On Choosing Phosphors for Near-UV and Blue LEDs for White Light

Abstract

As the lighting industry transitions from traditional technologies to solid state lighting (SSL), it appears that the most preferred way to generate white light using SSL technology has been to use phosphor-converted light emitting diodes (pc-LEDs). There has been considerable debate in the literature whether near-UV LEDs or blue LEDs should be used to excite phosphors for white light. Quite often, in the phosphor literature, the efficiencies of LEDs from 365 nm to 470 nm are somewhat neglected in this debate. In this paper, we have provided data on external quantum efficiency of InxGa1-xN LEDs over the above spectral range, and use these data together with phosphor performance to compare near-UV and blue based approaches to making white light pc-LEDs. We also use simulations to discuss white light blends at two different correlated color temperatures (3000 K and 4000 K) for both LED configurations.

Tunable Eu2+ emission in KxNa1−xLuS2 phosphors for white LED application

“…Therefore, the XRF ratio for K/S combined with the presence of a single ALuS 2 phase directly provides the information about potassium (and indirectly also about sodium) content in this sulfide. The maximum observed value of K/S ratio in this type of sulfide was 4.70 (12) for the pure KLuS 2 sample prepared using 100% K 2 CO 3 . However, due to the strong preference of Na for this ternary sulfide, small concentrations of Na cannot be excluded even in pure KLuS 2 (prepared from 99.997% K 2 CO 3 ).…”

“…Numerous compounds, mostly oxides, phosphates, nitrides, fluorides, were considered as suitable phosphors for constructing W-LED sources, see for example [11][12][13][14][15][16][17][18][19][20][21]. Furthermore, there is the intensive research aiming to find efficient red phosphors to construct white LED based on near-ultraviolet (UV) LED chips coated with RGB tri-color phosphors.…”

New Y2BaAl4SiO12:Ce3+ yellow microcrystal-glass powder phosphor with high thermal emission stability

“…The excitation spectrum shows the maximum intensity at 455 nm, which matches well with the emission of the current efficient blue LEDs (420-460 nm). 3 The fwhm of the emission band is Although new packaging configurations such as the phosphorin-glass, the remote-phosphor-arrangement and the singlecrystal-phosphor were proposed as promising routes to reduce the thermal effect of the LED p-n junction on the phosphor emission, direct coating of the phosphor-polymer mixture onto the LED chip is still the mainstream in the current market. Thus, it is of practical interest to evaluate the thermal emission stability of a new phosphor.…”

“…1 The main way to produce white light from a monochromatic light emitting diode (LED) combines a blue indium gallium nitride (InGaN) with a down-converting phosphor such as (Y,Gd) 3 (Al,Ga) 5 13 are free from patent restriction and may be considered. Compared to the (oxy)nitride candidates, the oxide candidates have a lower synthesis cost and are easier to use in the form of ceramic plate (for application in emerging packaging techniques such as the remote phosphor arrangement 14 which can reduce the thermal effect of the LED p-n junction).…”

Thermodynamics of Light Extraction from Luminescent Materials

“…However, present-day high-current blue top emitting LEDs (no encapsulation or lenses) have published wall-plug efficiencies in excess of 50% at currents above 1 A, 2 clearly demonstrating that light extraction is well above this amount and far above the 10% value for perfectly smooth surfaces. At low current densities, these devices likely have wall-plug efficiencies on the order of 10-15% greater, 3 and correspondingly even greater external quantum efficiencies. Such devices are illustrated in Figure 1b which use surface scattering as one method to recycle and redistribute light to greatly enhance the escape of light that would otherwise remain trapped.…”