Temperature-dependent Optical Propetries Of Colloidal PbSe Quantum Dots And Its Applications

Colloidal quantum dots (QDs) have become research hotspot materials in recentyears. Compared to conventional light emitting material, it has more excellent opticalcharacteristics, such as tunable absorption emission spectra, high quantum yield,preferably light stability, etc. Optical devices fabricated with QDs have theincomparable advantage than other materials. This intrinsic theory and applicationvalue make it has a broad application prospects.In this paper, we used colloidal chemical synthesis method to synthesize varioussizes of PbSe Colloidal quantum dots. The fluorescence quantum yield was measuredto be more than80%. We measured the absorption(Abs) and photoluminescence(PL)spectra of different size PbSe QDs because the optical properties are dependent on its exciton energy structure. It confirmed that the gap width is size-dependent.According to the composition of PbSe quantum dots exciton energy, weestablished theoretically size-dependent calculation model. The QDs shell and thesolvent outside limit the movement of the electron-hole carrier. Using the finitespherical depth potential well model, we analyze the composition of the bandwidthand calculate the contribution of quantum limited and Coulomb effects. Thetheoretical value and laboratories value are accordant.In experiments, we measured the PL spectrum of the different sized PbSequantum dots at different temperature (30-120℃), which proved that the band ofPbSe quantum dots is the temperature size-dependent. When temperature increased,the corresponding PL spectra of the small-sized PbSe quantum dots (3.6nm) shifted tored, with its band gap narrowing. For large-sized (6.0nm) PbSe quantum dots, the PLspectra shifted to blue with temperature increasing. There is a critical size(5.1nm), theband gap of PbSe quantum dots does not change with temperature. We analyzedvarious factors which impact on the band gap, including: thermal expansion, the roleof exciton-phonon coupling effect, which prompted positive contribution to band gap,and quantum limited energy, Coulomb role energy, polarization energy, whichprompted negative contribution to band gap. These factors lead to the emergence of the turning point.We used the lattice relaxation theory to explain the relationship betweentemperature and the PL spectral intensity, full width at the half-maximum(FWHM) ofPbSe quantum dot, and obtained the corresponding formula. Then applyingexperimental data to fit curves and obtained formula parameters. Also we studied thereversibility and repeatability of PL spectrum varies with temperature, and it provedthat the PbSe quantum dots have a higher stability.PbSe quantum dots (QDs) were employed as a real-time and on-chip temperaturesensor to monitor the surface temperature of GaN LED chips. The surface temperatureof the light-emitting area were measured from front side of each LED chip by usingan infrared (IR) thermal image camera.The temperature-dependentphotoluminescence spectra were achieved. The nanosized QD sensor did not influencethe LED emission spectrum due to its infrared emission and little absorption. Thesurface temperature of GaN LED chips was analyzed at different working time andvoltages. The temperature sensitivity characterized by the photoluminescence peakposition of PbSe QDs was found to be0.15nm/℃in a range of30-120℃and theprecision were determined to be±3℃. The QD surface temperature sensor wasconfirmed to have good reversibility and repeatability.