Luminescence Studies of Transition Metal (Cu+ and Ag+ Ions) Activated Alkali Zinc Mixed Phosphate

Because of the importance of inorganic phosphates in the solid-state lighting industry, KZnPO4 doped with some transition metal dopant ions like Cu+ and Ag+ ions were prepared by low-cost co-precipitation method at room temperature followed by annealing at a high temperature around 6500C. The prepared phosphors were characterized by X-ray diffraction. In the case of a Photoluminescence study for KZnPO4 doped with Cu+, the emission was observed at 425 nm, which corresponds to the emission of Cu+ ion. In the case of Ag+ doped KZnPO4, weak emission was observed at 420 nm, which is assigned to the emission of Ag+ ions. CIE chromaticity coordinate of KZnPO4 doped with Cu+ and Ag+ ions phosphor was also evaluated via using OSRAM SYLVANIA color calculator and colour purity of concentration was nearly 95% of Cu+ and Ag+ ions. The obtained outcomes revealed that the prepared phosphor shows potential application in the field of solid-state lighting.

Simple-Structured OLEDs Incorporating Undoped Phosphorescent Emitters Within Non-Exciplex Forming Interfaces: Towards Ultraslow Efficiency Roll-Off and Low Driving Voltage for Indoor R/G/B Illumination

To meet the requirement of indoor R/G/B monochrome illumination a simplified OLEDs structure and fabrication process must occur. Herein, a design philosophy of low efficiency roll-off and simple-structure OLEDs incorporating R/G/B phosphorescent ultrathin non-doped emissive layers (EMLs) within non-exciplex forming interfaces a luminescent system by a direct charge trapping mechanism has been reported, which uses bis(2-methyldibenzo[f,h]-quinoxaline)(acetylacetonate)iridium(III) (MDQ)2Ir(acac), bis(3-phenylpyridin-e)iridium(III) (Ir(ppy)3), and bis(3,5-difluoro-2 -(2-pyridyl)phenyl-(2-carboxypyridyl) iridiumII) (Firpic) as R/G/B luminescent dyes, respectively. Although the recombination zone is narrow in the designed OLEDs, the efficiency roll-off of the designed OLEDs are unexpectedly slow, due to stable charge trapping of the emitters and are refrained from concentration quenching in relatively low current density, but the luminance meets the requirement of indoor lighting. With a low threshold voltage of 2.9/2.9/3.5 V, the designed R/G/B phosphorescent OLEDs show an efficiency roll-off as low as 7.6/3.2/4.3% for indoor luminance from 10 cd/m2 to 1,000 cd/m2, respectively. The perspective of R/G/B luminescent dyes on luminous efficiency, chromaticity coordinate drifts, efficiency roll-off, and direct charge trapping has been thoroughly studied. Therefore, our research may help to further develop ideal indoor lighting using a simplified undoped R/G/B OLEDs structure with simultaneous ultraslow efficiency roll-off, low threshold voltage, simplified fabrication process, low reagent consumption, and cost.

Light Output, Thermal Properties, and Reliability of Using Glass Phosphors in WLED Packages

White-light-emitting diodes (WLED) based on yttrium aluminum garnet (YAG) phosphors sintered with glass (PiG) and with silicone (PiS) are compared in terms of their light properties, temperature properties and reliability.The complete YAG phosphor was doped with an encapsulant traditional WLED (PiS WLED), and the WLED was covered with PiG (PiG WLED). PiG was made by sintering glass powder and YAG phosphor at the ratio of 87:13 (%), and the correlated color temperature (CCT) was 5564 K. The CCT of the PiG WLED with the YAG doping concentration of 8.5 wt.% approximated 5649 K. The initial light output of the PiG WLED was 6.4% lower than that of the PiS WLED. Under 1008 h and 350 mA aging, PiG WLED and PiS WLED’ light output, CCT and color rendering index variation rates were all within 1%. In the saturated vapor-pressure test, no sample exhibited red ink infiltration, light nor peeling between the encapsulant and the lead-frame. Compared with that of the PiS WLED, the junction temperature of the PiG WLED reduced from 88.4 °C to 81.3 °C. Thermal resistance dropped from 37.4 °C/W to 35.6 °C/W. The PiG WLED presented a better CIE (Commission Internationale de l’Eclairage) 1931 chromaticity coordinate (x,y) concentration and thermal properties than the PiS WLED.

Novel red-emitting Lu3Te2Li3O12: Eu3+ phosphor with high color purity for n-UV WLEDs

In this work, a series of red emitting Lu3Te2Li3O12: Eu3+ phosphors were synthesized for the first time by high temperature solid state reaction. The structure was characterized by X-ray diffraction. The excitation spectra, emission spectra and CIE chromaticity coordinate were studied. The phosphors show strong red emission at 611 nm due to the 5D0-7F2 transition of Eu3+ ions. The optimal doping concentration of Eu3+ in LTL host is x = 0.5 due to the concentration quenching mechanism of dipole-dipole interaction. The CIE chromaticity coordinates of the LTL: 0.5Eu3++ phosphor is (0.644,0.355), and the purity of the color is up to 93.61%. The phosphor can be considered as a potential red-emitting candidate for near UV WLEDs.

Circadian stimulus – A computation model with photometric and colorimetric quantities

The circadian stimulus is an important, validated and updated metric that describes the invisible influences of light on the human circadian system explicitly and scientifically. However, an absolute spectral power distribution must be supplied for its computation, which is only measurable by an expensive and complicated spectrometer. This paper proposes an alternative circadian stimulus computation model that is identified as the function CS(z, Ev) for white light sources based on the most common and simplest parameters of illuminance Ev in lux and the chromaticity coordinate z. These parameters are well known and widely used in both colour science and lighting technology. In order to prove the accuracy and availability of the model, an internal validation was performed with the adapted method repeating split data to check the goodness of the model fit. The fitted model achieved a maximum residual of 0.058 in the circadian stimulus quantity (R2 = 0.998). An external validation with the maximum residual of 0.030 (R2 = 0.999) provided stronger evidence for the usability of the model in applications.

Photoluminescence properties of Li2+xNb3xTi1−4xO3:Eu3+

Red phosphors with compositions of Li[Formula: see text]Nb[Formula: see text]Ti[Formula: see text]O3:3[Formula: see text]wt.% Eu[Formula: see text] [Formula: see text] were synthesized by solid-state reaction method. The samples were investigated by using X-ray diffraction (XRD) and photoluminescence spectroscopy, respectively. XRD results showed that all samples were main phase of Li2TiO3. Emission spectra of Li[Formula: see text]Nb[Formula: see text]Ti[Formula: see text]O3:3[Formula: see text]wt.% Eu[Formula: see text] powders showed strong red emission at 612[Formula: see text]nm (5D0–7F[Formula: see text] with 396[Formula: see text]nm excitation. In addition, the excitation and emission intensity increased up to [Formula: see text], and then decreased with further increasing of the x values. And the chromaticity coordinate (CIE) of the component with [Formula: see text] was superior to other components.

Preparation and luminescence properties of Li2.06Nb0.18Ti0.76O3:Eu3+ phosphors

New red phosphors with compositions of Li[Formula: see text]Nb[Formula: see text]Ti[Formula: see text]O3: [Formula: see text]Eu[Formula: see text] ([Formula: see text]–4[Formula: see text]wt.%) were prepared by using solid-state reactions. The phase structure and photoluminescence (PL) properties were studied as functions of synthetic temperature and Eu[Formula: see text] concentration. With the increase of synthetic temperature and Eu[Formula: see text] concentration, both the characteristic peaks of the excitation spectra monitored at 612[Formula: see text]nm and emission spectra excited at 396[Formula: see text]nm were remarkably enhanced. The intensity of peaks reaches a maximum when the content of Eu[Formula: see text] increases to [Formula: see text][Formula: see text]wt.% at 950∘C, Chromaticity Coordinate (CIE) of samples superior to the commercial red phosphors Y2O3:Eu[Formula: see text]. The internal quantum efficiency (QE) of Li[Formula: see text]Nb[Formula: see text]Ti[Formula: see text]O3:3[Formula: see text]wt.%Eu[Formula: see text] was 49.5%. These features show promising applications for near-ultraviolet (near-UV) chips-based LEDs.

Optimization of LaPO4:Bi3+ Single-Phased White-Emitting Phosphor Luminescence Properties by Li+/Na+ Doping

LaPO4:Bi3+ single-phased white-emitting phosphors doped with both Li+/Na+ ions were successfully prepared by a conventional solid-state reaction technique. Microstructures were analyzed by both X-ray diffraction and high-resolution scanning electron microscopy experiments. Under the excitation of 335 nm, the La0.97PO4:Bi3+0.03 phosphor showed four emission bands with maxima at 460 nm, 487 nm (blue), 530 nm (yellow), and 637 nm (red); these can be successfully combined to form pure white light in a single host lattice only by simple activator Bi3+ ion. It was found that changing the concentration of dopant (Li+, Na+ ions) did not produce a change in shape or location of the emission peaks, but the value of the emission intensity increased; this was particularly evident in the red emission, which could optimize the white light emitting performance of the phosphors. When the Na+ doping concentration was 0.02, the CIE chromaticity coordinate of phosphor La0.95PO4:Bi3+0.03, Na+0.02 was (0.3008, 0.3203), close to that of the standard white light.

Single-Composition White Light Emission from Dy3+ Doped Sr2CaWO6

A series of Dy3+ ion doped Sr2CaWO6 phosphors with double perovskite structure were synthesized by traditional high temperature solid-state method. It was found that there is significant energy transfer between Dy3+ and the host lattice, and the intensities of emission peaks at 449 nm (blue), 499 nm (cyan), 599 nm (orange), 670 nm (red), and 766 nm (infra-red) can be changed by adjusting the concentration of dopant amount of Dy3+ ion in Sr2CaWO6. The correlated color temperature of Dy3+ ion doped Sr2CaWO6 phosphors can be tuned by adjusting the concentration of Dy3+ ion. Upon optimal doping at 1.00 mol% Dy3+, white light with chromaticity coordinate (0.34, 0.33) was emitted under excitation at 310 nm. Thus, single composition white emission is realized in Dy3+ doped Sr2CaWO6.