Evolution of Luminescence from Doped Gallium Phosphide over 40 Years

Abstract

The results of luminescence studies conducted on the same samples of GaP over a 40-year period are discussed. The results strongly imply that periodic ordering of impurities improved the overall optical and mechanical properties of the material over time. Forty years after preparation, ''hot'' luminescence spectra in gallium phosphide (GaP) are similar to those for nanocrystals. The aged pure and N-doped crystals exhibit stimulated emission at 300 K. The aged GaP:N:Sm at room temperature generates bright green or yellow and red tunable luminescence. These results correlate with Raman light scattering and microhardness data obtained from the same crystals.

Excitonic Crystal and Nanotechnology

“…As first noted in Ref [11], these results suggest a new type of crystal lattice in which the host atoms occupy their proper (equilibrium) positions in the crystal, while the N impurities, periodically substituted into the lattice portion it into short chains of equal length. According to the data obtained from Raman light scattering [9,13] host atoms of this new lattice develop harmonic vibrations, and high degree of lattice perfection leads to an abrupt decrease in the non-radiative recombination and an increase of efficiency and spectral range of luminescence.…”

“…Additionally, stimulated emission of light in these temporally-ordered crystals (Figure 2b) is observed. As also shown in Ref [11] the GaP:N crystals aged for at least 40 years possess no discrete impurity level for N-bound excitons in the forbidden gap. They also demonstrated a uniform luminescence from a broad excitonic band instead of the narrow zero-phonon line and its phonon replica as observed from the less-aged 25 year-old crystals.…”

“…Presently, our ordered crystals have a bright luminescence at room temperature that implies their perfection and very low light losses. In our studies [11,13] we demonstrate that the stimulated emission is also developed even at room temperature by direct electron-hole recombination of an electron at the bottom of the conduction band with a hole at the top of the valence band and the LO phonon absorption.…”

“…These, along with other half-centennial findings, including modifications to luminescence kinetics, spontaneous Raman scattering, x-ray diffraction, absorption spectra, micro-hardness and density of dislocations, that are reported elsewhere [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] strongly suggest that close-to-ideal GaP:N crystals are formed over time through the equally-spaced disposition of N impurities from their chaotic distribution in the same freshly prepared crystals.…”

“…Evaluation of the characteristic time of such reordering, based on the known Ising model, suggests that the time for the substitution reaction associated with N diffusion along P sites in GaP:N is about 15 years at room temperature [1]. Accordingly, observations of the luminescence from GaP:N crystals made at 10-15 year intervals under similar experimental conditions were used successfully to track such structural evolution [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. In this paper, as well as in the works published in 2012-2013 [14][15][16] we report the cumulative effects of over 50 years of lattice ordering on properties of GaP single crystals, providing clear evidence for enhanced optoelectronic properties through temporal dynamics over long time periods.…”