614 and 644 nm wavelengths induced by two separate kinds of doping defects was proposed. Density functional theory calculations under the periodic boundary condition provide insights about their excitation, emission, and long-lasting phosphorescence mechanisms

From Nonluminescence to Bright Blue Emission: Boron-Induced Highly Efficient Ce³⁺-Doped Hydroxyapatite Phosphor

Photoluminescence quantum efficiency (QE) and thermal stability are important for phosphors used in phosphor-converted light-emitting diodes (pc-LEDs). Hydroxyapatite, Ca5(PO4)3OH, is generally not used as host for phosphors, because the OH– group in the host will lead to a high vibrational frequency around the activators and reduces the luminescent efficiency or even quenches the emission. In this work, strong blue emission at 450 nm appears after introducing boron atoms into Ce3+-doped hydroxyapatite under excitation of a UV light. Analyses suggest that B atoms enter into the host structure, which lead to the modification of crystal structure and the formation of vacancies of O and H to compensate charge mismatch. The decrease of OH– groups around Ce3+ ion on Ca (3) site is responsible for the appearance of strong blue emission. The absolute QE value of the best blue-emitting phosphor is ∼92%, and the emission intensity at 150 °C remains 81% of that at room temperature. The emission peak and International Commission on Illumination (CIE) coordinates hardly change upon increasing temperature. The results suggest that boron-modified hydroxyapatite phosphor could be a candidate for UV-LED-pumped white phosphor-converted LEDs. This strategy may provide a new insight into the exploration of phosphors’ hosts and other functional materials

Isolated Coordination Polyhedron Confinement in ABP₂O₇:Mn²⁺ (A = Ba/Sr; B = Mg/Zn)

Many research efforts have focused on designing new inorganic phosphors to meet different application requirements. The structure–photoluminescence relationship between activator ions and the matrix lattice plays an irreparable role in designing target phosphors. Herein, a series of ABP2O7:Mn2+ (A = Ba/Sr; B = Mg/Zn) phosphors are prepared for a detailed study on the relationship between the luminescence performance and spatial structure and symmetry of the doping site of Mn2+. Due to the weak interaction between nearest B–B pairs, [BO5] is defined as an isolated coordination polyhedron whose structure and symmetry directly influence the photoluminescence of Mn2+. The emission wavelength of Mn2+ is ∼620 nm when it occupies the triangular bipyramid [MgO5] in BaMgP2O7. When Mn2+ occupies the quadrangular pyramid-typed [MgO5] or [ZnO5] in SrMgP2O7, SrZnP2O7, and BaZnP2O7, the emission wavelengths peak at ∼670 nm. We propose a conception of isolated coordination polyhedral confinement to clarify the luminescence performance of Mn2+ in the fivefold coordination configuration with different geometries, which has great theoretical research significance for designing inorganic phosphors

Changing Ce³⁺ Content and Codoping Mn²⁺ Induced Tunable Emission and Energy Transfer in Ca_2.5Sr_0.5Al₂O₆:Ce³⁺,Mn²⁺

A series of color-tunable Ce³⁺ single-doped and Ce³⁺, Mn²⁺ codoped Ca_2.5Sr_0.5Al₂O₆ phosphors were synthesized by a high-temperature solid-state reaction. The crystal structure, luminescent properties, and energy transfer were studied. For Ca_2.5Sr_0.5Al₂O₆:Ce³⁺ phosphors obtained with Al­(OH)₃ as the raw material, three emission profiles were observed. The peak of photoluminescence (PL) spectra excited at ∼360 nm shifts from 470 to 420 nm, while that of the PL spectra excited at 305 nm stays unchanged at 470 nm with the increase of Ce³⁺ content. Furthermore, the peak of PL spectra is situated at 500 nm under excitation at ∼400 nm. The relationship between the luminescent properties and crystal structure was studied in detail. Ce³⁺, Mn²⁺ codoped Ca_2.5Sr_0.5Al₂O₆ phosphors also showed interesting luminescent properties when focused on the PL spectra excited at 365 nm. Obvious different decreasing trends of blue and cyan emission components were observed in Ca_2.5Sr_0.5Al₂O₆:0.11Ce³⁺,<i>x</i>Mn²⁺ phosphors with the increase in Mn²⁺ content, suggesting different energy transfer efficiencies from blue- and cyan-emitting Ce³⁺ to Mn²⁺. Phosphors with high color-rendering index (CRI) values are realized by adjusting the doping content of both Ce³⁺ and Mn²⁺. Studies suggest that the Ca_2.5Sr_0.5Al₂O₆:Ce³⁺,Mn²⁺ phosphor is a promising candidate for near UV-excited w-LEDs

Redistribution of Activator Tuning of Photoluminescence by Isovalent and Aliovalent Cation Substitutions in Whitlockite Phosphors

Many strategies, including double substitution, addition of charge compensation, cation-size-mismatch and neighboring-cation substitution, have contributed to tuning photoluminescence of phosphors for white light-emitting diodes. These strategies generally involve modification of a certain special site where the activator occupies; tuning strategy based on multiple cation sites is very rare and desirable. Here we report that isovalent (Sr²⁺) and aliovalent (Gd³⁺) substitutions for Ca²⁺ tune the photoluminescence from one band to multiple bands in whitlockite β-Ca_3–<i>x</i>Sr_<i>x</i>(PO₄)₂:Eu²⁺ and β-Ca_{3–3<i>y</i>/7}Gd_2<i>y</i>/7(PO₄)₂:Eu²⁺ phosphors. The saltatory variation of the emission spectra is caused by the removal of Eu²⁺ from the site M(4) to other sites. Moreover, we found the mechanisms of dopant redistribution tuning the luminescence are different. The incorporation of Gd³⁺ makes the site M(4) empty according to the scheme 3Ca²⁺ = 2Gd³⁺ + □, while Sr²⁺ substitution causes the cation sites to be enlarged due to cation size mismatch. Additionally, the influence of the cation substitutions on the photoluminescence thermal stability of phosphors is researched. The strategies, emptying and enlarging sites, developed herein are expected to provide a general route for tuning luminescence of phosphors with multiple sites in the future