White LEDs with limit luminous efficacy

Abstract

Degradation and corresponding failure mechanism for GaN-based LEDs AIP Advances 6, 055219 (2016) Abstract. In most promising widespread gallium nitride based LEDs emission is generated in the blue spectral region with a maximum at about 450 nm which is converted to visible light with the desired spectrum by means of phosphor. The thermal energy in the conversion is determined by the difference in the energies of excitation and emission quanta and the phosphor quantum yield. Heat losses manifest themselves as decrease in the luminous efficacy. LED heating significantly reduces its efficiency and life. In addition, while heating, the emission generation output and the efficiency of the emission conversion decrease. Therefore, the reduction of the energy losses caused by heating is crucial for LED development. In this paper, heat losses in phosphor-converted LEDs (hereinafter chips) during spectrum conversion are estimated. The limit values of the luminous efficacy for white LEDs are evaluated.

Complex study on photoluminescence properties of YAG:Ce,Gd phosphors

“…It can be found that the diffraction peak of (420) moves to the lower angle side with the increase of Gd 3+ content relative to the position in the crystal. It is assumed [7] that the shift of the peak (420) is caused by lattice distortion and substitution of ions Y 3 + (0.92Å) by ions Gd 3 + (0.938Å). Figure 2(а) shows excitation spectra of tested phosphors at the fixed emission wavelength of 560 nm, two bands can be seen in the region between 300 and 500 nm and these are peaked at 344 and 454 nm.…”

Tunable lanthanide/transition metal ion‐doped novel phosphors for possible application in w‐LEDs: a review

“…In gallium nitride (GaN)‐based LEDs, emission occurs at around 450 nm and is then converted into white light by the suitable phosphor of the choice. There is an intricate play between excitation and emission energies, the quantum yields of the phosphor that are required for the thermal energy of the above‐mentioned conversion . Some of the charge carriers recombine with emission, while others undergo nonradioactive decay during recombination on the lattice defects (primarily dislocations).…”

Luminescence Spectrum of Yttrium Aluminum Garnet Based Phosphors with Initiating by Different Sources of Optical Excitation

“…The phosphors provide high transformation output radiation of the chip at 452 nm in visible light, the possibility of obtaining the desired luminescence spectrum in the visible region of the spectrum. Nowadays, many different phosphors are developed, which provide a luminous efficacy of LEDs 160 Lm/W and a radiation with different color coordinates [2][3][4][5]. However, the processes of excitation and luminescence, nature of luminescence centers are studied insufficiently.…”