Structure of Photoluminescence Spectra of Oxygen-Doped Graphitic Carbon Nitride

Abstract

The relationships governing variation of the photoluminescence of graphitic carbon nitride synthesized by heat treatment of melamine in a closed air medium containing oxygen in the temperature range of 10-300 K were investigated. It was shown that the concentration of oxygen in the obtained material 4-5 at.% increases with increase of temperature and decreases with increase in the duration of the synthesis process. By measurements at reduced temperatures right down to 10 K it was possible to resolve bands due to radiative recombination processes in the photoluminescence spectra of the graphitic carbon nitride. It was found that increase of the synthesis temperature from 500 to 600 o C and also increase of the duration at the given temperature from 30 to 240 min shift the maximum in the photoluminescence spectrum from 2.74 eV into the region of lower energies to 2.71-2.67 eV. This is due to the bigger role of the molecular system formed by the π bonds of carbon and nitrogen atoms with sp 2 hybridization and characterized by a smaller forbidden band width in the emission of light. Transitions due to recombination through oxygen-induced levels in the forbidden band of the semiconductor lead to the appearance of a "tail" in the photoluminescence spectra in the region of low energies (2.40-2.33 eV). Increase of the carbon nitride synthesis temperature to 600 o C leads to a change in the structure of the energy bands and to increase of the energy of the radiative transitions as a result of increase in the degree of doping with oxygen atoms and thermal stratifi cation.

Chemical Vapor Deposition of 2D Crystallized g-C3N4 Layered Films

“…Luminescence of the synthesized thin films has much in common with that of bulk g -C 3 N 4 synthesized from melamine . The observed red shift of PL is caused by the change in the intensity ratios for the recombination processes involved (Figure b) in g -C 3 N 4 synthesized at different temperatures.…”

“…Luminescence of the synthesized thin films has much in common with that of bulk g-C 3 N 4 synthesized from melamine. 21 The observed red shift of PL is caused by the change in the intensity ratios for the recombination processes involved (Figure 5b) in g-C 3 N 4 synthesized at different temperatures. With an increase in the synthesis temperature, the role of radiative transitions with lower energies increases, which is a result of the changes in the material energy band structure.…”

TiO2-Based Heterostructure Containing g-C3N4 for an Effective Photocatalytic Treatment of a Textile Dye

“…Some researchers a 𝜋 * and σ* leading to absence of σ*-n and a 𝜋*-n tran emission) instead [42][43][44]. Others keep attributing the firs σ*-n transition, and explain its red shift with band gap n higher temperature (550 °C in the present case) [45][46][47][48]. tense peaks at around 450 nm and 480 nm are usually assig Convolution of the obtained PL spectra from these two p However, an even better multipeak Gaussian fitting was o lapping peaks.…”

Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis

“…The most common ways to introduce elemental oxygen into g-C 3 N 4 (Table 1) are oxidation methods, such as oxidation of g-C 3 N 4 with acids [11][12][13], thermal oxidation [14][15][16][17][18][19][20][21][22][23], oxidation with 2.79 eV. The doping of oxygen improved the separation of photo-generated carriers that was concluded from the decreasing PL intensity after oxidation of g-C 3 N 4 with PMS.…”