Analysis of the factors governing the enhanced photoluminescence brightness of Li-doped Y2O3:Eu thin-film phosphors

Abstract

The authors studied the Li concentration dependence of the internal efficiency and extraction efficiency contributions to the enhanced photoluminescence (PL) brightness of the Li-doped Y2O3:Eu thin films. Experiments conducted with excitation at a wavelength of 254nm showed that adding 20mol% Li2CO3 to conventional Y2O3:Eu thin films improved their PL brightness by a factor of over 7.0. This improvement is attributed to enhanced internal factors (crystallinity, grains, and substitution of interstitial oxygen) and the increased optical volume (thickness), as well as the reduction of photon trapping in the high-index guiding layers of the Y2O3:Eu thin films. They also discuss how to quantitatively determine the contributions of the internal efficiency, the extraction efficiency, and the optical volume to the enhanced PL brightness of the Li-doped Y2O3:Eu thin-film phosphors.

Review paper: Semiconductor nanoparticles with surface passivation and surface plasmon

“…Lowdimensional structures exhibit fascinating behavior and have a multitude of potential applications, such as Li-ion batteries, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] fuel cells, [19][20][21][22][23][24][25][26] nanophosphors, [27][28][29][30][31][32][33] and solar cells. [34][35][36][37][38][39] Semiconductor nanocrystals have attracted much attention due to their unique optical properties, which originate from the quantum-confinement effect. Specifically, the confinement of charge carriers and bandgap engineering can be achieved by changing the size of the semiconductor nanoparticles.…”

Enhanced photoemission from nanoscale agglomerations in Li co-activated Y2O3:Eu3+ thin films

“…A more reduced symmetry of these sites would then result in the enhanced luminescent properties [33]. Origin of this large enhancement in PL brightness is complex [13,15]. The increase in intensity is due to several effects, such as crystallinity (or increase in the oscillation strength), grain size, nano-agglomerations and the substitution of Li for interstitial oxygen (an increase in the hole concentration).…”

“…Furthermore, luminescent properties of nanostructured phosphors can be enhanced by the introduction of suitable co-dopant materials to phosphor matrix. It is reported [13][14][15] that even in very small quantities, Li + ions, as co-dopant, can play an important role in increasing the luminescent efficiency of bulk phosphors. Techniques like sputtering, pulsed laser deposition, vacuum evaporation, electron beam evaporation, spray pyrolysis and chemical deposition [11,[16][17][18][19][20] have been used for the preparation of yttrium based oxide thin films.…”

Laser spectroscopic investigation of lithium doping effect on luminescence enhancement in YVO4:Eu3+ thin films

“…In 1996 Yeh and Su [2] showed that the mixing of LiF in Gd 2 O 3 :Eu 3+ phosphor increases its thermo-and photo-luminescence sensitivities. After that, the luminescence enhancement by Li substitution has been reported in zinc compounds (ZnO:Dy 3+ ) [3], polycrystalline garnet (Y 3 Al 5 O 12 :Tm 3+ ) [4], microcrystalline compounds (Gd 2 O 3 :Eu 3+ [5] and Y 2Àx Gd x O 3 :Eu 3+ [6]), nanosized Y 2 O 3 :Eu 3+ phosphors [7], and thin film phosphors (Y 2 O 3 :Eu 3+ [1], Gd 2 O 3 :Eu 3+ [8], and YVO 4 :Eu 3+ [9]). It has been suggested that the luminescence enhancement by Li doping is due to the improved crystallinity, enhanced surface morphology, increase in surface roughness, reduction in internal reflection [5,6,8], and decrease in interstitial oxygen and increase in hole concentrations [10] by means of X-ray diffraction (XRD), scanning emission microscope (SEM), atomic force microscope (AFM), and transmission electron micrograph (TEM).…”

“…The luminescence efficiency of thin films, however, is lower than that of powder phosphors due to the poor light extraction efficiency and poor internal efficiency [1]. One of the most important requirements for the phosphors is a sufficient luminescence efficiency which is governed by numerous factors in the materials.…”