Search

Abstract: In order to alleviate the effect of the surface defects on the emission properties of quantum dots, copper ions‐doped ZnSe quantum dots (QDs) in the glasses are prepared using melt‐quenching and subsequent thermal annealing methods. For glasses without copper doping, tunable band‐edge emission from ZnSe QDs is achieved. For glasses with copper doping, efficient energy transfer from ZnSe QDs to copper ions is observed, and efficient broad band emission from copper ions is realized at the expense of the band‐edge emission of ZnSe QDs. Absorption spectra, size‐dependent broad‐band emission spectra and electron spin resonance spectra show the cupric ions are doped into the ZnSe QDs. Results reported here shows that doping of transition‐metal ions into semiconductor QDs in glasses is promising for development of high efficient luminescent glasses. [ABSTRACT FROM AUTHOR]

Glass with the composition of 50SiO 2 -25Na 2 O-10ZnO-10BaO-5Al 2 O 3 (in mol%) was used as the matrix for the growth of PbSe QDs. The viscosity-temperature relations of the glass were obtained through Vogel-Tammann-Fulcher equation. PbSe QDs were precipitated in this silicate glasses with the heat-treatment temperatures ( T H ) ranging from 490 to 540 °C for fixed duration of 10 h, corresponding to the glass-viscosity 10 11.2 –10 8.9 Pa·s. Meanwhile, the absorption peaks from PbSe QDs shifted from 872 nm to 2134 nm, and the PL peaks shifted from 1104 nm to 2185 nm. To study the PbSe QDs growth kinetics, the glasses were heat treated at 500, 520 and 540 °C for 1–20 h. Changes in diameter of PbSe QDs exhibited strong time dependencies (i.e. D ~ t 0.17 , T H = 520 °C), while the time dependencies were much smaller than that predicted by the classical Lifshitz-Slyozov-Wagner (LSW) theory (D ~ t 1/3 ) and the higher T H leads to the smaller growth exponent. [ABSTRACT FROM AUTHOR]

CdS/Cd 1−x Zn x S sandwich-structured quantum dots (QDs) were precipitated in silicate glasses with high quantum efficiency up to 53%. The QDs were composed by a CdS core with a Cd 1−x Zn x S shell of about 1–3 nm in thickness through heat-treatment at 550 °C for 10 h. With the increased heat-treatment temperature, the intensity ratio between the intrinsic emission and the defects emission increased and the Stokes shift decreased from 84 to 4 meV, which was caused by both the increased size and passivated surface defects of the QDs. [ABSTRACT FROM AUTHOR]

ZnSe and ZnS nanocrystals (NCs) were precipitated in glasses through heat-treatment. High resolution transmission electron microscope image confirmed that ZnSe NCs were formed in the silicate glasses, and the X-ray diffraction patterns confirmed that ZnS NCs were precipitated in the borosilicate glasses. Absorption shoulders of the ZnSe NCs and ZnS NCs appeared at ~ 2.76 eV and ~ 3.78 eV, corresponding to the bandgap energies of bulk ZnSe and ZnS crystals, respectively. Instead of the intrinsic emissions, broad-band visible photoluminescence from the surface defects or color centers in the glasses was observed from these ZnSe or ZnS NCs. [ABSTRACT FROM AUTHOR]

Modulation of the band gap energy and diameter of quantum dots (QDs) formed in glasses is important to achieve the optimized performance for applications as infrared light sources, lasers, saturable absorbers, etc. Absorption and photoluminescence of PbS QDs were extended into mid-infrared wavelength range in glasses containing small amount of lead but oversaturated with sulfur. Dual-band photoluminescence of PbSe QDs was prepared in oxyfluoride glass-ceramics containing BaF2 nanocrystals. By introducing SnO in the glasses, alloyed Pb1-xSnxSe QDs with smaller band gap energies were formed in glasses, and mid-infrared photoluminescence of Pb1-xSnxSe QDs at ~2570 nm in wavelength was achieved. [ABSTRACT FROM AUTHOR]

Abstract: Optical properties of PbS quantum dots (QDs) precipitated inside the oxide glass matrix were investigated. Photoluminescence (PL) from the PbS QDs showed peak wavelengths located at 1170–1680nm with widths of 150–550nm. Radii of QDs in glasses were 2.3–4.7nm depending upon the thermal treatment. Peak wavelengths of PL bands shifted as much as 70nm as the temperatures and excitation irradiances increased. Calculated effective local temperatures indicated that these shifts of PL spectra were associated with local heating induced by the temperatures and laser beam. [Copyright &y& Elsevier]

Abstract: CdSe quantum dots (QDs) were precipitated in silicate glasses under various durations and temperatures of heat-treatment. Absorption and photoluminescence (PL) spectra of the QDs showed the quantum confinement effect from CdSe QDs. When the glass was heat-treated for 10h, estimated average QD sizes increased from 5.2nm when the glass was heat-treated at 490°C and to 6.9nm when it was treated at 500°C. When the glass was heat-treated at 480°C, estimated average QD sizes were 4.9nm after 20h and 5.3nm after 30h. The PL peak position was independent of the excitation wavelengths; this result indicates that the size distribution of CdSe QDs was narrow. [ABSTRACT FROM AUTHOR]

The formation mechanism of Cd–S–Se quantum dots (QDs) with a CdS/CdSe core–shell structure within a silicate glass system was investigated by monitoring the change in the first excitonic absorption peak of CdSe, CdS, and Cd–S–Se QDs as a function of the heat‐treatment (HT) duration. When a silicate glass containing QD formation components for CdSe or CdS single‐phased QDs was heat‐treated, CdSe QDs grew via Ostwald ripening, whereas CdS QDs hardly formed within the given silicate glass matrix. When the glass, including CdO, ZnSe, and ZnS, was utilized for the synthesis of Cd–S–Se QDs within the glass matrix, Cd–S–Se QDs were successfully formed and exhibited similar growth behavior to CdSe QDs during the initial stage of HT. The structural changes in the QD‐embedded glasses during HT were also monitored by Raman spectroscopy and discussed, and a possible formation mechanism of CdSe/CdS core–shell‐structured QDs within silicate glasses is suggested. [ABSTRACT FROM AUTHOR]

Well‐defined density functional theory (DFT) calculations are performed as the first exploratory study for the atomic and electronic mechanism of defect mediated morphology and optical properties of CdnSen (n = 3, 10, 13, and 33) quantum dots (QDs) in inorganic amorphous matrix. The intrinsic defects of pristine CdSe QDs, and the interfacial defects between the QDs and surrounding amorphous matrix, were systematically studied. The calculated electronic structure suggested that the pristine CdSe QDs capped by the structural modifiers or non‐bridging oxygen in the amorphous matrix gave rise to the structure reconstruction and paired defect states at the edge of the valence and conduction bands. The orbital analysis elucidated that the redistribution of the majority of HOMO and LUMO electron density was localized over the bonds formed by capping atoms and QDs. These changes in the electronic structures were further demonstrated by CdSe QDs embedded sodium silicate glasses. It turned out that Se atoms at QDs/glass interface were much more active than those found on the surface of organically passivated CdSe QDs. The results serve as a new paradigm in materials research to explore structural origins of defect emission from QDs and a new strategy to develop glasses containing QDs with high photoluminescence quantum efficiency. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) properties of PbSe and Sr2+‐doped PbSe quantum dots (QDs) doped in silicate glasses were investigated by changing the excited laser wavelength and intensity. When BaO was replaced by SrO, the Sr2+‐doped PbSe QDs formed and showed large blue‐shifts in both absorption and PL bands compared to the PbSe QDs. It is attributed to the increasing in band gap resulted by the incorporation of Sr2+ ions into PbSe QDs. These two kinds of QDs were excited by the laser with the wavelengths of 1319 and 1532 nm. When rising the pumping intensity up to 1000 mW, the PL intensity from Sr2+‐doped PbSe QDs monotonically increased, while, the PL intensity from PbSe QDs reached maximum at pumping intensity at ~200 mW (λex = 1319 nm) and ~300 mW (λex = 1532 nm). The good resistance to photodarkening of Sr2+‐doped PbSe QDs is indicated passivation effect on the surface defects from Sr2+ ions doping. For Sr2+‐doped PbSe QDs the anti‐Stokes photoluminescence (ASPL) were observed when using both 1319 and 1532 nm excitation. The integrated intensity of the ASPL is linear with the excitation intensity, which indicates that the ASPL belongs to the phonon‐assisted one‐photon process. And the ASPL intensity as a function of excitation intensity shows a size dependence of the QDs. [ABSTRACT FROM AUTHOR]

• Adjusting optical performance of PbS QDs embedded glass to cover the whole telecommunication bands. • Revealing the absorption cross sections of PbS QDs at 1040 nm are 4–13 × 10−16 cm2, the bi- and tri-excitons lifetime is ∼60 and ∼10 ps. • Obtaining the broadband net gain in 1500–1620 nm in single PbS QDs embedded glass with a threshold of < N >=4.1. • Achieving a maximum gain time of ∼20 ps and gain coefficient of >120 cm−1 for PbS QDs embedded glass. Lead sulfide quantum dots (PbS QDs) have a unique performance in the near-infrared (NIR) range. In-situ precipitation of PbS QDs in glass not only improves the stability, but also is easy to be fabricated fiber compatible with silicon photonics. In this work, we reveal that absorption cross sections of PbS QDs at 1040 nm are 4–13 × 10−16 cm2, the bi- and tri-excitons lifetime are∼60 and ∼10 ps due to the trap-assisted Auger recombination using transient absorption (TA). Furthermore, we demonstrate the broadband net gain in 1500–1600 nm in single PbS QDs embedded glass with a gain threshold of < N >= 4.1 (averaged number of excitons), and achieve the maximum gain time of ∼20 ps and gain coefficient of >120 cm−1. These results illustrate the existing obstacles to achieve the net gain in PbS QDs embedded glass, which is important for applications on fiber amplifiers, NIR laser and high-capacity telecommunication. [ABSTRACT FROM AUTHOR]

CsPbBr3−xIx quantum dots were precipitated in boro‐germanate glasses with various Br/I ratios by the melt‐quenching method. When the heat treatment temperature (TH) increased from 480 to 550°C, more I− entered the perovskite crystal lattice, resulting in lattice expansion, the X‐ray diffraction peaks of CsPbBr1.5I1.5 glasses shifted to small angles. The high concentration of I− entered into the perovskite crystal lattice, decreasing the bandgap. The photoluminescence (PL) peaks of CsPbBr1.5I1.5 glasses redshifted from 577 to 620 nm, the PL peaks of CsPbBrI2 glasses shifted from 614 to 636 nm, and the PL peaks of CsPbBr0.5I2.5 glasses shifted from 650 to 672 nm. As the ratio of Br/I reduced from 2.5/0.5 to 0.5/2.5, the PL lifetime of CsPbBr3−xIx glass increased from 2.08 to 74.5 ns. With the delay time from 1 to 1500 ps, the carriers gradually accumulated in the band‐edge state, and the bleaching signal intensity increased. Then more and more carriers returned to the ground state through radiative or nonradiative recombination, the bleaching signal intensity decreased. [ABSTRACT FROM AUTHOR]

Embedding CdTe QDs into glass can improve the thermal and chemical stability of QDs, which facilitates their wide and endurable applications. However, the small tunable spectral range of photoluminescence, low quantum efficiency, and large full width at half maximum limit their wide applications. In this work, effect of introduction of CaO into glass matrix on the formation and optical properties of CdTe QDs is investigated. High concentration of CaO in glasses increases the solubility of Te in glasses, and consequently hinders the precipitation of CdTe QDs in glasses. By adjusting the heat-treatment temperature, average diameters of CdTe QDs are tuned in the range of 2.5–9.0 nm and their photoluminescence bands are tuned from 550 to 800 nm. More importantly, the absolute photoluminescence quantum yield is boosted up to 41.9 %. Results reported in this work indicate that CdTe quantum dots embedded in glasses are promising for applications in light-emitting devices. • High CaO concentration promote the dissolution of Te in the glass. • Photoluminescence of CdTe QDs doped glass is tuned from 550 nm to 800 nm. • PLQY of CdTe QDs doped glasses reaches 41.9 %. [ABSTRACT FROM AUTHOR]

Abstract: The size and spatial distribution of PbS QDs in glasses need to be controlled in order to achieve desired optical characteristics. This paper reports on the use of several rare-earth oxides such as Ho2O3, Er2O3, and La2O3 to control the size of PbS QDs in silicate glasses. Additions of rare-earth oxides result in blue shifts of the absorption bands from 1344nm to 930nm, and the wavelengths of PL bands can be controlled between 1421nm and 1035nm. Additions of up to 0.8mol% of Ho2O3 decreased the diameters of PbS QDs from 4.82nm to 3.02nm. The same tendencies were found for both Er2O3 and La2O3 additions, although the size of PbS QDs increased as the ionic radius of rare-earth ions increased. It is proposed that clusters of RE–O bonds act as nucleating agents for the precipitation of PbS QDs. [Copyright &y& Elsevier]

Lead selenide quantum dots (QDs) were precipitated in lithium-aluminum-silicate glass-ceramics. Their optical properties and the crystallization behavior of both glass host and PbSe QDs were investigated. When the glasses heat-treated at 480–520 °C for 10 h, the absorption bands from PbSe QDs were tuned from 1051 to 2016 nm, and the PL bands from 1165 to 2095 nm. Upon the dwelling time 10 h, the crystallization of glass host required relatively higher heating temperature (∼490 °C) than the formation of PbSe QDs (∼480 °C). With the heat treatment at 490 °C for10 h, the PLQY from PbSe QDs in glass-ceramics reached ∼38.7 %. Phase separation induced the glass crystallization and had a significant effect on the distribution of PbSe QDs. To study the growth kinetics of PbSe QDs, the glasses were heat treated at 480 °C and 500 °C for various durations. The average diameters of PbSe QDs (D) showed exponential relationship to the growth time (t), described by the equation D(t)∼ t x. In rapid growth stage, the growth exponents x is ∼ 0.56 at 480 °C and ∼ 0.47 at 500 °C, and then decrease to ∼ 0.13 and ∼ 0.10, respectively. The formation of a large number of LiAlO 2 crystals in glass hindered the diffusion of semiconductor ions, which is the main reason for the decreasing in the growth rate of PbSe QDs. [ABSTRACT FROM AUTHOR]

Lead chalcogenide quantum dots have particular optoelectronic properties induced by the quantum confinement effects and have promising potentials towards applications in infrared spectral range. Modulation of the optoelectronic properties of lead chalcogenide quantum dots is mainly based on the thermal treatment. In this work, precipitation and optical properties of alloyed PbSe x S 1-x quantum dots in glasses are investigated. Composition, size, absorption, and photoluminescence properties of PbSe x S 1-x quantum dots are modulated by chalcogen elements in glasses and thermal treatment. By adjusting the concentration of ZnSe and ZnS in the glasses, average diameters of the PbSe x S 1-x quantum dots are tuned in the range of 8.1–16.1 nm, their absorption peak wavelengths are tuned in the range of 724–2497 nm, and photoluminescence bands are tuned in the range of 1016–2165 nm with full width at half maximum in the range of 167–517 nm. Fraction of Se in the PbSe x S 1-x quantum dots precipitated in glasses is dependent on the concentrations of ZnSe and ZnS in the glass and heat-treatment temperature. Increase in concentration of S in the glasses results in the reduction of relative fraction of Se in the PbSe x S 1-x quantum dots formed in glasses. More importantly, high heat-treatment temperature promotes the enrichment of Se in PbSe x S 1-x quantum dots, and Se fraction in PbSe x S 1-x quantum dots increases from 0.69 to 0.89, from 0.53 to 0.85, from 0.47 to 0.79, and from 0.45 to 0.76 for those precipitated in glasses with ZnSe/(ZnSe+ZnS) molar ratios of 0.545, 0.375, 0.286, and 0.231, respectively. Increase in ZnSe/(ZnSe+ZnS) molar ratios in glasses also leads to reduction in diameter of PbSe x S 1-x quantum dots formed in glasses. These alloyed PbSe x S 1-x quantum dots also exhibit improved photoluminescence quantum yields and enhanced resistance to thermal quenching of photoluminescence. [Display omitted] [ABSTRACT FROM AUTHOR]

PbS quantum dots (QDs) embedded glasses have been investigated for decades, but their applications are limited to the color filters and saturable absorbers for laser pulse generation so far, mainly due to the low photoluminescence quantum yield (PL QY) induced by the surface defects. Here, by increasing the sulfur to lead molar ratio in the glasses, surface defects of PbS QDs can be partially passivated and the fast trapping of charge carriers is reduced. As a result, PL QY of PbS QDs embedded glasses increases with larger sulfur to lead molar ratio, and PL QY as high as 46.9% is achieved. The improved PL QY along with good thermal and photo-stability makes the PbS QDs embedded glasses promising for near-infrared light generation. By integrating the PbS QDs embedded glass slab with light emitting diode (LED) chip, NIR LEDs with external quantum efficiency of 4.47% (@ ∼1.4 μm) with full width at half maximum larger than 140 nm are realized. Using this approach, it is also versatile to fabricate high-performance and broadband NIR LEDs with PbS QDs embedded glasses as light converters. [Display omitted] • Large molar ratio between S and Pb is beneficial to passivate the surface defects of PbS QDs in glasses. • Photoluminescence quantum efficiency as high as 46.9% was realized for PbS QDs embedded glasses. • Passivation of surface defects of PbS QDs in glasses improved their resistance to temperature and light irradiation. • EQE of near-infrared LED based on PbS QDs in glass as high as 4.47% was achieved. [ABSTRACT FROM AUTHOR]

• Highly luminescent CsPbBr3 PQDs are successfully embedded in a stable tellurite glass host. The influence of structural changes on PL properties is studied. • The enhancement mechanisms related to the Ag doping and structural changes are revealed. • The PLQYs of CsPbBr3 are significantly enhanced to 33.9% in tellurite glasses. Highly luminescent CsPbBr 3 perovskite quantum dots (PQDs)-doped tellurite glasses are prepared by the cost-effective and reproducible melt-quenching and thermal heating method. The photoluminescence quantum yields (PLQYs) are significantly enhanced to 33.9% by glass structural modification and Ag doping. The enhancement mechanisms especially that related to the Ag doping are comprehensively discussed according to high-resolution transmission electron microscope analysis and the first-principles calculation for the first-time. The glass structure dependences of PL emissions are studied as a function of temperature from 78 K to 318 K. Based on the optimized glass sample, robust temperature-, irradiation- and high-current-resistant (up to the highest level of 300 mA yet reported) white light-emitting diode module is realized with an external quantum yield of 20%, a luminous efficiency of 65 lm/W, a correlated color temperature of 4063 K and a good color stability. [ABSTRACT FROM AUTHOR]