Optical And Thermal Performances Investigation Towards Quantum Dots-White Light-Emitting Diodes

Recently,quantum dots(QDs),as a new kind of luminescent nanocrystal,have gained wide applications in lighting and display areas due to their high optical efficiency,preciselyadjustable wavelength and narrow full-width-at-half-maximum(FWHM).The quantum dots-white-light-emitting diodes(QDs-WLEDs)are also called ‘the next generation lighting and display source’.To realize white light illumination,LED chip,phosphor,QDs and polymer gel need to be packaged into the same LED leadframe.While,in the packaging process,the chemical structure of QDs is easily damaged by other packaging materials,leading to luminescence droop or quenching.Therefore,it is not easy to achieve a white spectrum with high optical efficiency and color quality.Besides,due to the heat generation in LED chip and phosphor/QDs materials,the working temperature of white LEDs may become extremely high,and the QDs will face failure due to their poor thermal stability.However,there are less packaging or thermal management strategies referring to the QDs’ temperature control.Researches regarding to those optical and thermal issues have been conducted as follows:An optical-thermal conversion model of QDs was established.To precisely describe the opto-heat conversion process in QDs film,a double integrating spheres(DIS)system was built.The DIS system was then combined with the inverse adding doubling(IAD)algorithm to measure the absorption,scattering and anisotropy coefficients of QDs.The experiments show that the maximum deviation of this model is less than 1.16%,suggesting that this model can be used to calculate the heat generation of QDs during the conversion process.A QDs-luminescent mesoporous silica(QLMS)composites was proposed to solve the chemical compatibility and oxygen/moisture penetration problems.Via a swelling and evaporation method,the QDs were embedded into the nano-porous channels of mesoporous silica,so that the QDs can be protected from oxygen and moisture damage.Reliability tests suggest that the optical stability of QDs was enhanced by 122% after this treatment.Considering the human circadian rhythm,we optimized the spectrum of QDs-WLEDs.Based on the circadian action factor(CAF)optimization,we obtained the optimal spectra of QDs-WLEDs with wide CAF variability.With a high color rendering index(CRI)above 90,the maximum CAF variability can be tuned by 3.83 times.Based on the optimal spectra,we also fabricated the QDs-WLEDs with CRI > 95,and realized a maximum CAF variability of 3.15 times.A new packaging structure was proposed to reduce the working temperature of QDs in QDs-WLEDs.In order to produce more light energy and reduce heat generation,we analyzed the packaging structure of QDs-WLEDs,and proposed a QSNs-on-chip structure.Experimental results show that this new structure improves the luminous efficiency by 15.7% and reduce the QDs’ working temperature by 33.6 ℃.To solve the problem that the thermal conductivity of QDs gel is too low,a QDshexagonal boron nitride(QDs-hBN)luminescent composites with high thermal conductivity was proposed.By the electrostatic effect,the QDs nanocrystals were attached onto the hBN platelets surface.The experiments show that under an hBN filling volume fraction of only 2%,the thermal conductivity of QDs gel was enhanced by 58%.Subsequently,the QDs’ working temperature was reduced by 22.7 ℃.